There is an old Sufi story in which Mulla Nasrudin is in his yard, in front of his house throwing corn. A man passing by is puzzled and stops. "Mulla Nasrudin", he asks, "why are you throwing corn all over your yard?" "It keeps the tigers away," he replies. "But there are no tigers around here." "Well it works then, doesn't it?" the mulla replies.
This parable is similar to our health behavior. We are advised by "experts" (often people selling us something) who cite epidemiological studies that would suggest that if you take some product you'll prevent some malady. The problem with most of these studies is they cannot demonstrate a cause effect relation between an intervention (like a vitamin) and an outcome (lets say not getting cancer).
Approximately one-half of adult Americans used dietary supplements in the year 2000, with sales of $20 billion that year. This represents a shift from using vitamins and minerals to prevent deficiency states, to using them in the absence of malnourishment, to promote wellness and prevent disease. Unfortunately, we have no good data that indicates this makes sense. In fact, the results of randomized clinical trials suggest vitamin and mineral use can be harmful.
A large, well designed, and well conducted study published this week in the Archives of Internal Medicine reported the results of the Iowa Women's Health Study. The investigators assessed the relation between vitamin and mineral supplementation and mortality in 38,772 women with a mean age of 61.6 years. They found that the use of multivitamins, B6, folic acid, magnesium, zinc, iron and copper was associated with an increased risk of mortality. The association was strongest for supplemental iron. The association for iron was dose dependent, that is, the higher the dose, the more deaths observed.
A second study published this week in the Journal of the American Medical Association demonstrated that vitamin E supplementation not only does not protect against prostate cancer, it may increase risk. Men receiving a common dose of vitamin E (400IU) had a 17% increased risk for prostate cancer compared to men who received placebo.
In my recent blog, That Which Does Not Kill Us Makes Us Stronger: Why You Should Throw Out Your Vitamins, I discussed the negative effect of antioxidant vitamins before exercise. The JAMA paper cited above contributes to a growing body of evidence indicating that vitamin E, vitamin A, and beta-carotene can be harmful.
These negative reports are particularly concerning given that those who take supplements show a greater range of healthy lifestyle factors (non-smokers, low-fat diets, exercisers) than non users. So even in the context of good preventive health practices, vitamins can impair health.
If one thinks about evolution, and how we've eaten throughout our existence, it is not shocking to read these reports. We have never taken in such quantities of these nutrients in our history. The vitamins and minerals were always packaged in foods that dictated how how they were assimilated into our system. More is not better. It seems to be worse.
We must wonder how much of our life is spent throwing corn, and what our own personal tigers are.
Vitamin takers were stunned to learn that their supplements