Mobilising vitamin D from adipose tissue: The potential impact of exercise

Abstract

Vitamin D is lipophilic and accumulates substantially in adipose tissue. Even without supplementation, the amount of vitamin D in the adipose of a typical adult is equivalent to several months of the daily reference nutrient intake (RNI). Paradoxically, despite the large amounts of vitamin D located in adipose tissue, individuals with obesity are often vitamin D deficient according to consensus measures of vitamin D status (serum 25-hydroxyvitamin D concentrations). Thus, it appears that vitamin D can become 'trapped' in adipose tissue, potentially due to insufficient lipolytic stimulation and/or due to tissue dysfunction/adaptation resulting from adipose expansion. Emerging evidence suggests that exercise may mobilise vitamin D from adipose (even in the absence of weight loss). If exercise helps to mobilise vitamin D from adipose tissue, then this could have important ramifications for practitioners and policymakers regarding the management of low circulating levels of vitamin D, as well as chronically low levels of physical activity, obesity and associated health conditions. This perspective led us to design a study to examine the impact of exercise on vitamin D status, vitamin D turnover and adipose tissue vitamin D content (the VitaDEx project). The VitaDEx project will determine whether increasing physical activity (via exercise) represents a potentially useful strategy to mobilise vitamin D from adipose tissue.

Keywords: 25(OH)D; 25‐hydroxyvitamin D; adipose; exercise; physical activity; vitamin D.

Figure 1

The amount of vitamin D present in adipose tissue is likely to be quantitatively important. When extrapolated, the amounts of vitamin D present in the adipose tissue of an individual weighing 100 kg and with a body fat percentage of 40% may equate to up to 2000 days of the daily recommended nutrient intake (RNI) of vitamin D (10 μg) from dietary sources or supplementation. [Colour figure can be viewed at wileyonlinelibrary.com]

Figure 2

(a) The effect of 30 minutes of cycling exercise at 70% $\dot{\mathrm{V}}{\mathrm{O}}_2\max$ on serum 25(OH)D concentrations in humans [redrawn using data from Sun et al. (2017)]. Data shown are mean ± standard error of the mean (SEM) for men and women combined. (b) Mean change in serum 25(OH)D concentrations following 30 minutes of cycling exercise at 70% $\dot{\mathrm{V}}{\mathrm{O}}_2\max$. Left‐hand bar represents change from pre‐exercise to immediately post‐exercise, right‐hand bar represents change from pre‐exercise to 24 hours post‐exercise [redrawn using data from Sun et al. (2017)]. (c) The effect of 5 weeks of progressive cycling endurance exercise (30 minute bouts, 3 bouts/week, from 60% to 75% $\dot{\mathrm{V}}{\mathrm{O}}_2\mathrm{peak}$) during winter months on serum 25(OH)D [redrawn using data from Sun et al. (2018)]. Data shown are mean ±SEM. (d) Mean change in serum 25(OH)D concentrations following 5 weeks of progressive cycling endurance exercise [redrawn using data from Sun et al. (2018)]. [Colour figure can be viewed at wileyonlinelibrary.com]

Figure 3

Vitamin D and the adipocyte. We hypothesise that in the rested or fed state triacylglycerol and vitamin D metabolites are trapped in the lipid droplet of adipocytes. When exposed to a lipolytic stimulus, triacylglycerol is liberated and this may coincide with mobilisation of vitamin D metabolites. ATGL, adipose triglyceride lipase; HSL, hormone‐sensitive lipase, TAG, triacylglycerol. [Colour figure can be viewed at wileyonlinelibrary.com]