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Calcium

Other common name(s):

calcium carbonate, calcium gluconate, calcium citrate

Scientific/medical name(s):

Ca, Ca++

Description

Calcium is a mineral that is vital for a number of body functions, such as contracting muscles (including the heart), secreting hormones, and sending messages through the nervous system. Most of the body's calcium is in the bones and teeth, but a small amount circulates in the blood for these important tasks. The human body can't make calcium, so it must be taken in from foods or supplements.

Calcium is found naturally in many dairy products, leafy green vegetables, and fish. In the United States, it is added to many foods, like some brands of orange juice, cereal, and milk substitutes like soy or rice milk. Calcium is the active ingredient in certain antacids.

Overview

Many people, especially women, can benefit from keeping up with their calcium intake to help prevent bone problems such as severe bone thinning (osteoporosis). Calcium supplements will not slow the growth of most cancers, but they appear to reduce the risk of pre-cancerous polyps of the colon. Studies of calcium supplements with vitamin D have shown some promise in cancer risk reduction, but results have been mixed. In fact, high doses of calcium have been linked to a higher risk of prostate cancer. Calcium supplements may be important for some people with cancer, depending on their stage, cancer type, and the type of treatments they get.

How is it promoted for use?

Calcium is best known for its role in growing strong bones and teeth in children and teens, and keeping them strong into adulthood and old age. Calcium is less known for helping the heart and other muscles do their work, but some companies promote this function as well.

Calcium is mainly promoted for bone health. The United Sates Food and Drug Administration (FDA) has approved certain limited health claims about calcium supplements. Now, companies that sell calcium supplements can legally make statements such as these:

Adequate calcium throughout life, as part of a well-balanced diet, may reduce the risk of osteoporosis.

Adequate calcium and vitamin D as part of a healthful diet, along with physical activity, may reduce the risk of osteoporosis in later life.

At one time, certain types of calcium were promoted as cures and preventions for many types of diseases. More makers of calcium now stick to what is better known about calcium, that it can help promote bone density, and protect bone health.

Some makers of calcium promote their formulas as better than others in some way. For example, certain companies say that extra minerals in the calcium make it work better. Others may state that calcium from coral has more helpful health effects or that calcium made from algae is absorbed more easily by the body.

What does it involve?

Calcium intake from healthy foods is the best source, but calcium supplements can be found in drug stores, grocery stores, health food stores, and via the Internet. Supplements are most often made from calcium carbonate, though calcium citrate and other compounds are also sold. Calcium carbonate is also the form found in antacids like Tums® and Rolaids®.

The Institute of Medicine updated its calcium requirements in 2010. The new Recommended Dietary Allowance (RDA) for calcium is 1,000 milligrams per day for men and women aged 19 through 50, and for men between 50 and 70. The RDA is 1,200 milligrams per day for women over 50 and men over 70. Some nutritionists and doctors recommend that calcium supplements be taken with supplements of vitamin D and other important minerals, such as magnesium and potassium. And vitamin D is required to be able to absorb calcium into the body. (See our document, Vitamin D.)

The body's use of calcium is complex. It is affected by many hormones and factors other than how much calcium a person eats or takes in. There are many ways to treat bone problems and calcium imbalance in the body, depending on their cause.

The best source of calcium is a balanced diet, which helps to avoid bone problems and decreases the risk of some types of cancer. Foods and beverages high in calcium include milk and other dairy products (low-fat products are healthier), leafy green vegetables such as broccoli and greens, nuts, seeds, beans, tofu prepared with calcium, cheese, dried figs, kelp, oysters, and canned fish that can be eaten with the bones still in it, such as sardines and salmon. Certain brands of cereals, orange juices, and soy and rice milks are fortified with calcium and are clearly marked as such on the label.

What is the history behind it?

The importance of calcium for maintaining overall health and promoting bone strength has been known for decades. Some scientists believe that humans became accustomed to diets high in calcium as far back as 35,000 years ago. Calcium's role in preventing or slowing the growth of cancer has only become a subject of research within the last 20 years or so.

What is the evidence?

A number of important studies to measure calcium's impact on cancer have been published in peer-reviewed medical journals. Several studies have suggested that foods high in calcium might help reduce the risk for colorectal cancer. These studies also suggest that calcium supplements may somewhat reduce the risk of adenomas, which are a type of polyps in the colon and rectum that can progress to cancer. More recent studies have noted that women with higher dietary calcium intake seemed to have lower risk of breast cancer. This risk was not affected by calcium supplements.

One researcher reviewed several dozen studies of the effects of calcium on various diseases and concluded that long-term deficiencies in calcium and vitamin D may lead not only to fragile bones, but also to colorectal cancer and high blood pressure in some people. Getting enough calcium may help to prevent these conditions in some.

Randomized clinical trials are now starting to study the role calcium may play in cancer prevention. A Women's Health Initiative study published in 2006 put more than 36,000 menopausal women into 2 groups: half got calcium with vitamin D and half got a placebo (sham pill). After 7 years, the researchers looked at colorectal cancer risk in the 2 groups. Cancer risk was not lower in the group that took calcium. Critics of the study noted that many women were not taking their pills at all. The average calcium and vitamin D intake of the women at the start of the study was also about twice as high as the national average, and close to the doses used in the study. And finally, women in the study were allowed to take extra calcium and vitamin D if they wished. This means that many women who were thought to be on placebo may have taken the same or higher doses as those who were in the test group. These factors may have limited the ability of the study to find any differences. Researchers will keep watching the women until late 2010, so there may be more information at that time. A report on this study from 2009 showed no difference in death rates between the test group (women given calcium and vitamin D supplements) and those who were not given them.

A randomized clinical trial reported in 2007 found lower risk for all cancers combined in women given calcium supplements than in women taking the placebo. Cancer risk was even lower among women taking both calcium and vitamin D. Doses in this study were higher than in the Women's Health Initiative study above.

While further research is needed to clarify the role of calcium in preventing or reversing cancer growth, there is little doubt that adequate calcium intake is required for preventing bone shrinkage and weakening. For people who have cancer, calcium and vitamin D intake may help keep bones strong.

Some chemotherapy medications can reduce appetite, create swallowing difficulties, cause nausea and vomiting, and result in osteopenia (thinning bones). The chemotherapy drugs methotrexate and doxorubicin may directly damage bones. Some hormonal therapies used in the treatment of breast or prostate cancer can also weaken bones. Radiation therapy can cause osteopenia within the area being treated, and the combination of radiation therapy and chemotherapy can cause even greater damage to bone structure. Some cancers also can harm bones. Adequate calcium intake is important for bone health in the general public and in cancer survivors, and especially those with osteoporosis, but calcium intake is not the only factor that affects bone health. Physical activity is also important in keeping bones strong. And there are several kinds of medicines available to treat osteoporosis.

Calcium has also been found helpful in reducing certain symptoms of premenstrual syndrome. There is some early evidence that calcium may play a role in helping to prevent heart disease and reducing insulin resistance in diabetic patients.

Because calcium plays a crucial role in bone mass and strength, its greatest benefit to people with cancer may be to lower the risk of thinning bones or reduced bone mass (osteopenia). This can worsen until the bones get fragile and break easily (osteoporosis). Both conditions are linked closely to aging, and osteoporosis is a common problem for women after menopause. Weak bones can also result from poor nutrition, prolonged drug therapy, disease, and poor mobility, all of which may apply to people who have cancer.

Are there any possible problems or complications?

This product is sold as a dietary supplement in the United States. Unlike companies that produce drugs (which must be tested before being sold), the companies that make supplements are not required to prove to the Food and Drug Administration that their supplements are safe or effective, as long as they don't claim the supplements can prevent, treat, or cure any specific disease.

Some such products may not contain the amount of the herb or substance that is on the label, and some may include other substances (contaminants). Actual amounts per dose may vary between brands or even between different batches of the same brand. In 2007, the FDA wrote new rules to improve the quality of manufacturing for dietary supplements and the proper listing of supplement ingredients. But these rules do not address the safety of the ingredients or their effects on health.

Most such supplements have not been tested to find out if they interact with medicines, foods, or other herbs and supplements. Even though some reports of interactions and harmful effects may be published, full studies of interactions and effects are not often available. Because of these limitations, any information on ill effects and interactions below should be considered incomplete.

For most people, the greatest risk with calcium comes from not getting enough of it. In rare cases, taking in large amounts of calcium (usually more than 2,400 milligrams a day) from dairy foods, supplements, and antacids can lead to a condition called milk alkali syndrome. It throws off the balance between acids and bases in the blood, with high levels of calcium (hypercalcemia), dehydration, and kidney problems. Weakness, mental confusion, irritability, vomiting, and kidney damage can result. Over the long term, too much calcium can also cause kidney stones, muscle pain, red eyes, and deposits of calcium in the muscle tissue.

It is also possible to get high calcium levels from taking in too much vitamin D, usually from supplement overuse. But for people with cancer, high calcium levels are most often caused by the cancer itself, especially in its later stages. Hypercalcemia from any cause is treated as a serious medical problem.

Calcium can keep other minerals such as iron, zinc, magnesium, and phosphorus from being absorbed. Calcium can also prevent or reduce the absorption of certain medicines, so talk with your doctor or pharmacist about all medicines and supplements that you are taking.

Some studies have found that a high calcium intake, mainly through supplements, was linked with a higher risk for prostate cancer. This was especially true for prostate cancers that were more aggressive.

Both men and women should try to take in recommended levels of calcium, mainly through food sources. Dairy products are excellent sources of calcium, as are some leafy vegetables and greens. People who get much of their calcium from dairy products may want to select low-fat or fat-free choices to reduce their intake of saturated fat.

Some health problems can keep calcium from being absorbed from the stomach. Poor vitamin D intake and inactivity decrease calcium absorption. Low stomach acid can cause calcium carbonate to be poorly absorbed, although it doesn't affect other forms of calcium the same way. For those who either have low stomach acid or who take medicine to block stomach acid, calcium citrate absorbs better.

Those who have kidney stones, kidney failure, or high parathyroid levels should talk with their doctors before taking calcium supplements. People who are having treatment for cancer should talk to their doctors or cancer team before taking vitamins, minerals, or other supplements that might interact with the cancer drugs prescribed.

Relying on this type of treatment alone and avoiding or delaying conventional medical care for cancer may have serious health consequences.

Vitamin K

Other common name(s):

the clotting vitamin, vitamin K1, vitamin K2, vitamin K3

Scientific/medical name(s):

2-methyl-1,4-naphthoquinone, 4-amino-2-methyl-1-naphthol hydrochloride, AquaMEPHYTON®, Konakion®, menadiol diphosphate, menadiol acetate, menadiol sodium phosphate, menadione, menaquinones, menatetrenone, Mephyton®, MK-4, MK-7, phylloquinone, phytomenadione, phytonadione

Description

Vitamin K is a group name for a number of related compounds. Each form can serve as an essential nutrient needed by the liver in order to form proteins that promote blood clotting and prevent abnormal bleeding. There are 3 basic forms of vitamin K: K1, K2, and K3, but there are subtypes as well. Vitamin K1 (phylloquinone or phytonadione) is a natural nutrient found in green leafy vegetables, such as lettuce, cabbage, collard greens, broccoli, spinach, and turnip greens. Okra, asparagus, prunes, and avocado also contain vitamin K1. Some oils, such as soybean oil, olive oil, and canola oil, contain smaller amounts of vitamin K1. Vitamin K2 (menaquinones or MKs) in foods are mostly in the form of MK4 and MK7. Small amounts of MK4 can be found in animal products such as meats and dairy products. MK7 is a natural product of bacteria that live in the human lower intestine. MK7 is also found in certain fermented products, such as cheese, and in large amounts in the Japanese soy product known as natto. Cooking does not remove the vitamin or stop its action. Vitamin K3 (menadione) is a potent synthetic (man-made) form of vitamin K that is not used in humans.

Overview

Vitamin K is necessary for normal blood clotting and may be needed for other activities. The human body gets vitamin K from certain foods and bacteria that normally live in the intestines. Available scientific evidence does not support the use of vitamin K supplements for cancer treatment or prevention. However, a small clinical trial found that a vitamin K2 compound seemed to reduce the risk that liver cancer would come back after surgery. Later studies have not shown much effect, and vitamin K is now being tested along with other drugs to find out if that will help more.

How is it promoted for use?

Vitamin K is known mainly as a blood-clotting nutrient. But some alternative medical practitioners claim that vitamin K3 is also an anti-cancer agent. Others claim that high doses of vitamin K3 and vitamin C supplements can slow or stop tumor growth when taken together. Available scientific evidence does not support these claims.

Vitamin K is also promoted as an ingredient in some cosmetic or herbal creams to lighten redness caused by broken blood vessels and to treat skin irritation (burns and sunburns) and scarring. Promoters recommend that these so-called "clarifying" creams be applied to the skin every day for several weeks.

What does it involve?

Healthy adults who eat plenty of leafy green vegetables generally get all the vitamin K they need from natural sources. The Food and Nutrition Board considers 90 micrograms per day for women and 120 micrograms per day for men to be an adequate intake (1 milligram is equal to 1,000 micrograms). Foods usually provide the body with about half of the normal supply of the vitamin, while intestinal bacteria produce the rest.

Only those who have symptoms of a vitamin K deficiency may need to take supplements. The signs of a deficiency include abnormal or excessive bleeding, such as frequent nosebleeds, abnormally bleeding gums, heavy menstruation, or blood in the urine or stool. People with symptoms like these should see their doctors, because these signs may also signal more serious problems. A deficiency may result from extended treatment with antibiotics, which can kill the bacteria that produce vitamin K; liver damage; or intestinal disorders such as celiac disease, cystic fibrosis, or removal of part of the intestine. Chronic malnutrition, including alcoholism, can also cause vitamin K deficiency.

Newborns lack the bacteria in their intestines to produce vitamin K and may be at risk of serious bleeding. Newborns are usually given vitamin K supplements, either as a shot or by mouth, while in the hospital. Babies who get supplements in the hospital do not need any more after they leave unless they have intestinal problems.

Phytonadione or phylloquinone (vitamin K1) and menaquinone (vitamin K2) supplements are available in tablet and capsule form from health food stores and on the Internet. Some K2 (menaquinone or MK) subtypes are sold by name. The U.S. Food and Drug Administration (FDA) does not allow menadione (vitamin K3) to be sold as a dietary supplement for humans, although it is allowed in some feeds for farm animals.

What is the history behind it?

In 1935, a Danish scientist named Henrik Dam published his findings about a previously unknown substance that was required to form clots. It was named for the Danish and German words for clotting, Koagulations-vitamin. Since then, studies in the lab and on animals have tried to learn whether vitamin K plays a role in preventing the development or spread of cancer. To date, there is no convincing evidence available to suggest that it does.

Researchers in the 1990s began to worry about a possible link between childhood cancers, especially leukemia, and injections of vitamin K supplements in newborns. Further study has found no link between cancer and vitamin K injections. The American Academy of Pediatrics' latest recommendations advise that all newborns should receive the injection to prevent serious bleeding.

What is the evidence?

There is overwhelming scientific evidence that vitamin K is required for normal blood clotting.

Some studies have suggested a link between low blood levels of this vitamin K and increased risk for some types of cancer. A large European epidemiologic study published in 2008 found higher risk of prostate cancer in men with low intake of some forms of vitamin K. But people who take in plenty of vitamin K usually get it from fruits and vegetables. This means that people who get lots of vitamin K from foods are more likely to take in many other vitamins and phytochemicals that can affect cancer risk. In some cases, vitamin K may be given credit for benefits that are actually due to other compounds that appear in the same foods. So studies like this, which only look at large groups of people, may not be very useful for looking at the effects of vitamin K intake.

There have been some studies examining whether menadione (vitamin K3) can help overcome cancer cells' resistance to certain types of chemotherapy drugs. Results in lab animals and cell cultures are mixed, but there is no evidence available of significant effects in humans yet.

An animal study done in 1998 found that a man-made form of vitamin K known as compound 5 might slow the growth of cancer cells. Since then, several more studies have suggested that this and other forms of vitamin K might be active against cancer cells in laboratory dishes or mice. Laboratory studies are pinpointing how these compounds work, with some finding that certain vitamin compounds seemed very active against liver cancer. Some clinical trials on humans have already begun. The goal is to find out whether vitamin K compounds can help in cancer treatment or prevention.

A small Phase I clinical trial in California tested different doses of intravenous vitamin K3 in people with advanced cancer. The patients did not improve. In that study, several patients also had allergic reactions, especially at higher doses.

A 2006 clinical trial suggested that menatetrenone (also called MK4, a subtype of the vitamin K2 group) might be able to reduce recurrence of liver cancer after surgery. This was a small pilot study, and later studies did not show much effect. MK4 is now being tested along with other drugs after surgery for liver cancer, with some promising early results.

A small clinical trial from Japan suggested that vitamin K lowers the risk of developing liver cancer among women with cirrhosis. Further study is needed.

There are also studies of MK4 that suggest it may decrease osteoporosis and possibly fracture. Some studies suggest that vitamin K might have a role in keeping bones strong, especially in older people. Studies suggest that it has an effect, but it is unclear whether it is the most effective way to prevent bone loss and fracture. Further research is needed to confirm this and, if confirmed, to find out the best way to use the vitamin.

Two small human studies looked at vitamin K cream and gel to see whether it helped bruises to fade faster after laser treatments. Researchers had people apply the vitamin K twice a day to one side of their body and the cream or gel without the vitamin (placebo) to the other. Bruises seemed to go away a bit more quickly on the side of the body on which vitamin K was used. Still, the effect of the vitamin cream or gel was not very different from placebo. More studies still need to be done to find out whether this is a worthwhile treatment and if so, how to best use it.

Are there any possible problems or complications?

Natural vitamin K is considered safe as a normal part of a daily diet. Supplements of the vitamin are not usually needed unless a doctor finds a problem that requires them.

Injectable formulas of vitamin K (vitamin K3) can cause allergic reactions and some toxic effects. During clinical trials of vitamin K3, some patients experienced flushing of the face, numbness in their arms and legs, chest pain, and shortness of breath. Immediate severe allergies can cause shock and even death. Sometimes a milder reaction happens in the form of an itchy bump that comes up where the injection was given. The bump can take over a month to go away and can sometimes cause scarring. Injectable vitamin K can also cause red blood cells to be destroyed in some people.

Rarely, allergic rashes can develop after using vitamin K creams on the skin.

Those who are on the blood-thinning medication warfarin (Coumadin) should know that vitamin K can make warfarin less effective. Talk with your health care provider before taking vitamin K supplements or changing the amount of vitamin K you take in through foods. The effects of Vitamin K from fermented sources (MK7), such as cheese and natto, can last days longer than vitamin K from plants. Talk to your doctor about how these foods might affect your lab test results if you are taking warfarin.

Pregnant women who are on anti-seizure medicines should get vitamin K supplements for 2 to 4 weeks before giving birth because of increased risk of bleeding in the newborn. Otherwise, the safety of vitamin K supplements during pregnancy is not known, although the amount of vitamin K from foods is thought to be safe.

Relying on this type of treatment alone and avoiding or delaying conventional medical care for cancer may have serious health consequences.

Vitamin E

Scientific/medical name(s):

alpha-tocopherol, tocopherols, tocotrienols

Description

Vitamin E is an essential nutrient the human body needs to function normally. The term vitamin E actually represents a group of fat-soluble substances that work as antioxidants in the body. (Antioxidants block the action of free radicals (activated oxygen molecules that can damage cells).) There are 8 natural forms of vitamin E. The most important one to the human body is alpha-tocopherol.

The main sources of vitamin E in the diet are vegetable oils (especially safflower oil, sunflower oil, and cottonseed oil), green leafy vegetables, nuts, cereals, meats, egg yolks, wheat germ, and whole-wheat products.

Vitamin E deficiency is rare and occurs almost exclusively in people with an inherited or acquired condition that impairs their ability to absorb this vitamin. Symptoms of vitamin E deficiency include muscle weakness, visual problems (especially at night), immune system changes, and a poor sense of balance. Over a long time, vitamin E deficiency may progress to blindness, heart disease, nerve damage, and impaired thinking. Supplements are usually only necessary or recommended for people with vitamin E deficiency or a condition that puts them at risk for this deficiency.

Overview

There is some evidence suggesting a protective effect of vitamin E against prostate, bladder, and colorectal cancer, but more research is needed. Most clinical studies show that vitamin E supplements do not have any overall health benefit or any beneficial effect on heart disease or cancer in general, and may even lead to increased risk of heart failure. Available scientific evidence does not support claims that vitamin E significantly affects the growth of cancers that have already formed.

How is it promoted for use?

Some proponents claim vitamin E plays a role in protecting the body against cancer by bolstering the immune system and by preventing damage to DNA and other important parts of cells. Some also believe the vitamin can increase the effectiveness of some chemotherapy drugs and may reduce some side effects of chemotherapy and radiation therapy. But others believe high doses of vitamin E might interfere with the effectiveness of radiation therapy and chemotherapy.

Proponents also claim that vitamin E supplements protect against heart attacks by preventing a build-up of harmful cholesterol and blood clots in the blood. There are also claims that vitamin E eases the inflammation associated with arthritis, speeds wound healing in people who have suffered burns or have had surgery, and slows the progress of Parkinson's disease and Alzheimer's disease. Some say that it may help prevent or treat eye problems like cataracts and age-related macular degeneration. Vitamin E is also used to protect against the effects of pollution and overexposure to the sun.

What does it involve?

A balanced diet normally gives the body the amount vitamin E it needs, especially a diet low in fat and high in green leafy vegetables and fiber from grains and cereals. The recommended daily allowance (RDA) of vitamin E for adults is 15 milligrams per day from food, with 19 milligrams per day recommended for women who are breast-feeding. (Vitamin E is often measured as IU (International Units); one milligram equals 1.5 IU.) This recommendation was revised by the National Academy of Science (NAS) in April 2000. It also set the upper limit of intake from supplements at 1,000 milligrams (1,500 IU) per day.

Vitamin E supplements are taken as capsules, with a typical dose being 400 IU per day.

What is the history behind it?

Since the 1940s, researchers and others have thought that vitamin E might prevent heart disease. Researchers have observed that people who have cancer often also have low levels of vitamin E in their blood. More recently, several clinical trials have been completed (and others are still in progress) comparing the risk of cancer among volunteers randomly assigned to get either vitamin E supplements or a placebo ("look alike" treatment).

What is the evidence?

Most of the evidence for the preventive effects of antioxidants like vitamin E comes from animal studies and from observational epidemiologic studies that use surveys to estimate how much vitamin E a person gets from food and supplements. The most reliable studies on this issue are controlled clinical trials, such as a large 1994 study of antioxidant vitamins and cancer conducted by the National Cancer Institute (NCI) and the National Public Health Institute of Finland. The study was designed to find out whether antioxidant vitamins in high doses (50 milligrams daily) could reduce the incidence of lung cancer, other types of cancer, and other illnesses among 29,000 male smokers. The study found no beneficial effect of vitamin E supplements on lung cancer incidence. It found lower rates of prostate and colorectal cancer, but higher rates of bladder, stomach, and other types of cancer in those who got high doses of vitamin E.

A 2000 National Academy of Sciences report stated that there was not enough evidence to support claims that taking high doses of antioxidants (such as vitamins C and E, selenium, and beta carotene) can prevent chronic diseases.

Individual clinical trials can sometimes provide misleading results because of variation in research methods or random statistical variation. Because of this, researchers often analyze the combined data from many studies. This is called meta-analysis. A meta-analysis published in 2005 combined data from 19 clinical trials that looked at vitamin E supplements. The results showed that vitamin E supplements, overall, do not lower the risk of heart disease or cancer, and that people who got the placebo actually lived slightly longer than those getting the supplements.

Another large clinical trial published in 2005 also found no risk reduction for heart disease or cancer overall. It even suggested that heart failure was slightly more common in people taking vitamin E. And a 2007 review of 68 studies of antioxidant vitamin supplements found that people taking vitamin E supplements had a shorter life expectancy than those who did not take these supplements.

The Women’s Health Study began in 1991. This clinical trial looked at whether vitamin E could protect women from heart attack, stroke, or cancer. Results published in 2005 showed that vitamin E had no effect on cardiovascular disease or on the most common cancers in women: lung, breast, and colorectal cancers.

The SELECT (Selenium and Vitamin E Cancer Prevention Trial) looked at the effect of vitamin E alone or in combination with selenium (an antioxidant mineral) on prostate cancer risk. (See our document Selenium for more information.) The SELECT was expected to end in 2013. But a preliminary analysis in 2008 showed no difference in prostate cancer risk between the groups taking the vitamin E supplement and the placebo, and the results suggested that vitamin E might even have slightly increased the risk of developing prostate cancer. The selenium supplement did not appear to be beneficial, either, and early results suggested that it might slightly increase the risk of developing diabetes. Because of these possible risks, the researchers advised participants to stop taking the supplements, but follow-up tests will continue for several years to learn more about long-term effects of the supplements.

Vitamin E has also been studied in clinical trials of people who have had one cancer in order to see if it could keep the cancer from coming back (cancer recurrence) or prevent a second, new cancer. Clinical trials of people with head and neck cancer found it did not reduce the risk of recurrence or the risk of a second cancer.

Many researchers and clinicians believe that taking high doses of antioxidant vitamins may change how well radiation therapy and some chemotherapy drugs work, but they often disagree as to whether the changes are beneficial or harmful. Some researchers and doctors think antioxidants like vitamin E might reduce side effects or even improve effectiveness of radiation or chemotherapy. Others are concerned that antioxidants will reduce effectiveness of these treatments. Very few studies have yet been done in humans to test these theories, and there is no clear consensus yet. Most oncologists advise their patients to avoid antioxidant vitamin and mineral supplements during treatment, but some surveys suggest this advice is often ignored by patients. Further studies are needed to resolve this important question.

Are there any possible problems or complications?

This product is sold as a dietary supplement in the United States. Unlike drugs (which must be tested before being sold), the companies that make supplements are not required to prove to the Food and Drug Administration that their supplements are safe or effective, as long as they don't claim the supplements can prevent, treat, or cure any specific disease.

Some such products may not contain the amount of the herb or substance that is on the label, and some may include other substances (contaminants). Actual amounts per dose may vary between brands or even between different batches of the same brand. In 2007, the FDA wrote new rules to improve the quality of manufacturing for dietary supplements and the proper listing of supplement ingredients. But these rules do not address the safety of the ingredients or their effects on health.

Most such supplements have not been tested to find out if they interact with medicines, foods, or other herbs and supplements. Even though some reports of interactions and harmful effects may be published, full studies of interactions and effects are not often available. Because of these limitations, any information on ill effects and interactions below should be considered incomplete.

Vitamin E supplements found in multivitamins are generally considered safe as long as the levels do not exceed the recommended dietary allowance (RDA). Large doses of vitamin E (more than 533 milligrams or 800 IU) taken over a long time can cause nausea, vomiting, stomach pain, and diarrhea. High doses of supplements may also slow the way the body absorbs vitamins A, D, and K, causing deficiencies of these vitamins. It may also cause heart problems and change the blood's ability to form clots. Megadoses of vitamin E supplements are not advised for people who are taking blood-thinning medicines, like warfarin (Coumadin®), because the supplements might counteract the effects of the drugs.

People with cancer should talk to their doctor before taking vitamin E or any other vitamin supplements, especially while they are getting chemotherapy or radiation therapy. Relying on this type of treatment alone and avoiding or delaying conventional medical care for cancer may have serious health consequences.

Vitamin D

Other common name(s):

calcitriol, calciferol, ergocalciferol (vitamin D2), cholecalciferol (vitamin D3), 1,25-D, the sunshine vitamin

Scientific/medical name(s):

1,25 dihydroxycholecalciferol, 25 hydroxycholecalciferol, 1,25 dihydroxyvitamin D

Description

Vitamin D is an important vitamin the body needs to regulate the amount of calcium and phosphorus in the body. It is best known for its role in using calcium to help build bones and keep them strong. Vitamin D affects many other tissues in the body, including the kidneys, intestines, and parathyroid glands.

Vitamin D is found in salmon, mackerel, tuna, and sardines, as well as in cod liver oil. Beef liver, cheese, and egg yolks contain small amounts. Most of the milk supply in the United States has vitamin D added to it, as do some breakfast cereals, orange juices, and milk substitutes (such as soy milk). Experts note that vitamin D acts more like a hormone than a vitamin, in part because the body can make its own vitamin D if the skin gets enough ultraviolet (UV) rays from sunlight.

Overview

Vitamin D is needed to keep a balance between calcium and phosphorus in the body. It controls how much of these nutrients are absorbed from foods or even taken from bones. While known for its role in building bones and keeping them strong, the exact function of vitamin D in other cells and organs is not fully known. It has a role in nerve, muscle, and immune function, and affects inflammation as well as cell growth and death.

After fairly brief exposure to sunlight, the body can make vitamin D for several hours. But the amount of sun it takes to make enough vitamin D depends on several factors (see "What does it involve?"). Because UV light exposure is linked to skin cancer and other diseases, safety is a concern when sunlight is used to meet vitamin D requirements. Most people can get enough vitamin D from foods and supplements, if they are used properly. Foods and vitamin D supplements have the advantage of not causing skin cancer and other unwanted effects on the skin that can be caused by UV light.

Some studies suggest that risk of developing some types of cancer is lower for people who have higher levels of vitamin D in the body. But more studies are needed to find out whether vitamin D is the reason for this decreased risk, or if there is another reason. If there is a link, researchers would still have to find out whether vitamin D deficiency raises a person's cancer risk. They would also need to know whether taking in more vitamin D than the recommended daily value lowers this risk. The possible role of vitamin D in treating cancer is still being studied.

How is it promoted for use?

Vitamin D is promoted by mainstream clinicians mainly for its role in balancing calcium and phosphorus and keeping bones healthy. Some other practitioners further claim that vitamin D is an immune system booster that can be used to prevent many problems, including autism, type I diabetes, schizophrenia, mood disorders, infectious diseases, cancer, and other illnesses. Others say it helps with weight loss. In orthomolecular medicine and some other forms of alternative medicine, large doses of vitamin D may be used along with other vitamins to treat cancer (see Orthomolecular Medicine). Researchers are also looking into using Vitamin D along with chemotherapy as a possible part of standard cancer treatment.

What does it involve?

The body can make vitamin D after exposure to UV rays or it can be obtained through some foods or supplements. The amount of vitamin D made when the skin is exposed to sunlight depends on several factors, including:

• Age
• Skin color
• How much skin is exposed
• Time of year
• Time of day
• Cloud cover
• Smog, dust, or haze
• Length of exposure
• Geographic location

Latitudes further away from the equator do not get much UV light through the earth's atmosphere in the winter months. This can be a problem for people who live in the northern United States and Canada and who do not take in much vitamin D in foods. Darker-skinned people need somewhat longer UV exposures to trigger their bodies to make vitamin D, and older people do not make as much vitamin D as younger people in response to sunlight. Sunscreen also blocks UV rays, which reduces the body's ability to produce vitamin D.

Even in a sunny climate, sunlight's effects can be hard to predict. One study looked at 93 adults in Hawaii who reported several hours of sun exposure each week for at least 3 months. The researchers found that half of them had low vitamin D levels in their blood. Closer analysis showed no predictable link between vitamin D levels and age, lightest or darkest skin colors, or hours of sun exposure without sunscreen. Clearly, there is no "one size fits all" prescription for a reliable minimum amount of sun exposure to meet the vitamin D requirements of every person.

The body stores several forms of vitamin D. Vitamin D3 is the form that is made in the skin. Vitamin D2 (calciferol) or D3 (cholecalciferol) can be absorbed from food. All must be changed into 25 hydroxyvitamin D (25 hydroxycholecalciferol), a form that can last for several weeks in the blood. This is the vitamin D level that doctors generally check.

The liver and kidneys change vitamin D into calcitriol (also called 1,25 dihydroxycholecalciferol or 1,25 dihydroxyvitamin D), which helps the intestine absorb more calcium and phosphorus.

The Institute of Medicine was able to set a recommended daily allowance (RDA) for vitamin D in 2010. The RDA of vitamin D for infants, children, and men and women up through age 70 is 15 micrograms (equal to 600 International Units or IU) per day. The RDA is 20 micrograms (800 IU) a day for adults older than 70. The safe upper limit for adults was set at 100 micrograms (4,000 IU) per day.

Blood tests can now measure the body's stores of vitamin D, and many people have unexpectedly low levels. For those with low levels, there are questions about how much vitamin D it takes to raise the body's stores of it to healthy levels.

Because vitamin D occurs naturally in very few foods, some adults may not get enough from their everyday diet. After vitamin D started being added to milk and other breakfast foods, many people have been able to get more of it. For instance, 1 cup of fortified milk contains half of the current adequate intake (AI) of vitamin D (see below) for an adult between the ages of 19 and 50. But that same cup supplies only one-quarter of the AI for an adult aged 51 to 70, and about one-sixth of the AI for a person 71 or older.

This means that fortified foods and/or vitamin D supplements may be needed by some people:

• People age 50 and older, whose skin cannot make as much vitamin D and/or whose kidneys are less able to convert vitamin D to its active form
• People with limited sun exposure; for instance, those who are homebound, who live in northern areas such as New England and Alaska, women who wear robes and head coverings for religious reasons, and people whose work prevents sun exposure, if they are unable to consume enough vitamin D in foods
• Adults with darker skin. Some studies suggest that older adults with dark skin, especially women, are at even higher risk of vitamin D deficiency if they do not consume enough vitamin D in foods
• People who do not absorb fat well. This is linked to several medical conditions:
• Deficiency of pancreatic enzymes
• Crohn's disease
• Cystic fibrosis
• Sprue or celiac disease (gluten intolerance)
• Certain types of liver disease
• Surgical removal of all or part of the stomach or intestine
• Children and teens who are not exposed to sun and who do not drink at least 2 cups of fortified milk per day
• People who are lactose intolerant, allergic to milk, or who avoid milk products for any reason
• Infants who are breast-fed only. Formula is fortified with vitamin D. An infant who consumes 2 cups of formula per day takes in adequate vitamin D.
• People who are overweight or obese. The more body fat a person has, the more vitamin D is needed to increase blood levels of the vitamin

Vitamin D supplements are most often taken as pills although cod liver oil is also still used. Supplements are available at drugstores, grocery stores, health food stores, and on the Internet.

What is the history behind it?

Rickets, a disease of weak bones and other deformities, was first described in the mid-1600s as a major problem among city children. Even though there were reports that rickets could be cured by sunbathing or cod liver oil, the disease was still widespread in northern Europe in the early twentieth century. After vitamin A was discovered in 1913 by Elmer McCollum as a cure for night blindness, a British doctor named Edward Mellanby induced rickets in dogs and then cured the condition using cod liver oil. He assumed that the vitamin A in the cod liver oil had cured the dogs. To test Mellanby's theory, McCollum devised a way to inactivate the vitamin A in cod liver oil. As expected, the oil no longer cured night blindness. To nearly everyone's surprise, however, it still cured rickets, which proved that another substance besides vitamin A was responsible. McCollum published these findings in 1922, calling this substance vitamin D. Soon after, a program to add vitamin D to milk was started in the United States, and rickets was nearly wiped out. Cod liver oil has remained a home remedy ever since.

Even though vitamin D was named and put to wide use, scientists in the early twentieth century knew almost nothing about what it was or how it worked. It took years of study and discoveries by a number of researchers to learn that there were several forms of vitamin D, and how they work in the body.

German researcher Adolf Windaus first discovered 3 forms of the vitamin, which he called D1, D2, and D3. (Because it was later learned that the product Windaus named vitamin D1 was a mixture of compounds rather than a pure vitamin D product, the term D1 is no longer used.) In the early 1950s, Arvid Carlsson found that vitamin D can remove calcium from the bones when the body needs it for other uses. Ragnar Nicolaysen, a dietary researcher, discovered that the amount of calcium absorbed from food is guided by an internal factor that tells the intestine how much the body needs. In 1975, another researcher named Mark Haussler confirmed that the intestines have a receptor protein that only binds to active vitamin D.

Today, vitamin D is still added to most milk sold in the United States, although it is not added to all milk products like cheese and ice cream. Some companies also add it to cereal, soy milk, rice milk, and orange juice, usually along with calcium. It is now understood that rickets is the product of long-standing and severe vitamin D deficiency, and that milder cases of deficiency may have no symptoms.

Since a few studies in the early 2000s have suggested higher levels of vitamin D may be linked to lower cancer risk, more studies have begun to look at this possibility.

What is the evidence?

Laboratory and animal studies and observational epidemiologic studies suggest that higher levels of vitamin D in the body may be linked to lower cancer risk. Observational studies only look at people without changing anything they do, so it is hard to know the role of the vitamin D.

The studies suggest that the risk for some forms of cancer is lower in those who get more calcium and vitamin D (which may include vitamin D from foods as well as sunlight). Higher vitamin D levels in the blood have also been linked to lower risk for some types of cancer, especially colorectal cancers. One researcher who analyzed 60 such studies noted that calcium intake appeared more protective than vitamin D against colon and rectal cancer. Because of the way vitamin D works with calcium, it may be hard to separate these effects.

Vitamin D seemed to be a bigger factor in a study of more than 3,000 adults (mostly men) who had colonoscopies between 1994 and 1997 to look for polyps or cancer. Those with the highest vitamin D intake were less likely to have advanced cancer than those with low intake. Although all of this sounds promising, observational epidemiologic studies cannot prove that other unknown factors may have caused the outcome of lower cancer risk.

Randomized clinical trials, which offer much stronger evidence than observational studies, are also studying the role vitamin D may play in cancer prevention. A Women's Health Initiative study published in 2006 put more than 36,000 menopausal women into 2 groups: half got vitamin D with calcium and half got a placebo (sham pill). After 7 years, the researchers looked at colorectal cancer risk in the 2 groups. Cancer risk was not lower in the group that took vitamin D. Critics of the study noted that the dose given (400 IU per day) may have been too low to make a difference, and that many women were not taking their pills at all. The average vitamin D and calcium intake of the women at the start of the study was also about twice as high as the national average, and close to the doses used in the study. And finally, women in the study were allowed to take extra vitamin D and calcium if they wished. This means that many women who were thought to be on placebo may have taken the same or higher doses as those who were in the test group. These factors may have limited the ability of the study to find any differences. Interestingly, colorectal cancer risk was lower in women who had higher levels of vitamin D in their blood at the start of the study. Researchers will keep watching the women until late 2010, so there may be more information at that time. A report on this study from 2009 showed no difference in death rates between the test group (women given vitamin D and calcium supplements) and those who were not given them.

A 4-year study published in 2007 looked at 1,179 healthy women over age 55 who were randomly chosen from rural Nebraska. The researchers gave a third of the women 1,400 to 1,500 milligrams of calcium each day. Another third received calcium plus 1,100 IU of vitamin D3 each day, while the rest got a placebo. The women who took calcium and vitamin D had significantly less risk for all types of cancer combined, as did the women who had higher vitamin D levels when the study started. This sounds promising, but it was only one study, so it is hard to be certain the vitamin D and calcium caused the difference. It is possible that other differences between the groups may have accounted for the lower cancer rates. Before this information can be used to recommend increased supplements of vitamin D and calcium, it needs to be confirmed by other studies. For one thing, it needs to be shown that the findings hold true in other groups of people. For another, doctors would want to know if these higher doses raise the risk of other problems, and whether there are unexpected side effects. For instance, more kidney stones have been reported in women taking vitamin D and calcium.

Well-designed clinical trials are needed to confirm whether low levels of vitamin D raise cancer risk and to find out if taking more vitamin D (with or without extra calcium) reduces cancer risk. Until such studies are completed, it is too early to advise people to take vitamin D supplements for cancer prevention.

The International Agency for Research on Cancer, a part of the World Health Organization, reviewed this topic and concluded in a 2008 report that vitamin D may reduce risk of colorectal cancer, but not prostate cancer, and that the evidence is weak regarding a link with breast cancer.

A 2010 analysis of data from 10 studies did not find any association of vitamin D levels and 6 less common types of cancer -- endometrial, esophageal, gastric, kidney, non-Hodgkin lymphoma, and ovarian. And, people with the highest vitamin D levels seemed to have an higher, rather than lower, chance of developing pancreatic cancer.

Some researchers are interested in whether vitamin D can play a role in cancer treatment. A few small studies have looked at vitamin D along with standard treatment for prostate cancer. In one study of 16 men with metastatic prostate cancer, 1 in 4 had less bone pain and 1 in 3 had stronger muscles after taking 2,000 IU of vitamin D each day for 12 weeks. However, nearly half of the patients were deficient in vitamin D at the start of the study, which could have affected the results.

Another study looked at the effects of vitamin D3 on blood levels of prostate-specific antigen (PSA) in men whose prostate cancer had come back after treatment. PSA is a substance produced by normal and cancerous prostate cells, and high levels are considered to be a sign of cancer growth. After treatment with radiation or surgery, the men took daily doses of vitamin D3 for a period of between 6 and 15 months. The researchers observed that in 6 of 7 patients, their PSA levels increased more slowly than before they started the vitamins. However, the men began to lose calcium in their urine, which limited the amount of vitamin D they could safely take. This was a small pilot study that called for further testing.

A 2003 study of 22 men with recurrent prostate cancer used larger weekly doses of vitamin D3. The researchers observed that the weekly dose was safe. However, while the rate of PSA increase in men slowed to some extent, more studies are needed to find out whether vitamin D has a significant role in slowing the growth of prostate cancer. Studies could also help find out if it helps people live longer or feel better.

Women who are vitamin D–deficient give birth to children with very little vitamin D in their bodies. In addition, past testing has shown that human breast milk contains very little vitamin D. This finding has led to the recommendation that infants who are fed only breast milk be given vitamin D supplements. However, recent small early studies in breast-feeding women have found that women with high blood levels of vitamin D have adequate amounts in their breast milk. In order to reach these levels, though, researchers had to give the women very high doses of vitamin D each day. More research is needed to find out about safety and side effects, use of blood tests to measure vitamin D status, and the healthiest blood levels of the vitamin.

Researchers are also testing whether vitamin D can help make some chemotherapy drugs work better. Lab studies and early human studies in prostate cancer were encouraging, so a more careful randomized, double blind clinical trial was done. The findings that came out in 2008 did not show that taxotere plus vitamin D worked any better than taxotere alone in prolonging the lives of men with advanced prostate cancer.

Researchers are also testing deltanoids—compounds chemically related to vitamin D—for cancer prevention and for treatment. These are being tested alone and in combination with other cancer drugs.

Vitamin D can prevent and treat some bone problems such as rickets in children and osteomalacia in adults. Vitamin D deficiency, which is often seen in older people, can lead to osteoporosis and is linked to an increased risk for broken hips. Studies of the effect of vitamin D supplements on hip fracture risk among older people have had conflicting results. More information is needed before any recommendations can be made for older people at risk of hip fracture.

Although low vitamin D levels seem to be linked to several diseases, further study is needed to learn whether the disease causes the low levels of vitamin D, the vitamin deficiency increases the risk for disease, or there is some other relationship between the two.

Are there any possible problems or complications?

This product is sold as a dietary supplement in the United States. Unlike companies that produce drugs (which must be tested before being sold), the companies that make supplements are not required to prove to the Food and Drug Administration that their supplements are safe or effective, as long as they don't claim the supplements can prevent, treat, or cure any specific disease.

Some such products may not contain the amount of the herb or substance that is on the label, and some may include other substances (contaminants). Actual amounts per dose may vary between brands or even between different batches of the same brand. In 2007, the FDA wrote new rules to improve the quality of manufacturing for dietary supplements and the proper listing of supplement ingredients. But these rules do not address the safety of the ingredients or their effects on health.

Most such supplements have not been tested to find out if they interact with medicines, foods, or other herbs and supplements. Even though some reports of interactions and harmful effects may be published, full studies of interactions and effects are not often available. Because of these limitations, any information on ill effects and interactions below should be considered incomplete.

Vitamin D is considered safe as part of a normal healthy diet. Too much vitamin D can cause nausea, vomiting, poor appetite, constipation, weakness, and weight loss. It can also raise blood calcium levels, causing changes in mental status such as confusion. High blood calcium can also cause abnormal heart rhythms. Too much vitamin D over a long time can cause depression, headaches, sleepiness, and weakness, as well as calcium and bone loss. It can also cause the arteries and other soft tissues of the body (such as kidneys, heart, lungs) to become hardened and lined with layers of calcium, a condition known as calcinosis.

Getting vitamin D through sunlight may not work for some and may cause problems for others. Besides the danger of sunburn, exposure to ultraviolet light can cause skin cancer; wrinkled, sagging skin; damage to the eyes, including cataracts; and can impair the immune system. Reflective surfaces make UV exposure more intense and can worsen these effects. Water, snow, and sand reflect the most. While sun exposure can cause other problems, it has never been reported to produce toxic levels of vitamin D. Vitamin D from foods is also unlikely to cause toxic effects unless large amounts of cod liver oil are used. Vitamin D toxicity is much more likely to occur as a result of taking too many supplements. Vitamin D toxicity has also been caused by foods that were incorrectly fortified (foods or milk that had accidentally been mixed with far more vitamin D than intended).

Laxatives, steroids, and anti-cholesterol drugs like cholestyramine (Questran, Locholest) and colestipol (Colestid) may lower the amount of vitamin D you can absorb. Vitamin D should be taken several hours before or after these drugs. Anti-seizure drugs and rifampin (an anti-tuberculosis drug) can lower your vitamin D levels. Too much vitamin D may raise calcium levels, which can cause abnormal heart rhythms if you are taking digoxin. People with low parathyroid function may have a higher risk of abnormally high calcium levels when taking vitamin D. This problem can be worsened by certain diuretics (water pills).

If you take vitamin D with calcium, note that calcium can keep certain drugs from being absorbed. Always talk with your doctor and pharmacist about all the herbs, supplements, and medicines you are taking. Relying on this type of treatment alone and avoiding or delaying conventional medical care for cancer may have serious health consequences.

Vitamin C

Scientific/medical name(s):

ascorbic acid, ascorbate

Description

Vitamin C is an essential vitamin the human body needs to function well. It is a water-soluble vitamin that cannot be made by the body, and must be obtained from foods or other sources. Vitamin C is found in abundance in citrus fruits such as oranges, grapefruit, and lemons, and in green leafy vegetables, potatoes, strawberries, bell peppers, and cantaloupe.

Overview

Vitamin C is necessary for healthy skin, scar tissue, tendons, ligaments, bones, cartilage, and blood vessels, and for the healing of wounds and injuries. A shortage of vitamin C causes scurvy. Fortunately, vitamin C deficiency is very rare among people who eat a reasonably balanced diet.

Many studies have shown a connection between eating foods rich in vitamin C, such as fruits and vegetables, and a reduced risk of cancer. On the other hand, evidence indicates that vitamin C supplements do not reduce cancer risk. This suggests that the activity of fruits and vegetables in preventing cancer is due to a combination of many vitamins and other phytochemicals and not to vitamin C alone (see Phytochemicals). Clinical trials of high doses vitamin C as a treatment for cancer have not shown any benefit. High doses of vitamin C can cause a number of side effects.

How is it promoted for use?

Vitamin C is an antioxidant, a compound that blocks the action of activated oxygen molecules, known as free radicals, that can damage cells. Vitamin C is thought by some to enhance the immune system by stimulating the activities of natural killer cells (a type of white blood cell) and anti-cancer agents. Some claim that the vitamin can prevent a variety of cancers from developing, including lung, prostate, bladder, breast, cervical, intestinal, esophageal, stomach, pancreatic, and salivary gland cancers, as well as leukemia and non-Hodgkin's lymphoma. Vitamin C is also said to prevent tumors from spreading, help the body heal after cancer surgery, enhance the effects of certain anti-cancer drugs, and reduce the toxic effects of other drugs used in chemotherapy. These claims are being studied.

Some practitioners recommend high doses of vitamin C supplements to protect against and treat colds, although the value of this approach has not been proven.

What does it involve?

Vitamin C is water-soluble, which means that the body uses what it needs and eliminates the rest. The recommended dietary allowance (RDA) of vitamin C for women is 75 mg/day (slightly more is recommended for those who are pregnant or breast-feeding) and for men is 90 mg/day. These recommendations were revised by the Food and Nutrition Board of the National Academy of Sciences (NAS) in April 2000. The recent NAS report set the upper limit from both food and supplements at 2,000 mg (2 grams) per day.

Vitamin C supplements are available in powder or chewable pill form at grocery stores, health food stores, drug stores, and over the Internet. Recommended dosages vary by manufacturer. Some of these supplements contain vitamin C only, whereas others are multivitamin supplements that contain variable amounts of vitamin C. Vitamin C is commonly added to foods and drinks. Some of these, such as breakfast cereals, typically contain no more than the RDA of vitamin C, but some other drinks and foods contain considerably more.

What is the history behind it?

First identified in 1928 by Nobel Prize winner Albert Szent-Gyorgyi, vitamin C has been studied ever since for its nutritional and disease-preventing role. In 1970, two-time Nobel Prize winner Linus Pauling advocated large doses of vitamin C (1,000 mg/day or more) to prevent colds and reduce their severity.

In 1979, in a book called Vitamin C and Cancer, Pauling claimed that high doses of vitamin C could also be effective against cancer. His claim was based on a 1976 study he did with a Scottish physician in which 100 patients with advanced cancer were given 10,000 mg of vitamin C. The study concluded that the patients treated with vitamin C survived 3 to 4 times longer than patients not given the supplements. The Pauling study has been criticized by the National Cancer Institute for being poorly designed, and later studies done at the Mayo Clinic found that advanced cancer patients given the same dose of vitamin C did not survive any longer than those not given the supplement. However, the Mayo Clinic trials have also been criticized for not fully addressing all the issues related to the effects of vitamin C, which still left questions about whether or not it is effective in treating cancer.

What is the evidence?

Many scientific studies have shown that eating a diet high in fruits and vegetables (containing vitamin C) significantly reduces the risk of developing cancers of the pancreas, esophagus, larynx, mouth, stomach, colon and rectum, breast, cervix, and lungs. Many of these studies show that a high intake of vitamin C from food sources has about a two-fold protective effect when compared to a low intake of the vitamin. Likewise, people with higher blood levels of vitamin C tend to have a lesser risk of developing cancer than do people with lower levels. Vitamin C is known to be an antioxidant. An antioxidant is a compound that blocks the action of activated oxygen molecules, known as free radicals, that can damage cells.

However, studies that observed large groups or people and clinical trials of vitamin C supplements have not shown the same strong protective effects against cancer. Apparently, vitamin C is most helpful when it is eaten naturally in fruits and vegetables because of the other active ingredients in the food. A 2007 review of 68 clinical studies of antioxidant vitamin supplements concluded that taking vitamin C supplements had no detectable effect on lifespan.

The 2000 National Academy of Sciences report stated that there is not enough evidence to support claims that taking high doses of antioxidants (such as vitamins C and E, selenium, and beta carotene) can prevent chronic diseases. Some oncologists believe that taking high doses of antioxidant vitamins may actually interfere with the effectiveness of radiation and some chemotherapy drugs. This conclusion is based on their understanding of the biochemical mechanisms through which these treatments kill cancer cells. However, no clinical trials have yet been done in humans to test this theory. More research is needed to evaluate this question. Although high doses of vitamin C have been suggested as a cancer treatment, the available evidence from clinical trials has not shown any benefit.

At this time, it is hard to say how each nutrient or nutrient combination affects a person’s risk of cancer. On the other hand, studies of large groups of people have shown that those whose diets are high in vegetables and low in animal fat, meat, and/or calories have lower risks for some of the most common types of cancer. Until more is known about this, the American Cancer Society recommends eating a variety of healthful foods--with most of them coming from plant sources--rather than relying on supplements.

Choose whole grains over refined grains and sugars, and limit high-fat and processed meats. Select foods that help maintain a healthy weight. It is also important to engage in moderate to vigorous physical activity for 30 to 60 minutes 5 or more days per week. For most people, this will help keep weight under control, reduce risk of some cancers, and reap many other health benefits. While it is best to get vitamins and minerals from foods, supplements may be helpful for some people, such as pregnant women, women of childbearing age, and people with restricted food intakes. If a supplement is taken, the best choice for most people is a balanced multivitamin/mineral supplement that contains no more than 100% of the "Daily Value" of most nutrients.

Are there any possible problems or complications?

This product is sold as a dietary supplement in the United States. Unlike drugs (which must be tested before being allowed to be sold), the companies that make supplements are not required to prove to the Food and Drug Administration that their supplements are safe or effective, as long as they don't claim the supplements can prevent, treat, or cure any specific disease.

Some such products may not contain the amount of the herb or substance that is written on the label, and some may include other substances (contaminants). Actual amounts per dose may vary between brands or even between different batches of the same brand.

Most such supplements have not been tested to find out if they interact with medicines, foods, or other herbs and supplements. Even though some reports of interactions and harmful effects may be published, full studies of interactions and effects are not often available. Because of these limitations, any information on ill effects and interactions below should be considered incomplete.

Vitamin C supplements are generally considered safe unless doses are higher than 2,000 mg/day. Doses higher than 1,000 mg (1 gram) can cause headaches, diarrhea, nausea, heartburn, stomach cramps, and possibly kidney stones. Vitamin C can also increase the amount of iron the body absorbs, which is generally only a problem for those with hematochromatosis (too much iron in the body).

Most oncologists routinely recommend that people with cancer avoid gram-size doses of vitamin C during treatment. People with cancer should talk to their doctor before taking vitamin C or other vitamin supplements.

Vitamin B Complex

Other common name(s):

B vitamins; vitamins B1, B2, B3, B5, B6, B7, B9, and B12

Scientific/medical name(s):

thiamine (B1), riboflavin (B2), niacin (B3), pantothenic acid (B5), pyridoxine (B6), biotin (B7), folic acid or folate (B9), cobalamin (B12)

Description

B vitamins are essential for growth, development, and a variety of other bodily functions. They play a major role in the activities of enzymes, proteins that regulate chemical reactions in the body, which are important in turning food into energy and other needed substances. B vitamins are found in plant and animal food sources.

Overview

B vitamins are an important part of the diet and are needed to help avoid many health problems. But, with the exception of vitamin B9 (folic acid), there is not enough scientific evidence to know whether B vitamins can reduce the risk of cancer.

People with low intake of folic acid are at increased risk for certain types of cancer. A diet rich in vegetables containing this vitamin, and perhaps a daily multivitamin supplement containing the recommended daily value of folic acid is recommended by some experts in cancer prevention. (See our separate document, Folic Acid, for more information.)

Available scientific evidence does not support claims that any B vitamin is an effective treatment for people who already have cancer.

How is it promoted for use?

Scientists know that B vitamins are part of many important bodily functions:

• Vitamin B1 (thiamin) and vitamin B2 (riboflavin) help the body produce energy and affect enzymes that influence the muscles, nerves, and heart.
• Vitamin B3 (niacin) has a role in energy production in cells and helps keep the skin, nervous system, and digestive system healthy.
• Vitamin B5 (pantothenic acid) influences normal growth and development.
• Vitamin B6 (pyridoxine) helps the body break down protein and helps maintain the health of red blood cells, the nervous system, and parts of the immune system.
• Vitamin B7 (biotin) helps break down protein and carbohydrates and helps the body make hormones.
• Vitamin B9 (folic acid) helps the cells in the body make and maintain DNA and is important in the production of red blood cells.
• Vitamin B12 (cobalamin) plays a role in the body's growth and development. It also has a part in producing blood cells, nervous system function, and how the body uses folic acid and carbohydrates.

Deficiency of certain B vitamins can cause anemia, tiredness, loss of appetite, abdominal pain, depression, numbness and tingling in the arms and legs, muscle cramps, respiratory infections, hair loss, eczema, poor growth in children, and birth defects.

Some alternative medical practitioners claim that deficiencies in B vitamins weaken the immune system and make the body vulnerable to cancer. They recommend high doses of B vitamins as treatments for people with cancer. Many researchers are studying the relationships between vitamin intake and risk of developing certain cancers.

What does it involve?

Nutritionists maintain that a balanced diet that includes 5 daily servings of fruits and vegetables, as well as grains, gives most people with all the B vitamins they need. Only small amounts of these vitamins are needed to reach the recommended dietary intakes. But many people do not eat enough fruits, vegetables, or other healthy foods to get the recommended amounts. The National Academies of Science (NAS) recommends that adults over the age of 50 take B vitamin supplements, or eat foods enriched with these vitamins, in order to prevent deficiency, which is common in this age group.

Women who are pregnant or breast-feeding need more folic acid than others. The Public Health Service recommends that women of childbearing age who can become pregnant should consume at least 400 micrograms of folic acid daily through dietary supplements and fortified foods, in addition to a diet containing folate-rich foods, to help prevent certain birth defects in their children.

Food sources of B vitamins:

• B1 and B2 are found in cereals and whole grains. B1 is also found in potatoes, pork, seafood, liver, and kidney beans. B2 is found in enriched bread, dairy products, liver, and green leafy vegetables.
• B3 is found in liver, fish, chicken, lean red meat, nuts, whole grains, and dried beans.
• B5 is found in almost all foods.
• B6 is found in fish, liver, pork, chicken, potatoes, wheat germ, bananas, and dried beans.
• B7 is made by intestinal bacteria and is also in peanuts, liver, egg yolks, bananas, mushrooms, watermelon, and grapefruit.
• B9 is in green leafy vegetables, liver, citrus fruits, mushrooms, nuts, peas, dried beans, and wheat bread.
• B12 is found in eggs, meat, poultry, shellfish, milk, and milk products.

Supplements that contain several B vitamins, usually in combination with other nutrients, are sold in grocery stores, health food stores, and over the Internet in pill form. Dosages vary by manufacturer.

What is the history behind it?

While the diseases caused by vitamin deficiencies have been known for centuries, just about all of the B vitamins were discovered in the early 1900s. Since then, B vitamins have been studied to determine how they affect the human body.

As their importance and functions were clarified, the US government began recommending daily intake levels to promote and maintain good health. The current recommended levels are known as dietary reference intakes (DRIs).

Research on the possible role of some B vitamins in preventing cancer began in the last few decades.

What is the evidence?

The limited data on B vitamins and cancer come mainly from animal studies and observational epidemiologic studies. These types of studies are not as strong as randomized controlled clinical trials and must be interpreted with caution.

There is some evidence from observational epidemiologic studies that increased intake of vitamin B9 (folic acid) is linked to a lower risk of colon cancer, especially in people who are vitamin deficient, such as those who drink excessive amounts of alcohol. Evidence of effects on breast cancer and other types of cancer has been mixed.

Most observational epidemiologic studies have also shown a link between intake of vitamin B6 (as well as blood levels of this vitamin) and lower risks of colorectal cancer. Possible links between other B vitamins and cancer risk have not been studied as extensively or have been studied with mixed results.

Only a few randomized clinical trials of B vitamin supplements have been done. Most of these studies reported that supplements did not reduce cancer risk. In one recent study, people given folate and vitamin B6 supplements were more likely to develop and die of cancer than people taking a placebo pill. It is still unclear whether taking in more B vitamins will help protect against cancer or increase cancer risk. Some scientists have proposed that inherited differences in to the way a person's body uses B vitamins influence whether these supplements will harm or help a person, and that some day it will be possible to provide a personalized recommendation that might lower cancer risk.

Even if some B vitamins prove to be helpful in preventing certain cancers, it does not mean that B vitamins would be useful in treating cancers. In fact, some experts have cautioned that certain B vitamins, such as thiamine and folic acid, might actually make it easier for established tumors to grow. This is not well proven, but caution is advised when considering taking large doses of these vitamins.

At this time, it is hard to say how each nutrient or nutrient combination affects a person’s risk of cancer. On the other hand, studies of large groups of people have shown that those whose diets are high in vegetables and low in animal fat, meat, and/or calories have lower risks for some of the most common types of cancer. Until more is known about this, the American Cancer Society recommends eating a variety of healthy foods -- with most of them coming from plant sources -- rather than relying on supplements.

While it is best to get vitamins and minerals from foods, supplements may be helpful for some people. If a supplement is taken, the best choice for most people is a balanced multivitamin/mineral supplement that contains no more than 100% of the "Daily Value" of most nutrients. Pregnant women, women of childbearing age, and people with restricted food intakes should speak with their doctors about supplements containing higher levels of certain vitamins.

Are there any possible problems or complications?

This product is sold as a dietary supplement in the United States. Unlike drugs (which must be tested before being sold), the companies that make supplements are not required to prove to the Food and Drug Administration that their supplements are safe or effective, as long as they don't claim the supplements can prevent, treat, or cure any specific disease.

Some such products may not contain the amount of the herb or substance that is on the label, and some may include other substances (contaminants). Actual amounts per dose may vary between brands or even between different batches of the same brand. In 2007, the FDA wrote new rules to improve the quality of manufacturing for dietary supplements and the proper listing of supplement ingredients. But these rules do not address the safety of the ingredients or their effects on health.

Most such supplements have not been tested to find out if they interact with medicines, foods, or other herbs and supplements. Even though some reports of interactions and harmful effects may be published, full studies of interactions and effects are not often available. Because of these limitations, any information on ill effects and interactions below should be considered incomplete.

B vitamins are water-soluble, meaning that any excess intake is largely excreted in the urine. Supplements containing B vitamins are generally thought to be safe but still should not be taken in very large doses. Possible side effects include gout, high blood sugar levels, and skin problems. Overdoses can lead to heart and liver problems. Rarely, large doses of vitamin B3 (niacin) supplements can cause blurred vision, nausea, vomiting, and can make stomach ulcers worse. High doses of folic acid supplements may interfere with at least one chemotherapy drug, methotrexate, and other medicines like it. Always tell your doctor and pharmacist about any supplements and herbs you are taking.

Relying on the use of B vitamins alone and avoiding or delaying conventional medical care for cancer may have serious health consequences.

Vitamin A and Beta Carotene

Scientific/medical name(s):

Retinol, retinoic acid, retinoids

Description

Vitamin A is a nutrient that is vital to growth and development. Vitamin A is obtained in two ways:

1. As vitamin A from animal sources such as liver, fish oils, egg yolks, and dairy products As beta carotene from many fruits and vegetables (such as carrots, broccoli, spinach, squash, peaches, and apricots) which the body converts to retinol (a type of vitamin A) in the small intestine.
2. Vitamin A is stored in the liver until needed by the body. Vitamin A and closely related molecules are also known as retinoids.

Overview

Vitamin A supplements have not been proven to prevent cancer in humans. But clinical studies are being done to explore the role of vitamin A and other retinoids in cancer prevention and treatment. High doses of vitamin A are toxic, and long-term use of high-dose supplements may increase the risk of lung cancer among people at high risk, like smokers.

How is it promoted for use?

Vitamin A is essential for normal growth, bone development, reproduction, and vision. It is used to help maintain healthy skin and mucous membranes, like the ones that line the nose and mouth. This helps protect against infections in the respiratory, digestive, and urinary tracts.

Some research suggests that vitamin A and some other retinoids are able to change cancer cells and can also prevent normal cells from becoming cancer. Retinoids are prescribed as a standard medical treatment for some rare types of cancer or pre-cancerous conditions.

Some alternative healers recommend taking carotenoid supplements as part of a regimen to "cleanse" or "detoxify" the body, especially the liver. Others suggest that beta carotene can be used to treat certain types of cancer.

What does it involve?

Vitamin A is absorbed from dietary animal fats, from dietary supplements, and in the form of beta carotene, which is found in some fruits and vegetables and converted to vitamin A by the body. Vitamin A is stored in the liver, so it does not need to be consumed every day.

The best way to get this vitamin is to eat a well-balanced diet. People who eat a balanced diet of fruits, vegetables, dairy products, and animal fats usually get enough vitamin A and beta carotene for good health, but supplements are available. The recommended daily allowance (RDA) of vitamin A is 2,310 IU (0.7 milligrams) per day for adult women (more for women who are pregnant or breastfeeding) and 3,000 IU (0.9 milligrams) per day for adult men.

What is the history behind it?

The discovery of vitamin A dates back to research from the early twentieth century. Over the past twenty years, vitamin A has been extensively studied as a cancer-fighting nutrient in laboratory, animal, and population studies. In addition to studies of vitamin A and cancer prevention, related retinoids have also been evaluated in laboratory studies and in human clinical trials.

Several studies based on dietary surveys of large numbers of people have concluded that eating foods rich in vitamin A is linked to a lower risk of certain types of cancer. But it is not clear whether the protective effect was due to vitamin A or to other helpful substances in these foods.

What is the evidence?

Vitamin A deficiency can cause a lowered resistance to infection, poor night vision or even blindness, poor growth in children, weak bones and teeth, inflamed eyes, diarrhea, and poor appetite. It is rare in developed countries.

Some animal studies have found that vitamin A and other retinoids may enhance the immune system, slow tumor growth, shrink tumors, and make some cancer treatments work better. Some laboratory, animal, and human studies have found that certain retinoids may also inhibit cancer development.

Studies of vitamin A's possible role in cancer prevention have been generally disappointing. Clinical trials have found that vitamin A supplements do not lower the risk for lung cancer in smokers and actually increased their risk for dying of lung cancer and heart disease. Studies of overall health and longevity found no benefit to taking vitamin A supplements, and the US Institute of Medicine does not recommend use of these supplements by the general public. Studies on vitamin A and other types of cancer have been mixed. There have been no consistent findings showing a lower risk of cancers of the stomach, intestines, skin, breast, cervix, bladder, or prostate due to vitamin A in the diet.

The use of vitamin A supplements has also not been proven to reduce cancer risk in humans. It appears that the combination of micronutrients in fruits, vegetables, legumes, and grains is more likely to be helpful than individual vitamins.

A 2007 review of 68 studies of vitamin supplements concluded that people taking beta carotene or vitamin A supplements had a shorter life expectancy than those who did not take these supplements.

Synthetic retinoids that are more potent than natural vitamin A or beta carotene have shown some ability to reverse pre-cancers in the cervix, mouth, throat, and skin. They also may help prevent new tumors in people who have already been treated for these forms of cancer. But more clinical research is needed. Several clinical trials involving retinoids have been completed and others are still going on.

Retinoids are not currently used as a cancer treatment, with one notable exception. A relatively rare type of leukemia, promyelocytic leukemia, often responds to a combination of retinoic acid (a retinoid) and chemotherapy. Patients with this form of leukemia get high doses of a pure form of retinoic acid (derived from Vitamin A) under medical supervision. Treatment of promyelocytic leukemia does not include use of non-prescription vitamin A supplements or dietary changes intended to increase intake of this vitamin.

Studies of other types of cancer such as lung cancer, head and neck cancer, and melanoma found that vitamin A supplements are not helpful as treatments. Some oncologists are concerned that vitamin A and other vitamins that act as antioxidants may even make chemotherapy and radiation therapy less effective when taken during treatment. This is why many oncologists recommend that their patients not take such antioxidant supplements until their treatment is complete.

Are there any possible problems or complications?

This product is sold as a dietary supplement in the United States. Unlike companies that produce drugs (which must provide the FDA with results of detailed testing showing their product is safe and effective before the drug is approved for sale), the companies that make supplements do not have to show evidence of safety or health benefits to the FDA before selling their products. Supplement products without any reliable scientific evidence of health benefits may still be sold as long as the companies selling them do not claim the supplements can prevent, treat, or cure any specific disease. Some such products may not contain the amount of the herb or substance that is written on the label, and some may include other substances (contaminants). The FDA has written new rules to improve the quality of manufacturing processes for dietary supplements and the accurate listing of supplement ingredients. But, the new rules do not address the safety of supplement ingredients or their effects on health when proper manufacturing techniques are used. 

Most such supplements have not been tested to find out if they interact with medicines, foods, or other herbs and supplements. Even though some reports of interactions and harmful effects may be published, full studies of interactions and effects are not often available. Because of these limitations, any information on ill effects and interactions below should be considered incomplete.

High doses of vitamin A supplements can cause nausea, vomiting, diarrhea, loss of appetite, tiredness, headaches, dizziness, blurred vision, poor muscle coordination, itchiness and scaling of the skin, bone pain, hair loss, irregular menstruation in women, osteoporosis, and temporary or permanent liver damage. They can also cause birth defects if taken during pregnancy. Relying on this type of treatment alone and avoiding or delaying conventional medical care for cancer may have serious health consequences.