Vitamin D Supplementation and Muscle Strength and Bone Health Outcomes: A Phase 3 Randomized Trial in 8,851 Schoolchildren

OBJECTIVES: To determine the effects of vitamin D supplementation on muscle strength and bone health in vitamin D-deficient schoolchildren. METHODS: We performed a phase 3 randomized placebo-controlled clinical trial in Ulaanbaatar, Mongolia, to determine whether weekly oral supplementation with 14,000 IU vitamin D(3), administered for 3 years in 8,851 schoolchildren aged 6 to 13 years. We evaluated effects of the intervention on bone mineral density (BMD) (n = 1,465), physical fitness (n = 615), long jump (n = 8,850), grip strength (n = 8,850) and incidence of fracture (n = 8,850). Analyses were conducted for all efficacy outcomes to determine whether the effect of the intervention varied according to baseline 25-hydroxyvitamin D levels and calcium intake. RESULTS: Of the 8,851 randomized participants, 95.6% had vitamin D deficiency (25[OH]D < 20 ng/mL) at baseline, and 91.7% completed the study. Mean end-study 25(OH)D levels were 29.8 vs. 9.7 ng/mL in children randomized to intervention vs. placebo (p < 0.001). Vitamin D supplementation did not reduce the incident fracture (P = 0.65), mean radial BMD z-score (P = 0.14), mean maximal oxygen consumption during a 20 meter shuttle run (VO2max, P = 0.22), mean grip strength (p = 0.77) and mean long jump distance (p = 0.23). Effects of the intervention did not differ according to baseline 25-hydroxyvitamin D levels (<10 ng/mL vs. ≥10 ng/mL) for any efficacy outcome studied in subset population. CONCLUSIONS: A weekly oral dose of 14,000 IU (3.5 mg) vitamin D3, administered for 3 years, was safe and effective in elevating 25-hydroxyvitamin D levels into the high physiological range in vitamin D-deficient schoolchildren, but it did not affect any efficacy outcome in muscle strength and bone health. FUNDING SOURCES: National Institutes of Health, 1R01HL122624-01.