Does Vitamin D Improve Muscle Strength in Adults? A Randomized, Double-blind, Placebo-controlled Trial Among Ethnic Minorities in Norway

Context: The effect of vitamin D on muscle strength in adults is not established. Objective: Our objective was to test whether vitamin D supplementation increases muscle strength and power compared with placebo. Design: We conducted a randomized, double-blind, placebo-controlled trial. Setting: The setting was immigrants' activity centers. Participants: Two hundred fifty-one healthy adult males and females aged 18-50 years with non-Western immigrant background performed the baseline test and 86% returned to the follow-up test. Interventions: Sixteen weeks of daily supplementation with 25 mu g (1000 IU) vitamin D-3, 10 mu g (400 IU) vitamin D-3, or placebo. Main Outcome Measures: Difference in jump height between pre- and postintervention. Secondary outcomes were differences in handgrip strength and chair-rising test. Results: Percentage change in jump height did not differ between those receiving vitamin D (25 or 10 mu g vitamin D-3) and those receiving placebo (mean difference - 1.4%, 95% confidence interval: -4.9% to 2.2%, P = .44). No significant effect was detected in the subgroup randomized to 25 mu g vitamin D or in other preplanned subgroup analyses nor were there any significant differences in handgrip strength or the chair-rising test. Mean serum 25-hydroxyvitamin D-3 concentration increased from 27 to 52 nmol/L and from 27 to 43 nmol/L in the 25 and 10 mu g supplementation groups, respectively, whereas serum 25-hydroxyvitamin D-3 did not change in the placebo group. Conclusions: Daily supplementation with 25 or 10 mu g vitamin D-3 for 16 weeks did not improve muscle strength or power measured by the jump test, handgrip test, or chair-rising test in this population with low baseline vitamin D status.