A parallel group double-blind RCT of vitamin D3 assessing physical function: is the biochemical response to treatment affected by overweight and obesity?

A. D. Wood, K. R. Secombes, F. Thies, L. S. Aucott, A. J. Black, D. M. Reid, A. Mavroeidi, W. G. Simpson, W. D. Fraser, H. M. Macdonald

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Vitamin D may affect skeletal muscle function. In a double-blind, randomised, placebo-controlled trial, we found that vitamin D3 supplementation (400 or 1,000 I.U. vs. placebo daily for 1 year with bimonthly study visits) does not improve grip strength or reduce falls. Introduction: This study aimed to test the supplementation effects of vitamin D3 on physical function and examine associations between overweight/obesity and the biochemical response to treatment. Methods: In a parallel group double-blind RCT, healthy postmenopausal women from North East Scotland (latitude - 57 N) aged 60-70 years (body mass index (BMI), 18-45 kg/m2) were assigned (computer randomisation) to daily vitamin D3 (400 I.U. (n = 102)/1,000 I.U. (n = 101)) or matching placebo (n = 102) (97, 96 and 100 participants analysed for outcomes, respectively) from identical coded containers for 1 year. Grip strength (primary outcome), falls, diet, physical activity and ultraviolet B radiation exposure were measured bimonthly, as were serum 25(OH)D, adjusted calcium (ACa) and phosphate. Fat/lean mass (dual energy X-ray absorptiometry), anthropometry, 1,25-dihydroxyvitamin D and parathyroid hormone were measured at baseline and 12 months. Participants and researchers were blinded throughout intervention and analysis. Results: Treatment had no effect on grip strength (mean change (SD)/year = -0.5 (2.5), -0.9 (2.7) and -0.4 (3.3) kg force for 400/1,000 I.U. vitamin D3 and placebo groups, respectively (P =.10, ANOVA)) or falls (P =.65, chi-squared test). Biochemical responses were similar across BMI categories (<25.25-29.99, ≥30 kg/m 2) with the exception of a small change at 12-months in serum ACa in overweight compared to non-overweight participants (P =.01, ANOVA; 1,000 I.U. group). In the placebo group, 25(OH)D peak concentration change (winter to summer) was negatively associated with weight (r = -.268), BMI (r = -.198), total (r = -.278) and trunk fat mass (r = -.251), with total and trunk fat mass predictive of winter to summer 25(OH)D change (P =.01/.004 respectively, linear regression). Conclusion: We found no evidence of an improvement in physical function following vitamin D3 supplementation for 1 year.

Original languageEnglish
Pages (from-to)305-315
Number of pages11
JournalOsteoporosis International
Issue number1
Early online date28 Aug 2013
Publication statusPublished - 31 Jan 2014


  • adiposity
  • body mass index
  • falls
  • grip strength
  • RCT
  • vitamin D
  • physical function

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