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Dietary Supplements Don’t Prevent Cognitive Decline, CVD, or Infections
Several studies and a meta-analysis all led to the same conclusion — no benefit from supplementation.
In 2006, sales of nutritional supplements exceeded $4.5 billion in the U.S. alone. This year, in several studies, researchers assessed whether supplements — especially with vitamins that are touted as antioxidants — are beneficial.
In one randomized trial, researchers assessed whether long-term vitamin E supplementation slowed cognitive decline among older women (age, 
65 at study entry). At 10 years, global cognitive function did not differ in the vitamin E and placebo groups. In secondary analyses, statistically significant reductions in cognitive decline were seen in several subgroups of vitamin E recipients (i.e., women with low baseline vitamin E intake, women who exercised less than once weekly, and women without diabetes), but these reductions were small and of questionable clinical importance (Journal Watch Jan 4 2007).
Another randomized supplement study involved women with histories of cardiovascular disease or three or more risk factors for cardiovascular disease (CVD). After a mean of 9 years, no reduction was observed in a combined cardiovascular endpoint with vitamin C, vitamin E, or β-carotene supplementation, when taken alone or in combination. In the subgroup of women with histories of CVD, vitamin E was associated with a marginally significant reduction in the endpoint (Journal Watch Sep 27 2007).
In a study from Toronto, nursing home residents were randomized to receive either a multivitamin and mineral supplement or placebo. During 18 months of follow-up, the multivitamin and the placebo groups had similar numbers of infections per patient, infection-free patients, visits to the emergency department, and hospitalizations (Journal Watch Feb 1 2007).
Finally, in a meta-analysis of 68 randomized clinical trials and more than 230,000 patients, researchers assessed the effect of β-carotene, vitamin A, vitamin C, vitamin E, or selenium supplementation, in combination or individually, relative to placebo. Overall, no mortality benefit was seen. When only 47 trials with the highest methodologic quality were examined, a significant increase in mortality risk was noted with supplemental β-carotene, vitamin A, and vitamin E (relative risks, 1.05, 1.16, and 1.04, respectively; Journal Watch Mar 8 2007).
In total, these studies failed to show evidence of health benefit associated with vitamin supplementation across a broad set of clinical endpoints, and potential harm cannot be excluded. Patients should be told that little evidence supports the use of supplements other than for several specific indications (e.g., folic acid for pregnancy). The best advice is to return to mother’s directive — eat your fruits and vegetables.
Published in Journal Watch General Medicine December 28, 2007