Vitamin D may have a significant positive effect on symptoms of depression*

Prior studies of vitamin D and depression had inconsistent findings because they were flawed, according to researchers who conducted this new review. Many of the earlier studies failed to measure vitamin D levels in participants, or used too small or too large a dose. In an attempt to get more reliable results, researchers separated the flawed studies from the well-constructed studies and re-analyzed them. Doctors found that vitamin D, when measured properly in participants and given in doses of 1,200 IU per day, had a significant positive effect on symptoms of depression.

When reviewing only the flawed studies, doctors found the opposite effect. When researchers combined both the flawed and well-constructed studies, the large size of some of the flawed studies overpowered the findings from the well-constructed studies. For example, one flawed study used a 200 IU dose of vitamin D on a population of 160,000 women, and found weak results for mood; enough to obscure the real benefits of vitamin D in reducing symptoms of depression.

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