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.