A 15-week vitamin D supplementation and indoor cycling intervention reduces exercising heart rate, with no effect on glycaemic control in healthy adults: A pilot investigation

Significant positive correlations are often observed between vitamin D concentrations and physical activity levels. Whilst this may be due to individuals who are physically active spending time outdoors (i.e. increased opportunity for vitamin D synthesis), there is growing evidence to suggest a more complex relationship between vitamin D status, physical fitness and health outcomes. To explore this further thirty-nine healthy adults were randomly allocated to 15 weeks of exercise training (Ex), no training (NoEx), 2000 IU/day vitamin D (VitD) and/or placebo (Pla) supplementation (giving four possible allocations: NoEx+VitD; NoEx+Pla; Ex+VitD; Ex+Pla). Vitamin D status, glycaemic control and exercise responses were measured pre- and post-intervention. A series of 2 x 2 ANOVAs failed to find any effect of supplementation or exercise on any of the measures except heart rate during low intensity exercise, and vitamin D status. Heart rate was significantly reduced (6%, p < 0.05) in the Ex+VitD group. Vitamin D status was significantly raised (28%, p < 0,05) in the supplementation groups (NoEx+VitD and Ex+VitD) at a time of year (August-November) when a seasonal decline was observed in the placebo groups (33%, p < 0.05). These findings indicate that vitamin D supplementation (2000 IU/day) may have an enhancing role alongside exercise in inducing cardiorespiratory adaptations to exercise training. Further investigations are required to confirm these findings and identify the mechanisms involved.