This week in The British Journal of Psychiatry, researchers in Norway have published results from their randomized controlled trial studying the effects of vitamin D on depressive symptoms in otherwise healthy adults.
The study, directed by Dr Marie Kjaergaard and a team of doctors out of the University Tromsø in Norway, found that vitamin D did not beat placebo in improving depressive symptoms in a population of people with low vitamin D levels.
The researchers studied the effects of 40,000 IU of vitamin D₃ per week for 6 months. They randomized 231 participants to either a placebo group or the vitamin D group. The participants had baseline vitamin D levels of 19 ng/ml. They also measured at baseline and 6 months:
After 6 months, the vitamin D group’s vitamin D levels rose from 19 ng/ml to a mean level of 59 ng/ml. The placebo group’s levels rose three points to 21 ng/ml. Generally, both the placebo and vitamin D groups’ depression scores improved. However, there was no significant difference between placebo and vitamin D in improving these scores.
In a post hoc analysis, the researchers found a statistically significant improvement in HADS score in the vitamin D group over placebo if the patients started with high scores of BDI, HADS and MADRS. On the other hand, placebo performed better than vitamin D in BDI and MADRS scores if the patients started with low BDI, HADS and MADRS scores. Given this discrepancy, the researchers could not ascertain any difference between vitamin D and placebo.
In further post hoc analysis, there was no difference in the effect of vitamin D supplementation in people that were severely deficient in vitamin D versus moderately deficient in vitamin D. Interestingly, 6 patients dropped out of the placebo group during the study due to “adverse events,” while only 1 patient in the vitamin D group dropped out.
Past studies have found mixed results. These results include:
The authors note that the biggest limitation in their study was study length at 6 months in a disorder that may take several years to develop. They call for more research to definitively answer the question if vitamin D plays a role in depression. We also need a better understanding of how vitamin D affects the brain.
Kjaergaard M et al. Effect of vitamin D supplement on depression scores in people with low levels of serum 25-hydroxyvitamin D: nested case-control study and randomised clinical trial. The British Journal of Psychiatry, 2012.
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