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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 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
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hope or false promise? CMAJ.
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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.
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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
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Hwang MY. How much vitamin C do you need? JAMA.
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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
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Kushi LH, Byers T, Doyle C, Bandera EV, McCullough M,
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JB. Should supplemental antioxidant administration be avoided during
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Moertel CG, Fleming TR, Creagan ET, Rubin J, O'Connell MJ,
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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
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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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