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 μg (1000 IU) vitamin D3, 10 μg (400 IU) vitamin D3, 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 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.

CONCLUSIONS: 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.