This week another dietary supplement moves from the “not proven to have any benefits” column to the “potentially harmful” column.  A study in the Annals of Internal Medicine which was reported in this CNN article is the largest study yet to look at the effects of selenium on the development of diabetes.

This story actually starts over a decade ago with a study designed to test if selenium prevents cancer.  The authors randomized 1,312 patients of a dermatology clinic with a history of skin cancer to receive either a selenium supplement or placebo.  The patients were then followed to see if selenium led to a lower risk of developing new skin cancers.  It didn’t.  (The results were published in this 1996 paper in the Journal of the AMA.)

In this week’s study the data from the first study was re-analyzed looking at the development of diabetes.  Patients who had a diagnosis of diabetes at the start of the study were excluded, and numbers of patients in each group who developed diabetes during the initial trial were counted.  Surprisingly, the patients in the selenium group developed diabetes more frequently than the placebo group at a rate that suggested that for every 25 people who take selenium rather than placebo for 10 years one additional case of diabetes would result.

So selenium doesn’t prevent skin cancer and may actually increase the risk of developing diabetes.  Of course we already have lots of ways to increase the risk of diabetes.  My favorite one is cheesecake.

Thanks to Linda T. for pointing me to this story.