Folic Acid: Friend or Foe?

For the past decade or so, fortifying flour and other foods with small amounts of folic acid has seemed like a no-brainer. After all, science has shown without question that this B vitamin helps prevent neural tube birth defects like spina bifida (and may reduce cleft palate defects as well).

But what’s undeniably good for the fetus and young children may not be so good for older adults. Two recent commentaries in Nutrition Reviews, by Noel Solomons, MD, and Young-In Kim, MD, point out that ever since the fortification efforts started, the rate of colon cancer has inexplicably shot up.

This warning flag comes a scant year or two ago after scientists, basing their theory in part on data from the Nurses Health Study, thought folic acid may actually prevent colon cancer. A 2007 National Institutes of Health-funded clinical trial surprised everyone by debunking that notion and suggesting that a daily 1 mg dose might actually increase the risk of cancer, especially prostate cancer. Researchers theorize that the extra folic acid may fuel the growth of abnormal cells.

Solomons thinks we may need to devise a way to direct this supplement specifically to pregnant women—so we retain the benefit of reduced birth defects—but keep it from affecting the rest of the adult population. So unless you’re pregnant or nursing, you may want to get your folic acid mainly from whole foods (such as wheat germ, lentils, asparagus, spinach, and black beans) and avoid the fortified varieties.