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Although observational studies have linked symptoms of depression to low vitamin D levels, few randomized, controlled trials have tested whether vitamin D supplementation can treat or prevent depression. These studies had modest and, often, selective samples and yielded conflicting results. Researchers have now analyzed data from the Women's Health Initiative Calcium and Vitamin D Trial in 36,282 women aged 50 to 80 who were randomized to 400 IU vitamin D (with 1000 mg calcium) or to placebo. Depression symptoms and antidepressant use (as proxy for depression) were measured at randomization and 2 years later (symptoms measured at follow-up in only 2263 women).
The two groups had low baseline levels of antidepressant use (7%), threshold depre…