Selenium: Too Much of a Good Thing?

Selenium supplements have been touted as possible cancer fighters, but taken over a long period they might also increase your risk of type-2 diabetes by up to 50 percent, says a recent study in the Annals of Internal Medicine. Scientists wanted to examine whether selenium might prevent diabetes, since previous animal studies suggested it improves glucose metabolism. In an ironic twist, they found that not only does the supplement not prevent diabetes, it may actually cause the disease.

Researchers at England’s Warwick Medical School analyzed a double-blind trial in which about 600 people received 200 mcg of selenium daily for 41/2 years. During that time, the participants had significantly fewer incidences of lung, colorectal, and prostate cancer. The same group, which continued to take the selenium, was then followed for an average of 7.7 years. In that span, type-2 diabetes developed in just under 10 percent of selenium users compared with 6.5 percent of the placebo group.

The lead researcher noted that further studies are needed, but added that most people already get adequate amounts of selenium in their food (Brazil nuts, fish, and cooked barley are particularly rich sources) so extra doses may not be worth the risk.