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

The effect of vitamin D on muscle strength in adults is not established.Our objective was to test whether vitamin D supplementation increases muscle strength and power compared with placebo.We conducted a randomized, double-blind, placebo-controlled trial.The setting was immigrants' activity centers.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.Sixteen weeks of daily supplementation with 25 μg (1000 IU) vitamin D3, 10 μg (400 IU) vitamin D3, or placebo.Difference in jump height between pre- and postintervention. Secondary outcomes were differences in handgrip strength and chair-rising test.Percentage change in jump height did not differ between those receiving vitamin D (25 or 10 μg vitamin D3) 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 μg 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 D3 concentration increased from 27 to 52 nmol/L and from 27 to 43 nmol/L in the 25 and 10 μg supplementation groups, respectively, whereas serum 25-hydroxyvitamin D3 did not change in the placebo group.Daily supplementation with 25 or 10 μg vitamin D3 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.