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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 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 does 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.
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 ordered
from our toll-free number (1-800-ACS-2345).
References
Bjelakovic, G, et al 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, et al. Failure of
high-dose vitamin C (ascorbic acid) therapy to benefit patients with
advanced cancer. A controlled trial. N Engl J Med.
1979;301(13):687-90.
Food and Nutrition Board, Institute of Medicine. Dietary
Reference Intakes for Vitamin C, Vitamin E, Selenium, and Carotenoids.
Washington, DC: National Academy Press; 2000. Also available at:
http://www.nap.edu/openbook/0309069351/html/. Accessed May 7, 2007.
Hwang MY. How much vitamin C do you need? JAMA.
1999;281:1415.
Kushi, L.H., Byers, T., Doyle, C., et al. 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:
A Cancer Journal for Clinicians 2006; 56, 254–281.
Labriola D, Livingston R. Possible interactions between
dietary antioxidants and chemotherapy. Oncology.
1999;13:1003-1008.
Levine M, Rumsey SC, Daruwala R, Park JB, Wang Y. Criteria
and recommendations for vitamin C intake. JAMA.
1999;281:1415-1423.
Memorial Sloan Kettering Cancer Center. Vitamin C. Available
at: http://www.mskcc.org/mskcc/html/69413.cfm. Accessed May 7, 2007.
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(3):137-41.
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.
Vickers, A. Alternative Cancer Cures: "Unproven" or
"Disproven"? CA Cancer
J Clin 2004 54: 110-118.
Willett WC and Stampfer MJ. What vitamins should I be taking,
doctor? N Engl J Med.
2001; 345: 1819-24.
Zhang S, Hunter DJ, Forman MR, et al. Dietary carotenoids and
vitamins A, C, and E and risk of breast cancer. J Natl Cancer Inst.
1999;91:547-556.
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.
Revised: 06/19/2007
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