Context: There has been a resurgence of vitamin D deficiency rickets throughout the developed world, with infants and adolescents being primarily affected. Adolescence is a crucial period for muscle and bone mineral accumulation.
Objective: The aim was to determine the effect of vitamin D supplementation on the adolescent musculoskeletal system.
Design and setting: We conducted a community-based, double-blind, randomized controlled trial in a secondary school.
Participants: Postmenarchal 12- to 14-yr-old females participated in the trial. Ninety-nine were screened, 73 were included in randomized controlled trial, and 69 completed the trial. There were no adverse events.
Intervention: Four doses of 150,000 IU vitamin D(2) (ergocalciferol) were given over 1 yr.
Main outcome measures: Dual-energy x-ray absorptiometry, peripheral quantitative computed tomography, and jumping mechanography were used.
Results: At follow-up, 25-hydroxyvitamin D [25(OH)D] status was 56.0 ± 8.9 nmol/liter in the intervention group and 15.8 ± 6.6 nmol/liter in controls. There were no effects of supplementation on bone; however, for muscle function, efficiency of movement improved in the vitamin D-treated group. There was an interaction between baseline 25(OH)D concentration and response to vitamin D supplementation for muscle jump velocity.
Conclusions: Despite improvements in 25(OH)D status, treatment with vitamin D(2) was not shown to increase mineral accretion, bone geometry or strength, muscle force, or power. There were greater increases in jump velocity in girls with the lowest baseline 25(OH)D concentrations. Lack of effect of intervention after the period of peak mineral and muscle mass accretion suggests that earlier action is required.