Vitamin C and Cancer
A study just published in the British medical journal The Lancet found that even a small increase in vitamin C intake can have a significant impact on mortality from cancer and other diseases.
Dr. Kay-Tee Khaw from the University of Cambridge School of Clinical Medicine and colleagues evaluated survey results from close to 20,000 participants in the European Prospective Investigation into Cancer and Nutrition study.
They measured the plasma concentrations of vitamin C for each participant over a four-year period and compared this data with eventual death rates. They found that those participants with the highest concentrations of plasma vitamin C had the lowest overall mortality rates.
In fact, a 20 percent reduction in "all-cause" mortality risk was associated with an increase in vitamin C intake of only 50 grams a day from fruits and vegetables.
"Our findings suggest that an increase in dietary intake of foods rich in ascorbic acid [vitamin A] might have benefits for cardiovascular disease and all-cause mortality," Khaw wrote. "[Our findings] add to the large amount of evidence that lends support to the health benefits of fruit and vegetable intake."
Vitamin C and Cancer
The claim that vitamin C is specifically useful in the treatment of cancer is largely attributable to Linus Pauling, Ph.D., the Nobel laureate who first reported in 1976 that cancer patients treated with megadoses of vitamin C survived three- to four-times longer than patients who did not take the vitamin. Pauling and his associate, Scottish surgeon Ewan Cameron, reported in the Proceedings of the National Academy of Sciences that megadoses of vitamin C represented a significant advance in the prevention and treatment of cancer.
But their conclusions were assailed almost immediately as being too broad, as well as being based on a faulty clinical trial design. For example, in 1982, Dr. William DeWys, the chief of the clinical investigations branch of the National Cancer Institute, pointed out that the vitamin C and control groups in the Pauling/Cameron study had not been properly matched by stage of disease, functional ability, weight loss and sites of metastasis.
He also asserted that the patients given vitamin C had less advanced disease than those in the placebo group, thus skewing the results in favor of the vitamin supplement.
In 1978, the Mayo Clinic conducted the first of three clinical trials to test the vitamin C claims of Pauling and Cameron, taking great pains to ensure that patients in both the vitamin C and placebo groups were equally matched. Importantly, they found no statistical differences in disease progression or eventual mortality between either group-in all three of their trials.
Overall Health Benefits
Nonetheless, a significant body of research has shown that healthy adults can benefit in many ways from a daily intake of 100 to 200 mg of vitamin C. For example, Dr. Mark Levine of the National Institute of Diabetes and Digestive and Kidney Diseases, writing in the Journal of the American Medical Association, suggested that adults need about 200 mg of vitamin C daily. This is approximately the amount contained in five servings of fruits and vegetables.
"Our work reinforces the health message that healthy people should be eating five servings of a variety of fruits and vegetables every day. You'll get adequate vitamin C and you have the potential benefit of preventing disease, especially certain cancers," Levine wrote.
He said that healthy people are better off eating fruits and vegetables rather than relying on supplements because absorption of the vitamin in supplements varies widely, depending on manufacturing methods and the dose taken. Daily doses of 200 mg of vitamin C from supplements do not decrease the incidence of certain kinds of cancer.
The current Recommended Daily Allowance (RDA) for vitamin C is 90 mg/day for men and 75 mg/day for women. (It is recommended that smokers add an additional 35 mg/day to their respective rates.) The U.S. Department of Agriculture estimates that 39 percent of men and 43 percent of women fall short of these recommended requirements.
Take Caution
A poll released by the American Institute for Cancer Research found that 54 percent of Americans above the age of 65 are taking vitamins with the specific aim of reducing their risk of cancer, (as are 24 percent of those aged 55 to 64).
But, while eating while eating plenty of fruits and vegetables has been shown in hundreds of studies to lower the risk of developing cancer, there is no strong evidence that taking just vitamin supplements provides the same benefits.
The bottom line is that there is simply no substitute for a healthy, well-balanced diet. Most vitamin and mineral supplements are not harmful in appropriate doses-and many may certainly have specific, albeit limited benefits. But claims that a particular vitamin or mineral supplement can single-handedly prevent cancer from occurring are clearly not warranted, and possibly even dangerous.
SOURCES:
The Lancet, March 3, 2001; 357:657-663
Proceedings of the National Academy of Sciences, 1976; 73:3685-3689
Nutrition Forum, 2000; 17(01); 3-5
American Institute for Cancer Research (http://www.aicr.org)
Journal of the American Medical Association, April 21, 1999; (281)15
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