Winter Cholecalciferol Supplementation at 51°N Has No Effect on Markers of Cardiometabolic Risk in Healthy Adolescents Aged 14-18 Years

Background: Epidemiological studies have supported inverse associations between low serum 25-hydroxyvitamin D [25(OH)D] and cardiometabolic risk markers, but few randomized trials have investigated the effect of vitamin D supplementation on these markers in adolescents. Objective: The objective of this study was to investigate the effect of winter-time cholecalciferol (vitamin D3) supplementation on cardiometabolic risk markers in white, healthy 14-18 year-old adolescents in the UK (51°N) as part of the ODIN Project. Methods: In a dose-response trial, 110 adolescents (15.9±1.4 years; 43% male; 81% normal weight) were randomly assigned to receive 0, 10 or 20 μg/day vitamin D3 for 20 weeks (October-March). Cardiometabolic risk markers including BMI-for-age z-score (BMIz), waist circumference, systolic and diastolic blood pressure, fasting plasma triglycerides, cholesterol (total, HDL, LDL and total:HDL) and glucose were measured at baseline and endpoint as secondary outcomes, together with serum 25(OH)D. Intervention effects were evaluated in linear regression models as between-group differences at endpoint, adjusted for the baseline value of the outcome variable and additionally for age, sex, Tanner stage, BMIz and baseline serum 25(OH)D. Results: Mean±SD baseline serum 25(OH)D was 49.1±12.3 nmol/L and differed between groups at endpoint with concentrations of 30.7±8.6, 56.6±12.4 and 63.9±10.6 nmol/L in the 0, 10 and 20 μg/day groups respectively (P≤0.001). Vitamin D3 supplementation had no effect on any of the cardiometabolic risk markers (all P>0.05), except for lower HDL (-0.12 mmol/L, 95% CI -0.21, 0.04, P=0.003) and total cholesterol (-0.21 mmol/L, 95% CI -0.42, 0.00, P=0.05) in the 20 compared to the 10 μg/day group, which disappeared in the fully adjusted analysis (P=0.27 and P=0.30 respectively). Conclusions: Supplementation with vitamin D3 at 10 and 20 μg/25 day, which increased serum 25(OH)D concentrations during the winter-time, had no effect on markers of cardiometabolic risk in healthy 14-18 year-old adolescents. This trial was registered at clinicaltrials.gov as NCT02150122.