The role of exercise and age on vitamin D metabolism

A low vitamin D status (determined by 25(OH)D concentration) has been identified as an association risk factor in the aetiology of numerous chronic diseases, with older adults identified as generally more deficient than younger populations. Accumulating data is suggestive that physical activity and exercise may influence 25(OH)D and vitamin D metabolites downstream in the complex metabolic pathway. Specifically, exercise has been shown to act as a direct and indirect stimulus on the intracellular vitamin D receptor (VDR), which mediates the effects of vitamin D and initiates genomic and non-genomic signalling responses. The role of physical activity and exercise on 25(OH)D concentration and VDR expression is not yet recognised in a healthy human population.This thesis aimed to establish whether there is a link between physical activity status and 25(OH)D concentration, and if there is a role of age and exercise on 25(OH)D concentration and VDR expression (as quantified in circulating systemic T lymphocytes).The main results demonstrate that 25(OH)D concentration is not influenced by age or cardiorespiratory fitness (CRF), however VDR expression declines with older age and a higher CRF predicts a greater expression of the VDR. It was found that a single bout of exercise acutely increases VDR expression in circulating T lymphocytes, with exercise modality appearing to influence the response. There was a more pronounced response observed following an endurance compared to a resistance exercise bout. The impact of the exercise-induced lymphocyte response on the observed changes in T cell VDR expression was explored, however they appear to be independent.In conclusion, the findings of this thesis support the notion that exercise could be used as a short-term strategy to increase cellular VDR expression in a human population