| Summary: | Elevated inflammation is associated with several chronic diseases, including obesity. Exercise is an established effective treatment of this condition by decreasing adiposity and independently regulating inflammatory pathways. The potential for vitamin D to confer anti-inflammatory benefits has been explored in cell culture studies, but few have explored its action at the whole body level. PURPOSE: To investigate the relationship between inflammatory markers in trained and untrained individuals with vitamin D levels either above or below a suggested optimal concentration. METHODS: College-aged females (N = 63), both trained and untrained, reported to the lab four times: to assess body size and composition, for blood collection, for a maximal aerobic test, and a test of anaerobic power. Blood was analyzed for serum 25OHD and CRP concentrations, stimulated with LPS to assess IL-6 production. Samples were prepared for FACS analysis for CD14, CD16, and TLR4 expression. RESULTS: Trained individuals presented with higher 25OHD levels, even prior to stratification into high and low groups (p = 0.015). VO2peak was significantly higher (p < 0.0001) and fatigue during the test for anaerobic power was significantly lower (p = 0.021) in trained individuals. Untrained individuals had a higher average body weight (p = 0.039) and estimated percent body fat (p = 0.011) compared to trained individuals, although the average estimated percent body fat of both groups was higher than the recommended level for this age group. Additionally, measures of sun exposure were negatively correlated with measures of body size and composition, although these relationships did not exist between serum 25OHD. CONCLUSION: In this study, regular physical activity was associated with higher serum 25OHD, lower BMI, waist circumference, and estimated percent body fat as well as reduced LPS-stimulated IL-6 production. Optimal vitamin D status did not appear to provide any additional health related or anti-inflammatory benefit in those with regular physical activity habits. However, in individuals not participating in a regular exercise program, the potential for vitamin D to mediate inflammation appeared more likely. More specifically, untrained people with optimal vitamin D status had lower numbers of total monocytes, CD14+CD16- cells, and decreased TLR4 expression on CD14+CD16+ cells; however, these differences did not translate into a change in overall cell function or markers of systemic inflammation as there was no difference between optimal and suboptimal groups with respect to LPS-stimulated IL-6 production or resting CRP concentrations. An expanded exploration of the relationship between vitamin D and inflammation may include assessing other inflammatory biomarkers, immune cell types, the vitamin D receptor, and the role of adipose tissue.
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