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.