This week in The British Journal of Psychiatry, researchers in Norway have published results from their randomised 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:
- The Beck Depression Inventory (BDI) – a self-completed 21-item questionnaire
- The Hospital Anxiety and Depression Scale (HADS) – a multiple-choice 14 question survey on depression and anxiety
- The Seasonal Pattern Assessment Scale (GSS) – a 6 item questionnaire used to assess symptoms involved in seasonal affective disorder
- Montgomery-Asperg Depression Rating Scale (MADRS) – a 10 question survey assessing depressive symptoms
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:
- In a study by Sanders et al, a one-time dose of 500,000 IU had no effect on mental well-being in 2,258 community-dwelling elderly women.
- On the other hand, a Vieth et al study found that vitamin D at 4,000 IU/day performed better than 600 IU/day for general well being in a small pool of 130 participants.
- Furthermore, Lansdowne and Provost reported a significant improvement in mood in 44 healthy subjects who were given either 400 IU or 800 IU of vitamin D in conjunction with vitamin A compared to just vitamin A alone.
- Lastly, a Jorde et al study administered 20,000 IU or 40,000 IU of vitamin D/week or placebo in 441 overweight women for a year and saw an improvement in the same BDI questionnaire used in this study.
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.
Ksaergaard 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. [PubMed abstract]