The Effects of Vitamin D Supplementation on Aerobic Exercise Performance in Healthy Adults

Abstract

Background: Vitamin D was once only thought to be beneficial for bone disorders. However, recently evidence has shown that almost every body tissue expresses vitamin D receptors. These are involved in many other bodily functions which are still to be fully understood. Evidence shows that vitamin D is involved in many effects throughout the body which are involved in enhancing sport. There have been very little studies done to determine if vitamin D has an effect on aerobic exercise. Recently evidence has suggested that vitamin D may influence aerobic performance by having an effect on erythropoietin resistance, muscle and blood pressure. Objective: The aim of this study is to examine the effects of short term vitamin D supplementation for 2 weeks on aerobic exercise in healthy adults aged 18-50 years. Methods: A single blinded clinical trial was carried out on healthy adults (n=11) over 21 days which included a 14 day supplementation period of either 50__g of Vitamin D (n=6) or placebo (un-medicated sucrose) (n=5). The trial consisted of a baseline 15 minute run on a treadmill with a 1.5% incline, a supplementation period, followed by another 15 minute run with a 1.5% incline. Activity and diet diaries where completed throughout the study. Measurements of height, weight, blood pressure, heart rate, blood lactate and rating of perceived exertion were recorded at baseline and day 21 of intervention before and after each run. Results: There were no significant differences in dietary vitamin D intake or physical activity level before and during the intervention (P=0.72; P=0.67). Vitamin D intakes in placebo and supplementation groups before (P=0.70) and during the intervention (P=0.20) showed no significant differences. Percentage of maximum heart rate significantly decreased following supplementation (P=0.02), the placebo group showed no significant difference (P=0.41). No significant difference was found for either the supplement or placebo group for average heart rate before and after the intervention (P=0.09; P=0.68). Interestingly, physical activity level was found to have a moderately negative relationship with differences seen in maximum percentage heart rate (R= -0.62) before and after vitamin D supplementation. There were no significant reductions in blood lactate following the intervention in the supplement or placebo group (P=0.17; P=0.84). There were also no significant reductions in systolic (P=0.59) or diastolic blood pressure (P=0.55) after the run following supplementation. No significant reductions in systolic or diastolic blood pressure were found following the placebo either (P=0.15; P=0.34). A very significant difference was found in rating of perceived exertion before and after vitamin D supplementation (P=0.001). Conclusions: Short term vitamin D supplementation significantly reduced rating of perceived exertion and percentage of maximum heart rate during aerobic exercise. Although not significant vitamin D also reduced blood pressure, average heart rate and blood lactate following aerobic exercise. The amount of vitamin D supplementation needed to produce beneficial effects requires further study. However, vitamin D was found to affect cardiovascular, bone, muscular and fatigue parameters necessary to enhance aerobic performance. Keywords: vitamin D, supplementation, aerobic exercise, blood pressure, heart rate, blood lactate.