Effect of vitamin D supplementation on depressive symptoms and psychological wellbeing in healthy adult women: a double-blind randomised controlled clinical trial

Double-blind randomized placebo-controlled trial in healthy premenopausal women aged 18-40 years in Dunedin, New Zealand, conducted over winter. In the vitamin D3 group, 76 participants were randomized.

Oral vitamin D3 (cholecalciferol) 50,000 IU (1.25 mg) was given once monthly for 6 months as gelatine capsules, compared with identical placebo capsules. Compliance was checked by returned tablet count.

Vitamin D3 supplementation did not improve mood-related outcomes over winter in this population. At follow-up, there were no significant between-group effects for depressive symptoms (P = 0.339), anxiety (P = 0.862), flourishing (P = 0.453), positive mood (P = 0.518), or negative mood (P = 0.538). The authors concluded that monthly vitamin D3 does not support use for depressive symptoms or psychological wellbeing in healthy adult women.

The trial was relatively small and limited to healthy young women from a single center in New Zealand, which restricts generalizability. Follow-up was only 6 months and covered one winter season, and baseline flourishing differed between groups. No adverse events were reported, but outcome data were based on self-reported mood measures and the study was not powered for subtle psychological effects.