Obesity often coexists with poor vitamin D status. There is emerging evidence that improving vitamin D status could
lower prevalence of many chronic diseases. We questioned whether vitamin D influenced body fat mass.
A literature search from 1995 to date was conducted using prominent databases. Selection criteria included human,
randomized controlled trials (RCTs) that were designed to test the supplementation of vitamin D on body weight and
Eleven RCTs (4 primary and 7 secondary) that supplemented vitamin D met our criteria. Nine studies were of good
quality with a Jadad et al. score ≥3. Three favoured an effect of vitamin D on body fatness, while six showed no
difference between treatments. Better vitamin status before or during an RCT predicted greater weight and/or fat loss in a
Current evidence from RCTs of good quality did not unequivocally support the contention that vitamin D accelerated
weight or fat loss in obesity. Direct mechanistic pathways for obesity prevention remain untested in humans, though an
indirect effect through an improvement in calcium metabolism, was plausible. Outcomes from trials recently completed or
in progress will strength the evidence base in this important area.