Photo by Karyna Panchenko on Unsplash

Vitamin D has been in the news this week. One fascinating study was published in the journal PLOS ONE. It looked at a large group of patients in the US Department of Veterans Health Affairs system who had been prescribed Vitamin D, comparing them to another group that did not receive Vitamin D. Over a two-year follow-up period, rates of suicide or suicide attempts were compared.

They found that in veterans who were Vitamin D deficient at the beginning of the study, giving Vitamin D substantially decreased the incidence of suicide attempts. But for those whose baseline Vitamin D level was over 40 ng/ml, giving Vitamin D did not affect the rate of suicide attempts.

Photo by Noah Silliman on Unsplash

This study illustrates one of the reasons why the nutritional literature can be confusing. As the discussion section of the article mentions, previous research about Vitamin D in depression found that it did not help – but those studies involved people whose blood levels were normal, or whose levels were not checked (meaning that participants in the study might or might not be deficient).

It stands to reason that vitamin supplementation is going to be effective in people who are deficient in them, and that it is hard to show benefit in people who are not deficient.