Effects of different vitamin D supplementation strategies in reversing metabolic syndrome and its component risk factors in adolescents

There is little evidence on the efficacy of various vitamin D supplementation strategies in reversing metabolic syndrome (MetS) in adolescents. The present study aims to fill this gap. A total of 535 (243/292) out of 650 apparently healthy Saudi adolescents were randomly selected from the Vitamin D School Project database which has baseline and post-intervention information of more than 1000 Saudi adolescents 12-18 years old attending 34 schools in Riyadh, Saudi Arabia from Nov 2014-May 2015. Allocation of intervention was done in 3 groups using cluster randomization: vitamin D tablet, 1000IU/day (N = 180; 69 boys, 111 girls); vitamin D fortified milk consumption, 200 ml/day, 40IU/100 ml (N = 189; 93 boys, 96 girls) and control (educational awareness) (N = 166; 81 boys, 85 girls). All groups were given educational awareness on how to increase vitamin D levels. All groups were matched for BMI and analysis adjusted for age. Post-intervention and using intent-to-treat approach, within-group analysis revealed a statistically significant increase in 25(OH)D levels in all groups, and a clinically significant increase in favor of the tablet group (between-group) [10.7 nmol/1 (34.7%) versus 6.3 nmol/l (19.8%) in milk and 2.1 nmol/l (7.0%) in control; p < 0.001], adjusted for age and BMI-matched. Between group analysis also revealed a clinically significant decrease in triglycerides (p = 0.05), glucose (p < 0.001) and systolic blood pressure (p = 0.005) as well as a clinically significant increase in HDL-cholesterol (p = 0.004) over time, all in favor of the tablet group. Within-group comparison showed a significant decrease in the incidence of MetS in the tablet group (9.4% versus 4.4%; p < 0.05) only. In conclusion, oral vitamin D supplementation is superior to vitamin D fortified milk in improving vitamin D status. Reduction in the incidence of MetS in the Arab adolescent population secondary to vitamin D correction may be dose-dependent.