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

Abstract

Purpose: 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 randomized, 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: In study 1, we determined 25(OH)D relationship with exercise performance in 967 military recruits. In study 2, 137 men received either placebo, simulated sunlight (1.3× standard erythemal dose in T-shirt and shorts, three times per week for 4 wk and then once per week for 8 wk) or oral vitamin D3 (1000 IU·d for 4 wk and then 400 IU·d for 8 wk). We measured serum 25(OH)D by high-pressure liquid chromatography tandem mass spectrometry and endurance, strength and power by 1.5-mile run, maximum dynamic lift and vertical jump, respectively.

Results: 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, ΔR = 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). 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 randomized-controlled trial.

FIGURE 1

Schematic of study 2 procedures, to investigate the effect of vitamin D supplementation by SSR, oral vitamin D₃ (ORAL), or placebo (SSR-P or ORAL-P) on exercise performance (1.5-mile run, maximum dynamic lift strength and explosive power), using a 4-wk restoration phase followed by an 8-wk maintenance phase. Syringe icon represents blood sample; running icon represents 1.5-mile run; weightlifting icon represents maximum dynamic lift strength; jumping icon represents explosive power; PSF, polysulphone badge; FFQ, food frequency questionnaire.

FIGURE 2

Seasonal variation in serum 25(OH)D (panel A) and percentage of participants categorized as vitamin D sufficient (serum 25(OH)D ≥ 50 nmol·L⁻¹; panel B); and 1.5-mile run time by serum 25(OH)D quartiles (panel C) in 967 healthy, young males (n = 621) and females (n = 346) residing in the UK. a, lower than summer (P < 0.05). b, lower than fall (P < 0.05). c, lower than spring (P < 0.05). §, faster than quartiles 1, 2 and 3 (P < 0.05). Panel A and C data are mean ± SD.

FIGURE 3

Serum 25(OH)D and percentage of participants categorized as vitamin D sufficient (serum 25(OH)D ≥ 50 nmol·L⁻¹) in response to 12 wk of vitamin D supplementation by SSR and oral vitamin D₃ (ORAL). Panels A and B show combined active interventions (SSR and ORAL) vs combined placebo (SSR-P and ORAL-P), panels C and D show SSR vs SSR-P, and panels E & F show ORAL vs ORAL-P. †††P < 0.001, greater than baseline. ‡‡‡P < 0.001, greater than week 5. *P < 0.05 and ***P < 0.001, greater than placebo. Data in panels A, C, and E are mean ± SD.

FIGURE 4

Serum 1,25(OH)₂D in response to 12 wk of vitamin D supplementation by SSR and oral vitamin D₃ (SSR and ORAL) vs placebo (SSR-P and ORAL-P). †P < 0.05 and ††P < 0.01, greater than baseline. ‡‡P < 0.01, greater than week 5. *P < 0.05, greater than placebo. Data are mean ± SD.