Correcting vitamin D insufficiency improves insulin sensitivity in obese adolescents: a randomized controlled trial.

Randomized controlled trial in obese adolescents with baseline vitamin D deficiency or insufficiency. The vitamin D arm included 21 participants and the placebo arm included 23 participants; all were ages 9 to 19 years with BMI at least the 85th percentile.

Vitamin D3 (cholecalciferol) 4000 IU/day was given orally as two indistinguishable 2000 IU pills daily for 6 months. The active intervention was compared with placebo.

Vitamin D3 supplementation safely corrected insufficiency in most participants and improved markers of insulin sensitivity compared with placebo. By 6 months, 93% of the vitamin D group had sufficient 25(OH)D, and between-group changes favored vitamin D for fasting insulin (P = 0.026), HOMA-IR (P = 0.033), QUICKI (P = 0.016), and leptin-to-adiponectin ratio (P = 0.045). Fasting glucose did not show a significant between-group change (P = 0.085), and CRP, IL-6, and TNF-alpha were largely unchanged. The authors concluded that correcting vitamin D insufficiency may be a useful adjunct to obesity treatment in obese adolescents.

The trial was small, with only 21 participants in the vitamin D arm and 23 in placebo, which limits precision. Follow-up was limited to 6 months, and inflammatory markers did not improve. Adverse events were not reported, and the findings apply specifically to obese adolescents with low vitamin D status.