title: Does vitamin D improve muscle strength in adults? A randomized, double-blind, placebo-controlled trial among ethnic minorities in Norway.
abstract: BACKGROUND
  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.
  
  
  METHODS
  We conducted a randomized, double-blind, placebo-controlled trial.
  
  
  METHODS
  The setting was immigrants' activity centers.
  
  
  METHODS
  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.
  
  
  METHODS
  Sixteen weeks of daily supplementation with 25 μg (1000 IU) vitamin D3, 10 μg (400 IU) vitamin D3, or placebo.
  
  
  METHODS
  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.
authors.affiliation: Department of General Practice (K.V.K., P.L., M.B.), Institute of Health and Society, University of Oslo, Oslo N-0318, Norway; Department of Community Medicine (A.A.M., H.E.M.), Institute of Health and Society, University of Oslo, Oslo N-0318, Norway; Division of Epidemiology (L.C.S., H.E.M.), Norwegian Institute of Public Health, Oslo N-0403, Norway; and Norwegian School of Sport Sciences (T.R.), Oslo N-0806, Norway.
authors.forename: Kirsten V
authors.initials: KV
authors.lastname: Knutsen
authors.forename: Ahmed A
authors.initials: AA
authors.lastname: Madar
authors.forename: Per
authors.initials: P
authors.lastname: Lagerløv
authors.forename: Mette
authors.initials: M
authors.lastname: Brekke
authors.forename: Truls
authors.initials: T
authors.lastname: Raastad
authors.forename: Lars C
authors.initials: LC
authors.lastname: Stene
authors.forename: Haakon E
authors.initials: HE
authors.lastname: Meyer
mesh_terms: D000293:Adolescent; D000328:Adult; D019587:Dietary Supplements; D004311:Double-Blind Method; D005006:Ethnicity; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D008913:Minority Groups; D053580:Muscle Strength / Q000187:drug effects*; D009664:Norway / Q000208:ethnology; D010919:Placebos; D014807:Vitamin D / Q000008:administration & dosage*; D055815:Young Adult
chemical_list: D010919:Placebos; D014807:Vitamin D