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The Impact of Vitamin D Status upon Markers of Athlete Health

Allison, R (2017) The Impact of Vitamin D Status upon Markers of Athlete Health. Doctoral thesis, Liverpool John Moores University.

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Abstract

Introduction At present there is a pandemic of low serum vitamin D (25[OH]D) concentration, partly due to a lack of sun exposure (the primary route for synthesis) and modern lifestyle choices. The bioactive form of vitamin D, 1,25-dihydroxyvitamin D (1,25[OH]2D3) exerts its biological activity by binding to the vitamin D receptor (VDR). These receptors play a central role in the biological actions of vitamin D and are expressed in nearly every tissue and cell type in the body (M. Holick, 2007). Vitamin D deficiency is widespread within many general and athletic populations and associated with a number of detrimental health conditions, including a long-term impact on cardiovascular health (M. Holick, 2007; Larson-Meyer & Willis, 2010; Pittas, Lau, Hu, & Dawson-Hughes, 2007), and the aetiology of osteomalacia and osteoporosis (M. F. Holick, 2009). Given the prevalence and potential negative morbidity associated with deficiency (Larson-Meyer & Willis, 2010), regular vitamin D testing has been recommended as part of routine athlete screening. Current literature shows inconsistent associations between vitamin D status and bone mineral density and cardiac health; (Bischoff-Ferrari, Kiel, et al., 2009; Marwaha et al., 2011) particularly in racial minorities and athletic populations. Whilst it is considered that athletes should have ‘sufficient’ vitamin D concentrations, the exact value to ‘optimise’ health is equivocal. Finally, there appears to be a ‘paradoxical relationship’ between ethnicity and vitamin D concentration, that has largely been ignored, i.e. blacks generally present with the lowest vitamin D concentrations but the greatest bone mineral density (BMD) and reduced risk of fracture (Cauley et al., 2005). Vitamin D–binding protein (DBP) may account for observed racial differences in manifestations of vitamin D (Powe et al., 2013). To date, research on vitamin D status in athletes has overlooked DBP. Whilst there are data that support the associations between vitamin D and markers of bone and cardiac health in the general population, definitive relationships in the athletic population are yet to be established. Therefore, the aim of this thesis was to examine the relationship between vitamin D and measures of bone mass and cardiac structure and function within a large, ethnically diverse cohort of healthy athletes, with a focus to the role of DBP in determining racial differences in bioavailable levels. Studies 1. Oral vs. Intramuscular Vitamin D Supplementation for Treating Insufficient Athletes 2. No Association between Vitamin D Deficiency and Markers of Bone Mass in Athletes 3. No Association between Vitamin D Status and Markers of Bone Mass in Non-Weight Bearing Athletes 4. Why don’t serum Vitamin D concentrations associate with BMD by DXA? A case of being ‘bound’ to the wrong assay? Implications for Vitamin D screening 5. Severely Vitamin D-Deficient Athletes Present Smaller Hearts than Sufficient Athletes Methodical overview Male athletes registered with the Qatar Olympic Committee (QOC) presented for pre-competition medical assessment at Aspetar Sports Medicine Hospital, Qatar. All athletes completed a vitamin D questionnaire that included questions specifically related to country of origin, sporting discipline, skin type, self-reported exposure to daily sunlight, use of sunscreen, dietary supplements and/or medication, and an assessment of skin colour. All individuals undertook bone densitometry and body composition analysis by dual-energy x-ray absorptiometry (DXA; Osteocore III, Perols, France, version 5.22b). Venous blood samples were collected from athletes following an overnight fast and was analysed for PTH, calcium, albumin and serum 25[OH]D. Athletes were split into four 25[OH]D categories; severely deficient (<10 ng/mL), deficient (10–20 ng/mL), insufficient (20–30 ng/mL), or sufficient (>30 ng/mL). Serum vitamin D binding protein (DBP) concentrations (μg/mL) were determined using a commercially available kit (R&D Systems, UK). Free, bioavailable, and DBP-bound 25[OH]D were calculated using equations from supplementary material of (Powe et al., 2013). Lastly, all individuals assessed for family history of cardiovascular disease and personal symptoms, with a physical examination, 12-lead electrocardiogram and an echocardiogram. Results The key findings from the thesis are 1) serum 25[OH]D concentrations are not associated with markers of bone mass 2) bioavailable vitamin D is a better preceptor of BMD that serum 25[OH]D concentration and 3) severely 25[OH]D deficient athletes present with smaller cardiac structure that sufficient athletes. Conclusion In a healthy, ethnically diverse athletic population, there is no relationship between serum 25[OH]D concentration and makers of bone mass, regardless of sporting type and that bioavailable vitamin D is a better predictor of bone mineral density. Suggesting that our chosen method of assessment may not be appropriate to identify true deficiencies. Systematic screening to determine 25[OH]D concentrations is expensive, and demonstrates a poor relationship to bone mass in an ethnically diverse athletic population. It can be argued that vitamin D testing should be reserved for the symptomatic athlete (i.e. musculoskeletal injury, REDs). In turn, prophylactic vitamin D supplementation (2000IU/d D3) to ‘correct’ insufficient athletes with normal bone health can be questioned, since supplementation recommendations are based on a measure that is not associated with bone health. Severely 25[OH]D deficient athletes present with smaller (<10 ng/ml) presented significantly smaller cardiac structures than insufficient (20–30 ng/ml) and sufficient (>30 ng/ml) athletes. The precise mechanism(s) causing this cardiac hypertrophy (or in our case, lack of hypertrophy) in the 25[OH]D-deficient state remains unclear. Clinically low vitamin D concentrations are detrimental to aspects of health that influence athletic performance. Therefore, the widespread prevalence of low serum 25[OH]D concentrations should not be ignored. However, vitamin D metabolism is a rapidly evolving field, with the prospect of a more complete picture of this complex endocrine system becoming ever so closer. The challenge for future research is to determine ethnically specific concentration ranges and evidenced based guidelines for the diagnosis and treatment of ‘true’ vitamin D deficiency and its impact on athlete health and performance.

Item Type: Thesis (Doctoral)
Uncontrolled Keywords: Vitamin D; Athlete Health; Bone; Cardiac Structure
Subjects: R Medicine > RC Internal medicine > RC1200 Sports Medicine
Divisions: Sport & Exercise Sciences
Date Deposited: 17 Jan 2018 09:57
Last Modified: 17 Jan 2018 09:58
DOI or Identification number: 10.24377/LJMU.t.00007861
Supervisors: Close, G and Wilson, M
URI: http://researchonline.ljmu.ac.uk/id/eprint/7861

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