RESUMEN
BACKGROUND: The role of vitamin D on muscle health is debated. METHODS: An individual participant metanalysis of 4 randomized placebo-controlled trials, investigating short-term (3-9months) effects of vitamin D3 in moderate (2800 IU) to high (7000 IU) daily oral doses on muscle health and quality of life (QoL). Inclusion criteria were either obesity (nâ =â 52), newly diagnosed primary hyperparathyroidism (nâ =â 41), Graves' disease (nâ =â 86), or secondary hyperparathyroidism (nâ =â 81). RESULTS: Overall (nâ =â 260) as well as in a subgroup analysis including only vitamin D insufficient [25(OH)Dâ <â 50 nmol/L] individuals (nâ =â 176), vitamin D supplementation did not affect measures of muscle health (isometric muscle strength, Timed Up and Go test, chair rising test, body composition, and balance) or QoL. However, a beneficial effect was present on QoL (physical component score) in vitamin D deficient [25(OH)Dâ <â 25 nmol/L] individuals (nâ =â 34). Overall, relative changes in 25(OH)D inversely affected maximum muscle strength in a dose-response manner. Stratified into body mass index > 30 kg/m2, vitamin D supplementation had divergent effects on isometric muscle strength, with beneficial effects in obese individuals (nâ =â 93) at knee flexion 90° (Pâ =â 0.04), and adverse effects in nonobese individuals (nâ =â 167) at handgrip (Pâ =â 0.02), knee extension 60° (Pâ =â 0.03) and knee flexion 60° (Pâ <â 0.01). CONCLUSION: Overall, short-term treatment with moderate to high daily doses of vitamin D did not affect muscle health or QoL. A potential beneficial effect was present on muscle strength in severely obese individuals and on QoL in vitamin D deficient individuals. Subgroup analyses, however, suggested negative effects of large relative increases in p-25(OH)D.