Vitamin D supplementation does not improve human skeletal muscle contractile properties in insufficient young males
Vitamin D may be a regulator of skeletal muscle function, although human trials investigating this hypothesis are limited to predominantly elderly populations. We aimed to assess the effect of oral vitamin D3 in healthy young males upon skeletal muscle function.
Participants (n = 29) received an oral dose of 10,000 IU day−1 vitamin D3 (VITD) or a visually identical placebo (PLB) for 3 months. Serum 25[OH]D and intact parathyroid hormone (iPTH) were measured at baseline and at week 4, 8 and 12. Muscle function was assessed in n = 22 participants by isokinetic dynamometry and percutaneous isometric electromyostimulation at baseline and at week 6 and 12.
Baseline mean total serum 25[OH]D was 40 ± 17 and 41 ± 20 nmol L−1 for PLB and VITD, respectively. VITD showed a significant improvement in total 25[OH]D at week 4 (150 ± 31 nmol L−1) that remained elevated throughout the trial (P < 0.005). Contrastingly, PLB showed a significant decrease in 25[OH]D at week 12 (25 ± 15 nmol L−1) compared with baseline. Despite marked increases in total serum 25[OH]D in VITD and a decrease in PLB, there were no significant changes in any of the muscle function outcome measures at week 6 or 12 for either group (P > 0.05).
Elevating total serum 25[OH]D to concentrations > 120 nmol L−1 has no effect on skeletal muscle function. We postulate that skeletal muscle function is only perturbed in conditions of severe deficiency (<12.5 nmol L−1).
KeywordsCholecalciferol 25-Hydroxyvitamin D Supplementation Isokinetic dynamometry Electromyostimulation Fatigue
Enzyme-linked chemiluminescent immunosorbent assay
Food and Drug Agency
Intact parathyroid hormone
Liquid chromatography tandem mass spectrometry
Lower limit of quantification
- nmol L−1
Nanomoles per litre
Physical activity readiness Questionnaire
- Pmol L−1
Picomoles per litre
- rad s−1
Radians per second
Recommended daily intake
- US IoM
United States Institute of Medicine
The authors would like to thank Dr. Rob Erskine and Ian Poole at LJMU for their expert technical assistance in electromyostimulation. Gratitude is also expressed by the authors to Emily Fisher, Christopher Washbourne and Isabelle Piec at UEA for the development of the LC–MS/MS assay.
Conflict of interest
The authors declare no conflicts of interest.
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