Recent evidence suggests that vitamin D deficiency may contribute to increased risk of depression. However, previous studies are limited by variability in participant characteristics including vitamin D deficiency status and presence of existing diseases, use of low doses of vitamin D supplementation for short durations, and use of co-interventions or psychotropic drugs. We examined whether 25-hydroxyvitamin D (25(OH)D) concentrations were associated with symptoms of depression, as well as whether vitamin D supplementation reduced symptoms of depression in overweight or obese and vitamin D-deficient, but otherwise healthy adults.Cross-sectional analyses were performed on baseline data from 63 (39 M/24F) overweight or obese (body mass index (BMI) >= 25 kg/m(2)) and vitamin D-deficient (25(OH)D <= 50 nmol/l) adults (mean age = 31.3 +/- 8.5), without clinical depression. Participants were randomized to either a bolus oral dose of 100,000 IU followed by 4000 IU daily of cholecalciferol, or matching placebo for 16 weeks. Interventional analyses were performed on data from 48 participants (30 M/18F) who completed the trial. We measured serum 25(OH)D concentrations; anthropometry: BMI, waist-to-hip ratio (WHR), % body fat (dual X-ray absorptiometry); and depressive symptoms using the Beck Depression Inventory (BDI) before and after intervention. Data on dietary vitamin D intake (3-day food record), physical activity (international physical activity questionnaire), and sun exposure habits were collected using questionnaires.At baseline, mean 25(OH)D concentration was 32.9 +/- 11.3 nmol/l and total BDI score was 6.6 +/- 6.3 (range = 0-33). There were no associations between 25(OH)D concentrations and total BDI scores or BDI subscales (all p > 0.1). After the 16-week intervention, 25(OH)D concentrations increased in the vitamin D group compared to placebo (56.0 +/- 20.8 versus 2.7 +/- 13.9 nmol/L, respectively; p < 0.0001). Change in total BDI scores did not differ between vitamin D and placebo groups ( 2.0 +/- 4.5 versus 1.5 +/- 2.9, respectively; p = 0.7). There were no differences in BDI subscales between groups (both p > 0.1). Results remained non-significant after adjusting for multiple covariates including sun exposure, physical activity, and dietary vitamin D intake (all p > 0.1).Our findings suggest that vitamin D deficiency may not be related to increased risk of depression in individuals without clinically significant depression and that the use of vitamin D supplementation may not be warranted for reducing depressive symptoms in this population. Further large-scale studies are needed to establish whether vitamin D supplementation may be beneficial for improving depressive symptoms in other population groups, including in those with existing depressive or psychiatric disorders.