Vitamin D Supplementation Does Not Impact Insulin Resistance in Black and White Children.

This was a multi-site, randomized, intent-to-treat dose-response trial in apparently healthy Black and White children in early puberty, ages 9 to 13 years. Participants were recruited in the United States at the University of Georgia, Purdue University, and Indiana University, with wintertime testing.

Oral vitamin D3 tablets were given once daily for 12 weeks at dose levels of 400 IU/day, 1000 IU/day, 2000 IU/day, or 4000 IU/day. The trial used a dose-response design with equal randomization across five daily dose groups; the active supplement was vitamin D3.

Vitamin D3 supplementation did not improve fasting glucose, fasting insulin, or HOMA-IR over 12 weeks. Serum 25(OH)D increased in a dose-dependent manner, but vitamin D dose had no impact on insulin resistance outcomes. Across the cohort, 25(OH)D was inversely associated with insulin (r = -0.140, P = .017) and HOMA-IR (r = -0.146, P = .012) at baseline, yet this did not translate into a causal benefit from supplementation. Glucose, insulin, and HOMA-IR increased over time overall (F > 5.79, P < .003), but not in a way that favored vitamin D treatment.

The intervention lasted only 12 weeks and enrolled generally healthy children with relatively sufficient baseline vitamin D status, which may have limited detectable benefit. Outcome and subgroup data were reported largely at the cohort level rather than by active arm, and no specific adverse-event results were provided. The sample was restricted to early pubertal Black and White children in wintertime, limiting generalizability.