Abstract
The purpose of this review is to examine vitamin D in the context of sport nutrition and its potential role in optimizing athletic performance. Vitamin D receptors (VDR) and vitamin D response elements (VDREs) are located in almost every tissue within the human body including skeletal muscle. The hormonally-active form of vitamin D, 1,25-dihydroxyvitamin D, has been shown to play critical roles in the human body and regulates over 900 gene variants. Based on the literature presented, it is plausible that vitamin D levels above the normal reference range (up to 100 nmol/L) might increase skeletal muscle function, decrease recovery time from training, increase both force and power production, and increase testosterone production, each of which could potentiate athletic performance. Therefore, maintaining higher levels of vitamin D could prove beneficial for athletic performance. Despite this situation, large portions of athletic populations are vitamin D deficient. Currently, the research is inconclusive with regards to the optimal intake of vitamin D, the specific forms of vitamin D one should ingest, and the distinct nutrient-nutrient interactions of vitamin D with vitamin K that affect arterial calcification and hypervitaminosis. Furthermore, it is possible that dosages exceeding the recommendations for vitamin D (i.e. dosages up to 4000-5000 IU/day), in combination with 50 to 1000 mcg/day of vitamin K1 and K2 could aid athletic performance. This review will investigate these topics, and specifically their relevance to athletic performance.
Highlights
Vitamin D, a fat-soluble vitamin, was first discovered in cod liver oil [1] and has since been identified as an essential vitamin, acting as a precursor steroid to a host of metabolic and biological processes
It has been shown that it takes roughly 2000 to 5000 IU/day of vitamin D from all available sources in order to optimize bone health by maintaining serum 25(OH)D levels of 75 to 80 nmol/L [84, 85, 94, 95]. This dosage would be unattainable from natural ultraviolet B (UVB) exposure during the months of October to April when residing in latitudes of 42.2 to 52° N [96] which is indicated by the high prevalence of vitamin D deficient indoor and outdoor athletes in a multitude of disciplines [24, 97,98,99]
In summary, an interesting theme has emerged from animal studies that supraphysiological dosages of vitamin D3 have potential ergogenic effects on the human metabolic system and lead to multiple physiological enhancements
Summary
Vitamin D, a fat-soluble vitamin, was first discovered in cod liver oil [1] and has since been identified as an essential vitamin, acting as a precursor steroid to a host of metabolic and biological processes. Once converted into its biologically-active form, 1,25-dihydroxyvitamin D [2], it regulates the expression of over 900 gene variants [3] These gene expressions have been shown to have significant impact on a wide variety of health and performance-related variables, such as exercise-induced inflammation, tumour suppressor genes, neurological function, cardiovascular health, glucose metabolism, bone health and skeletal muscle performance [4,5,6,7,8,9,10]. This 25(OH)D is hydroxylated by CYP27B1 (1α-hydroxylation) [29] This final step occurs primarily in the kidney [18], but various other tissues, namely skeletal muscle, have been shown to express CYP24A1 enzymes, where 25(OH)D becomes the active hormonal form, 1,25-dihydroxyvitamin D [29]. A more recent publication by Fitzgerald et al [41], concluded that there was no association between 25(OH)D levels and an individual’s
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