Warning on Vitamins and Prostate Cancer

Men who take too many vitamins may (or may not) increase their risk of developing an aggressive form of prostate cancer, according to preliminary evidence published in the Journal of the National Cancer Institute.

Of the dozen or so articles I've read about the study, the best is by Liz Szabo in USA Today.

Right up front, Szabo lets you know that even if the suggested link turns out to be true, the consequences are relatively small. She talks about a "possible link" between heavy use of multi-vitamins and prostate cancer. Then she makes this important point:

If doctors followed 10,000 men for 10 years, there would be about 30 extra cases of advanced prostate cancer and seven or eight extra cases of fatal prostate cancer associated with heavy supplement use, says lead author Michael Leitzmann of the NCI.

This is a variation of the "number needed to treat" figure that should be included with almost any medical story about a proposed new intervention but often isn't. The number need to treat, or NNT, tells you how many people have to follow a particular medical regimen in order to save one person's life or prevent further problems down the line.

For example, you can expect that giving antibiotics to 16 people who have been bitten by a dog will prevent one case of infection. Great for the one person who avoided infection and only a mild nuisance for the 15 others--although you'll never know who was who. (Mike Lemonick had a nice article on the NNT in TIME Magazine in February.)

In the case of vitamins and prostate, Szabo uses it to show that even if the link is true--it's not a huge deal, as these things go.

It may also help explain why the study showed no overall increase in the risk of prostate cancer with more-than-normal multi-vitamin use: the vitamin overdose may not trigger the tumor to grow in the first place, just help it grow faster than it otherwise would have.

Bottomline: go easy on the vitamins, for crying out loud. If you feel you have to take vitamins, one multi-vitamin per day is all you need.

Source: K.A. Lawson, et al. "Multivitamin Use and Risk of Prostate Cancer in the National Institutes of Health–AARP Diet and Health Study;" Journal of the National Cancer Institute 2007 99(10):754-764.