Estimation of the dietary requirement for vitamin D in adolescents aged 14-18 y: a dose-response, double-blind, randomized placebo-controlled trial.

Double-blind, randomized, placebo-controlled dose-response trial conducted during winter in healthy white adolescents aged 14 to 18 years in the United Kingdom. Active intervention groups included 35 participants in the 10 mg/day arm and 36 participants in the 20 mg/day arm.

Oral vitamin D3 tablets were given daily for 20 weeks at two active doses: 10 mg/day and 20 mg/day. The tablets contained 10.9 mg and 22.4 mg of vitamin D3 per tablet, respectively; placebo tablets contained <0.2 mg.

Vitamin D3 increased serum 25(OH)D concentrations in both active arms, while calcium and PTH were essentially unchanged. In the 10 mg/day group, mean 25(OH)D rose from 49.2 6 12.0 to 56.6 6 12.4 nmol/L, with a total change of 6.7 6 9.9 nmol/L; in the 20 mg/day group, it rose from 51.7 6 13.4 to 63.9 6 10.6 nmol/L, with a total change of 12.1 6 10.6 nmol/L. Between-group differences at the end of the trial were significant, P < 0.001. The trial supports vitamin D supplementation as effective for raising winter 25(OH)D in adolescents, with higher intakes producing larger increases.

Active-arm sample sizes were modest, and the study population was limited to healthy white UK adolescents studied in winter, which narrows generalizability. The highest intake threshold was difficult to estimate precisely because of a plateau in the 25(OH)D response, and detailed placebo-arm outcome data were not included in the provided extraction.