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

Background: Adolescents are a population group at high risk of low vitamin D status, yet the evidence base for establishing dietary vitamin D requirements remains weak. Objective: The aim was to establish the distribution of vitamin D intakes required to maintain serum 25-hydroxyvitamin D 125(OH)D] concentrations above proposed cutoffs (25, 30, 40, and 50 nmol/L) during winter in white males and females (14-18 y of age) in the United Kingdom (51 degrees N). Design: In a dose-response trial, 110 adolescents (aged 15.9 +/- 1.4 y; 43% males) were randomly assigned to receive 0, 10, or 20 mu g Vitamin D-3 supplements/d for 20 wk during winter. A nonlinear regression model was fit to total vitamin D intake and postintervention serum 25(OH)D concentrations, and regression-predicted values estimated the vitamin D intakes required to maintain serum 25(OH)D concentrations above specific cutoffs. Results: Mean +/- SD serum 25(OH)D concentrations increased from 49.2 +/- 12.0 to 56.6 +/- 12.4 nmol/L and from 51.7 +/- 13.4 to 63.9 +/- 10.6 nmol/L in the 10- and 20-mu g/d groups, respectively, and decreased in the placebo group from 46.8 +/- 11.4 to 30.7 +/- 8.6 nmol/L (all P <= 0.001). Vitamin D intakes required to maintain 25(OH)D concentrations >25 and >30 nmol/L in 97.5% of adolescents were estimated to be 10.1 and 13.1 mu g/d, respectively, and 6.6 mu g/d to maintain 50% of adolescents at concentrations >40 nmol/L. Because the response of 25(OH)D reached a plateau at 46 nmol/L, there is uncertainty in estimating the vitamin D intake required to maintain 25(OH)D concentrations >50 nmol/L in 97.5% of adolescents, but it exceeded 30 mu g/d. Conclusion: Vitamin D intakes between 10 and similar to 30 mu g/d are required by white adolescents during winter to maintain serum 25(OH)D concentrations >25-50 nmol/L, depending on the serum 25(OH)D threshold chosen.