What is the Influence of Vitamin D Supplementation by Sunlight on Exercise Performance in Military Recruits?

Research Paper Title

Influence of Vitamin D Supplementation by Sunlight or Oral D3 on Exercise Performance.

Background

To determine the relationship between vitamin D status and exercise performance in a large, prospective cohort study of young men and women across seasons (Study-1). Then, in a randomised, placebo-controlled trial, to investigate the effects on exercise performance of achieving vitamin D sufficiency (serum 25(OH)D ≥ 50 nmol·L) by a unique comparison of safe, simulated-sunlight and oral vitamin D3 supplementation in wintertime (Study-2).

Methods

  1. In Study-1, the researchers determined 25(OH)D relationship with exercise performance in 967 military recruits.
  2. In Study-2, 137 men received either:
    1. Placebo, simulated-sunlight (1.3x standard erythemal dose in T-shirt and shorts, three-times-per-week for 4-weeks and then once-per-week for 8-weeks); or
    2. Oral vitamin D3 (1,000 IU day for 4-weeks and then 400 IU day for 8-weeks).

The researchers measured serum 25(OH)D by LC-MS/MS and endurance, strength and power by 1.5-mile run, maximum-dynamic-lift and vertical jump, respectively.

Results

  1. In Study-1, only 9% of men and 36% of women were vitamin D sufficient during wintertime. After controlling for body composition, smoking and season, 25(OH)D was positively associated with endurance performance (P ≤ 0.01, [INCREMENT]R = 0.03-0.06, small f effect sizes): 1.5-mile run time was ~half-a-second faster for every 1 nmol·L increase in 25(OH)D. No significant effects on strength or power emerged (P > 0.05).
  2. In Study-2, safe simulated-sunlight and oral vitamin D3 supplementation were similarly effective in achieving vitamin D sufficiency in almost all (97%); however, this did not improve exercise performance (P > 0.05).

Conclusions

Vitamin D status was associated with endurance performance but not strength or power in a prospective cohort study. Achieving vitamin D sufficiency via safe, simulated summer sunlight or oral vitamin D3 supplementation did not improve exercise performance in a randomised-controlled trial.

Reference

Carswell, A.T., Oliver, S.J., Wentz, L.M., Kashi, D.S., Roberts, R., Tang, J.C.Y., Izard, R.M., Jackson, S., Allan, D., Rhodes, L.E., Fraser, W.D.3, Greeves, J.P. & Walsh, N.P. (2018) Influence of Vitamin D Supplementation by Sunlight or Oral D3 on Exercise Performance. Medicine & Science in Sport & Exercise. doi: 10.1249/MSS.0000000000001721. [Epub ahead of print].

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