The impacts of vitamin D status and HIIT on physical performance and frailty during aging

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The impacts of vitamin D status and HIIT on physical performance and frailty during aging Frailty is a progressive age-associated condition that raises susceptibility to disability, hospitalization, and death and may affect as many as 10% of the 50 million individuals currently over the age of 65, and nearly 70% of those over the age 85. Inactivity and vitamin D insufficiency are also highly prevalent in older populations, and both are correlated with frailty. High intensity interval training (HIIT) may be a novel therapeutic strategy as HIIT safely provides substantial strength and endurance benefits with lower time commitments. The goals of this project are to characterize the role of vitamin D supplementation in age-related frailty, and whether vitamin D status can mediate the response to HIIT. Additionally, this project will investigate the role of muscle stem cells and underlying microRNA (miRNA) signaling in mediating this response. Vitamin D insufficiency from 6 to 18 months of age in mice leads to declines in physical performance. Additionally, HIIT enhances physical performance and reduces frailty in mice exercised from 24 to 28 months of age (equivalent to a 65-80 year old human). The hypothesis of this proposal is that vitamin D sufficiency is necessary to optimize stem cell function, physical performance, and the response to exercise, as well as reduce frailty during aging. To test this hypothesis, vitamin D sufficient mice will be compared to those that are vitamin D insufficient in terms of physical performance and frailty during aging and in the response to HIIT. This study will address critical gaps in the vitamin D field, which is stymied by conflicting studies regarding the role of vitamin D in regulating physical performance, frailty, and the response to exercise. The use of a mouse model in this study will allow an understanding of the longitudinal impacts of HIIT and vitamin D over the human equivalent of decades, which are otherwise difficult to determine in clinical studies due to length as well as the obfuscating contributions of lifestyle and genetic confounders. Findings from our proposed study will provide a clinical trial blueprint for successful implementation of exercise and vitamin D supplementation, thus improving the quality of care for our aging population.