Effects of vitamin D supplementation and seasonality on circulating cytokines in adolescents: analysis of data from a feasibility trial in Mongolia.

Vitamin D deficiency is prevalent in human populations and has been linked to immune dysfunction. Here we explored the effects of cholecalciferol supplementation on circulating cytokines in severely vitamin D deficient (blood 25(OH)D3 << 30 nmol/L) adolescents aged 12-15 from Mongolia. The study included 28 children receiving 800 IU daily cholecalciferol for 6 months spanning winter and spring, and 30 children receiving placebo during the same period. The levels of 25(OH)D3 were assessed at baseline, three and six months. Twenty-one cytokines were measured in serum at baseline and at six months. The median blood 25(OH)D3 concentration at baseline was 13.7 nmol/L (IQR=10.0-21.7). Supplementation tripled blood 25(OH)D3 levels (p<0.001) and reversed the direction of change for most cytokines (16/21, 86%). Supplementation was associated with elevated interleukin (IL)-6 (p=0.043). The placebo group had reduced MIP-1 (p=0.007) and IL-8 (p=0.034) at six months. These findings suggest that cholecalciferol supplementation and seasonality have a measurable impact on circulating cytokines in adolescents, identifying chemokines as potentially important biomarkers of vitamin D status in this population. ClinicalTrial.org ID: NCT01244204