Vitamins and Antioxidants
Impact on Cancer
Over the years, there have been many cohort and case studies that seemed to demonstrate that taking various antioxidant vitamin supplements decreases the incidence of various kinds of cancer. However starting around 1996, the evidence of benefits reported in these studies started unravelling. Two randomized, double-blind, placebo-controlled studies (references 7 and 8) did not show any benefit due to consumption of beta-carotene, and indicated that in certain situations, beta-carotene may actually be detrimental.
In the sudy in reference 7, 22,000 male physicians were enrolled (1982) in a double-blind randomized study, taking 50 mg of beta carotene on alternate days, or a placebo. the age span was 40 to 84 years of age. 11 percent were smokers, and 39% were former smokers. In the group taking beta-carotene, 1273 men had any malignant neoplasm (a tumor that is malignant and tends to spread to other parts of the body) by the end of 1995. In comparison, the number among the placebo takers was 1293. These two numbers are statistically equivalent, showing that the risk reduction in taking beta-carotene was between 0.91 to 1.06 (Margin of Error). Evidently, in this study, beta-carotene produced neither benefit nor harm! The same conclusions were deduced for cardiovascular disease, and for death from all causes.
Reference 8 presents a similar type of study involving 18,000 workers at high risk for lung cancer: smokers, former smokers, and workers exposed to asbestos. The treatment was 30 mg of beta-carotene per day, and 25,000 IU of retinol (vitamin A). After an average of 4 years, 388 new cases of lung cancer were diagnosed. The group receiving the active treatment had an increased risk! The risk ratio for contracting lung cancer was 1.28 (1.04 to 1.57 Margin of Error), compared to the placebo group. This is the first time, to my knowledge, that a vitamin supplement was implicated in increasing the risk of an illness.
Reference 5 provides information on one of many more studies (randomized, double-blind) that likewise show no benefit for vitamin consumption on cancer, the same result as for heart disease. In the study, 21,000 men and women, aged 40 to 80, were randomly assigned to a placebo group, or to supplemenation of 900 IU vitamin E, 250 mg vitamin C and 20 mg beta-carotene daily, for a 5 year treatment period. The risk ratio for any cancer, while taking the supplements, was determined to be 0.98 compared to patients taking a placebo (0.89 to 1.08 Margin of Error) - essentially no difference.
Reference 9 goes further - it presents results that seem to indicate that vitamin supplementation can actually be detrimental to one's health! Its authors reviewed all randomized trials comparing antioxidant supplements with placebo for prevention of gastrointestinal cancers. They identified 14 studies, with a total of 170,525 participants. The trials looked at effects of supplementation with beta-carotene, vitamins A, C, E, and selenium (alone or in combination) versus placebo on esophageal, gastric, colorectal, pancreatic, and liver cancer incidences. In the seven high-quality trials (a total of 131,727 participants), one type of analysis showed that antioxidants significantly increase mortality. The risk ratio they determined was 1.06 (1.02-1.10 Margin of Error). Another type of meta-analysis determined a similar risk ratio of 1.06, but the Margin of Error (0.98-1.15) includes a null effect (risk ratio of 1.0). In particular, combination of beta-carotene with vitamin A increased mortality by a factor of 1.29 (1.14 to 1.45 Margin of Error).
Reference 10 is an editorial that provides a summary of the situation in the year 2000. They conclude that while fruit and vegetable consumption result in lower rates of heart disease and several types of cancer, there is no evidence that extracting a few of the components and consuming them in supplementation form provides any benefit. Their conclusion is even more relevant today!
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