Worth checking out:
Enough Is Enough: Stop Wasting Money on Vitamin and Mineral Supplements
With respect to multivitamins, the studies published in this issue and previous trials indicate no substantial health benefit. This evidence, combined with biological considerations, suggests that any effect, either beneficial or harmful, is probably small. As we learned from voluminous trial data on vitamin E, however, clinical trials are not well-suited to identify very small effects, and future trials of multivitamins for chronic disease prevention in well-nourished populations are likely to be futile.
In conclusion, β-carotene, vitamin E, and possibly high doses of vitamin A supplements are harmful. Other antioxidants, folic acid and B vitamins, and multivitamin and mineral supplements are ineffective for preventing mortality or morbidity due to major chronic diseases. Although available evidence does not rule out small benefits or harms or large benefits or harms in a small subgroup of the population, we believe that the case is closed— supplementing the diet of well-nourished adults with (most) mineral or vitamin supplements has no clear benefit and might even be harmful. These vitamins should not be used for chronic disease prevention. Enough is enough.