B vitamin supplementation questioned

A fascinating study was published last week in JAMA about supplementation with B vitamins (specifically folate, vitamin B6 and B12) among more than 6,000 patients with coronary artery disease.

This was a randomized, placebo-controlled trial conducted in Norway from 1998 to 2005. Patients were randomly assigned to folate/B6/B12, folate/B12, B6 alone or placebo. This is in Norway where they do not supplement food with B vitamins. Surprisingly (to me at least), the patients who received B12 and folate had higher cancer incidence rates (HR=1.21, CI, 1.07-1.79) and higher overall mortality (HR=1.18, CI 1.04-1.33).

The authors note the increased cancers were driven largely by lung cancer. This is similar to the beta carotene in that the vitamin supplementation that investigators thought might prevent cancer (or mortality) actually increased negative outcomes. This continues to give me pause before endorsing vitamin supplementation routinely for my patients (note that the doses in this study were not much higher than the recommended daily allowances [0.8 mg daily of folate and 0.4 mg daily of B12]), and are far below the "super dose" vitamins many patients receive based on Internet research, non-traditional health care providers and other less evidence-based sources.

This study also brings some concern to mind over the U.S. policy to supplement grains with folate to prevent neural tube defects as well. (See the accompanying editorial that discusses this in more depth.) I'm quite curious to see where this goes. Whatever the final decisions about U.S. supplementation policies, this is a very important study to be aware of.