Mobilising vitamin D sequestered in adipose tissue in humans

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Up to half of people in the UK have low levels of vitamin D in their blood and finding ways to improve vitamin D status is a recognised health priority. Vitamin D is lipophilic (fat-loving) and accumulates in our adipose tissue (fat stores) in large amounts. The entrapment of vitamin D in adipose tissue contributes to low levels of vitamin D in blood. This is very relevant as most people in the UK are overweight and by 2035 almost half the population is predicted to be obese. Thus, a key challenge now and in the future is to find ways to successfully mobilise vitamin D from adipose to help reduce the impact of adipose expansion on the availability of vitamin D. Our preliminary data indicate that physical activity is an effective way to mobilise vitamin D from adipose tissue - even without weight loss. These preliminary data show that exercise has a powerful effect on the concentration of the important form of vitamin D in blood and that exercise stimulates the release of this form of vitamin D from adipose tissue. Based on these observations, we propose that regular exercise will improve the mobilisation of vitamin D from adipose tissue and that this will increase the amount and availability of the important form of vitamin D in blood. In this project, we will use a 12-week randomised controlled trial in men and women to examine the impact of exercise (versus control) on vitamin D status and metabolism in obesity. We will assess the impact of exercise on the various forms of vitamin D that are found in blood, and whether these changes lead to an improvement in the function of cells known to be affected by vitamin D status (a type of white blood cell called monocytes). We will use stable isotopes (non-radioactive tracers) to examine how the turnover of vitamin D is affected by exercise. By taking small biopsies of adipose tissue we will be able to examine the impact of exercise on the ability to mobilise vitamin D from adipose. This will also allow us to understand the biological pathways and mechanisms that are involved in vitamin D mobilisation and how they are affected by exercise. We have designed our research to include a lean comparator group so that we can understand the independent effects of obesity and exercise on vitamin D mobilisation, status and metabolism. This research will help us to understand the impact of exercise on vitamin D status and whether increasing physical activity represents a potentially useful strategy to mobilise vitamin D from adipose tissue. Understanding whether (and how) vitamin D can be mobilised from adipose tissue has been identified by key stakeholders, including agencies that inform the UK government, as an important knowledge gap. Thus, this research will have great potential for translation into policies and guidance related to vitamin D and health. In the future, we envisage that the benefits of exercise can be promoted as an adjunct strategy to improve population and individual vitamin D status alongside complementary strategies such as dietary supplementation. The outcomes from our research will also have implications for policies and guidance around the effects of obesity and physical inactivity on health. In addition to these direct effects on policies and practices, an understanding of the fundamental biological pathways and mechanisms through which physical activity helps to mobilise compounds sequestered in adipose tissue could provide the basis for novel pharmacological and non-pharmacological strategies, interventions and products related to vitamin D and other lipophilic compounds sequestered in adipose.