Effect of vitamin D supplementation on central adiposity in male shift workers: A randomized clinical trial

Background Low plasma levels of 25-hydroxy-vitamin D (25(OH)D) are often observed in obese individuals, but the mechanisms linking vitamin D deficiency to adiposity remain unclear. This study evaluated whether cholecalciferol supplementation influences central adiposity by assessing changes in waist circumference (WC) and waist-to-height ratio (WHtR). Methods A randomized, double-blind, placebo-controlled clinical trial was conducted with 198 shift workers from an iron ore extraction company in Minas Gerais, Brazil. Participants with 25(OH)D levels below 30 ng/mL and at least one metabolic alteration—such as metabolic syndrome, impaired fasting glucose, dyslipidemia, elevated blood pressure, or increased WC—were included. They were randomized into three groups: placebo, cholecalciferol 14,000 IU/week, and cholecalciferol 28,000 IU/week, for 4 months. Plasma 25(OH)D concentrations, WC, and WHtR were measured at baseline and post-intervention. Results After 4 months, no significant differences in WC or WHtR were observed between the vitamin D supplementation groups (14,000 IU and 28,000 IU/week) and the placebo group. However, there was a significant increase in 25(OH)D levels in the supplementation groups: +6.23 ng/mL (p25 = 0.58; p75 = 10.61) in the 14,000 IU group and + 15.25 ng/mL (p25 = 10.57; p75 = 19.68) in the 28,000 IU group, compared to a reduction of -0.50 ng/mL (p25= -1.03; p75 = 2.71) in the placebo group (p > 0.05). Conclusions In vitamin D-deficient shift workers, supplementation with cholecalciferol for 4 months significantly increased 25(OH)D levels but did not lead to reductions in WC or WHtR. These findings suggest that while vitamin D supplementation improves serum 25(OH)D concentrations, it may not directly impact central adiposity in this population.