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Vitamin C

Other common name(s): none

Scientific/medical name(s): ascorbic acid, L-ascorbic acid, ascorbate


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, tomatoes, potatoes, strawberries, red or green peppers, and cantaloupe.


Vitamin C is found in many vegetables and fruits, especially oranges, grapefruits, and peppers. Many studies have shown a link between eating foods rich in vitamin C, such as fruits and vegetables, and a reduced risk of cancer. On the other hand, the few studies in which vitamin C has been given as a supplement have not shown a reduced cancer risk.

This suggests that the activity of fruits and vegetables in preventing cancer is due to a combination of many things such as vitamins, fiber, 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 side effects in some people.

How is it promoted for use?

Vitamin C is an antioxidant, a compound that helps block the action of unstable molecules known as free radicals, which 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.

Some practitioners recommend high doses of vitamin C supplements to protect against and treat colds.

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 (with larger amounts for those who are pregnant or breast-feeding) and for men is 90 mg/day. People who smoke and those exposed to secondhand smoke should get more vitamin C. 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 varying 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 a lot more.

What is the history behind it?

By the early 19th century, it was known that a person could prevent and even cure scurvy by using citrus fruits. Finding out exactly why this happened took much longer. Researchers from different countries worked to learn more about it, and vitamin C was first isolated in pure crystalline form in 1927 by Nobel Prize winner Albert Szent-Gyorgyi. He published his paper the next year, calling the substance hexuronic acid. In 1933, the name ascorbic acid was suggested, and vitamin C has been studied ever since for its roles in nutrition and disease prevention.

In the 1970s, 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. 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. At that time, the Mayo Clinic trials were criticized for not fully addressing all the issues related to the effects of vitamin C. But more recent studies still have not shown that supplemental vitamin C is effective in preventing or treating cancer.

What is the evidence?

Small amounts of vitamin C are needed for healthy skin, tendons, ligaments, bones, cartilage, and blood vessels, and for the healing of wounds and injuries. It also helps to body absorb iron from foods. A shortage of vitamin C causes scurvy, a disease marked by fatigue, fragile blood vessels bleeding, which can be fatal if not treated. Vitamin C deficiency is very rare among people who eat a reasonably balanced diet.

Many scientific studies have shown that diets high in fruits and vegetables (many of which contain vitamin C as well as other vitamins, fiber, and phytochemicals) reduce the risk of developing cancers of the pancreas, esophagus, larynx, mouth, stomach, colon and rectum, breast, cervix, and lungs. Many of these studies show people who eat foods to get a high level of vitamin C have about half as much cancer as those who have a low intake of these foods. Likewise, people with higher blood levels of vitamin C tend to have a lesser risk of developing cancer than do people with lower levels, although this likely reflects better overall nutrition rather than supplement use.

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 comes from 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. Still, a 2010 study that looked at several cohort groups noticed that people who took multivitamins had a slightly lower risk of colorectal cancer, although there are several possible explanations for this apparent reduction. But in general, recent studies that have looked at cancer risk have observed that vitamin C supplements are not linked with lower risk of cancer.

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 randomized clinical trials have yet been done in humans to test the effect of Vitamin C supplements during radiation therapy or chemotherapy. 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 plant-based foods and low in red or processed meats 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.

The American Cancer Society recommends that adults should eat at least 2½ cups of fruits and vegetables every day. Choose whole grains over refined grains and sugars, and limit red meats and processed meats. If you drink alcohol, limit your intake – no more than 1 drink per day for women and 2 drinks per day for men. Select foods that help you get to and maintain a healthy weight. Get at least 150 minutes of moderate intensity or 75 minutes of vigorous intensity physical activity each week (or a combination of these), preferably spread throughout the 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 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 C supplements are generally considered safe. Doses higher than 1,000 mg (1 gram) can cause diarrhea, nausea, heartburn, belly pain, and stomach cramps in some people. Vitamin C can also increase the amount of iron the body absorbs, which is generally only a problem for those with hemochromatosis (too much iron in the body). The safe upper limit of vitamin C for adults is considered to be about 2,000 mg (2 grams).

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.

To learn more

More information from your American Cancer Society

The following information on complementary and alternative therapies may also be helpful to you. These materials may be found on our Web site (www.cancer.org) or ordered from our toll-free number (1-800-ACS-2345).


American Cancer Society Guidelines on Nutrition and Physical Activity for Cancer Prevention

Dietary Supplements: What Is Safe?

The ACS Operational Statement on Complementary and Alternative Methods of Cancer Management

Complementary and Alternative Methods and Cancer

Placebo Effect

Learning About New Ways to Treat Cancer

Learning About New Ways to Prevent Cancer


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Note: This information may not cover all possible claims, uses, actions, precautions, side effects or interactions. It is not intended as medical advice, and should not be relied upon as a substitute for consultation with your doctor, who is familiar with your medical situation.

Last Medical Review: 01/16/2013
Last Revised: 01/16/2013