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Vitamin C

Other common name(s): none

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 of vitamin C taken by mouth as a treatment for cancer have not shown any benefit. Several studies of very high doses given intravenously are currently in progress. 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 free radicals (activated oxygen molecules that can damage cells). Vitamin C is thought by some to enhance the immune system by stimulating the activities of anticancer agents and a type of white blood cell called natural killer cells. Some claim that the vitamin can prevent a variety of cancers from developing, including cancers of the lung, prostate, bladder, breast, cervix, intestine, esophagus, stomach, pancreas, and salivary gland, as well as leukemia and non-Hodgkin lymphoma. Vitamin C is also said to prevent tumors from spreading, help the body heal after cancer surgery, enhance the effects of certain anticancer drugs, and reduce the toxic effects of other drugs used in chemotherapy. Some proponents recommend taking high doses of vitamin C by mouth or intravenously as a cancer treatment.

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 excretes the rest. The recommended dietary allowance (RDA) of vitamin C is 90 milligrams per day for men and 75 milligrams per day for women, with a larger dose recommended for those who are pregnant or breast-feeding. These recommendations were revised by the Food and Nutrition Board of the National Academy of Sciences (NAS) in April 2000. That NAS report set the upper limit for vitamin C from both food and supplements at 2,000 milligrams (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, 2-time Nobel Prize winner Linus Pauling advocated large doses of vitamin C (1,000 milligrams per day or more) to prevent colds and reduce their severity. In a 1979 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 milligrams 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 as 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. There are still questions about whether vitamn C 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 for 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 2-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 lower risk for cancer than people with lower blood levels of vitamin C.

However, observational studies 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. A 2007 review of 68 clinical studies of antioxidant vitamin supplements concluded that taking vitamin C supplements had no detectable effect on life span.

The 2000 NAS 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 therapy 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. Some researchers have suggested that one reason for these results is that when vitamin C is taken by mouth, levels in the body are not high enough to kill cancer cells. Some laboratory studies support this idea, and there are a few case reports of long survival among people who received intravenous vitamin C. On the other hand, critics of this idea have noted that many of the patients in these reports received other conventional or alternative/complementary therapies and that the influence of vitamin C on their cancer is uncertain. In order to help resolve these questions, several clinical trials of high-dose intravenous vitamin C alone or in combination with conventional chemotherapy are currently in progress in patients with several types of cancer.

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.

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 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). Though the FDA has written new rules to improve the quality of manufacturing processes for dietary supplements and the accurate listing of supplement ingredients, these rules do not take full effect until 2010. And, 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.

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

Most oncologists routinely recommend that people with cancer avoid gram-size doses of vitamin C during treatment. People who have cancer should talk to their doctor before taking vitamin C or other vitamin supplements. Relying on this type of treatment alone and avoiding or delaying conventional medical care for cancer may have serious health consequences.

Additional Resources

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).

References

Assouline S, Miller WH. High-dose vitamin C therapy: renewed hope or false promise? CMAJ. 2006;174:956–957.

Bjelakovic G, Nikolova D, Gluud LL, Simonetti RG, Gluud C. Mortality in randomized trials of antioxidant supplements for primary and secondary prevention: systematic review and meta-analysis. JAMA. 2007;297:842-857.

Byers T, Guerrero N. Epidemiologic evidence for vitamin C and vitamin E in cancer prevention. Am J Clin Nutr. 1995;62:1385S-1392S.

Creagan ET, Moertel CG, O'Fallon JR, Schutt AJ, O’Connell MJ, Rubin J, Frytak S. Failure of high-dose vitamin C (ascorbic acid) therapy to benefit patients with advanced cancer. A controlled trial. N Engl J Med. 1979;301:687-690.

Hwang MY. How much vitamin C do you need? JAMA. 1999;281:1460.

Institute of Medicine (US). Panel on Dietary Antioxidants and Related Compounds. Dietary reference intakes for vitamin C, vitamin E, selenium, and carotenoids : a report of the Panel on Dietary Antioxidants and Related Compounds, Subcommittees on Upper Reference Levels of Nutrients and of Interpretation and Use of Dietary Reference Intakes, and the Standing Committee on the Scientific Evaluation of Dietary Reference Intakes, Food and Nutrition Board, Institute of Medicine. Washington, DC: National Academy Press; 2000.

Kushi LH, Byers T, Doyle C, Bandera EV, McCullough M, McTiernan A, Gansler T, Andrews KS, Thun MJ; American Cancer Society 2006 Nutrition and Physical Activity Guidelines Advisory Committee. American Cancer Society guidelines on Nutrition and Physical Activity for cancer prevention: reducing the risk of cancer with healthy food choices and physical activity. CA Cancer J Clin. 2006;56:254-281.

Lawenda BD, Kelly KM, Ladas EJ, Sagar SM, Vickers A, Blumberg JB. Should supplemental antioxidant administration be avoided during chemotherapy and radiation therapy? J Natl Cancer Inst. 2008;100:773-783.

Levine M, Rumsey SC, Daruwala R, Park JB, Wang Y. Criteria and recommendations for vitamin C intake. JAMA. 1999;281:1415-1423.

Moertel CG, Fleming TR, Creagan ET, Rubin J, O'Connell MJ, Ames MM. High-dose vitamin C versus placebo in the treatment of patients with advanced cancer who have had no prior chemotherapy. A randomized double-blind comparison. N Engl J Med. 1985;312:137-141.

Padayatty SJ, Riordan HD, Hewitt SM, Katz A, Hoffer LJ, Levine M. Intravenously administered vitamin C as cancer therapy: three cases. CMAJ. 2006;174:937-942.

Patterson RE, White E, Kristal AR, Neuhouser ML, Potter JD. Vitamin supplements and cancer risk: the epidemiologic evidence. Cancer Causes Control. 1997;8:786-802.

US National Institutes of Health. Pilot trial of intravenous vitamin C in refractory non-Hodgkin lymphoma (NHL). Clinical Trials Web site. http://clinicaltrials.gov/ct2/show/NCT00626444. Accessed September 4, 2008.

US National Institutes of Health. Study of high-dose intravenous (IV) vitamin C treatment in patients with solid tumors. Clinical Trials Web site. http://clinicaltrials.gov/ct2/show/NCT00441207. Accessed September 4, 2008.

US National Institutes of Health. Study of IV decitabine, arsenic trioxide and vitamin C in patients with MDS. Clinical Trials Web site. http://clinicaltrials.gov/ct2/show/NCT00671697. Accessed September 4, 2008.

US National Institutes of Health. Trisenox, ascorbic acid and bortezomib in patients with relapsed/refractory multiple myeloma (AAV). Clinical Trials Web site. http://clinicaltrials.gov/ct2/show/NCT00590603. Accessed September 4, 2008.

Vickers, A. Alternative cancer cures: "unproven" or "disproven"? CA Cancer J Clin. 2004;54:110-118.

Vitamin C. Memorial Sloan-Kettering Cancer Center Web site. http://www.mskcc.org/mskcc/html/69413.cfm. Updated February 28, 2008. Accessed June 6, 2008.

Willett WC, Stampfer MJ. Clinical practice. What vitamins should I be taking, doctor? N Engl J Med. 2001;345:1819-1824.

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: 11/01/2008
Last Revised: 11/01/2008

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