Cardiorespiratory Fitness, Serum 25-hydroxyvitamin D, and Risk of Metabolic Syndrome Among Men: The Cooper Center Longitudinal Study

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PURPOSE: We examined the individual and joint associations among cardiorespiratory fitness (CRF), serum vitamin D [25(OH)D], and metabolic syndrome (MetSyn). METHODS: Between 2006 and 2018, 14349 apparently healthy men completed a comprehensive health examination. Measures included CRF based on a maximal treadmill exercise test, components of MetSyn, and 25(OH)D. Participants were classified into categories of low (quintile 1), moderate (quintiles 2-3), and high (quintiles 4-5) CRF by age group, as well as by clinical cut points for MetSyn and 25(OH)D. We examined mean 25(OH)D levels in men with and without MetSyn. We calculated odds ratios (OR) of MetSyn across levels of CRF and 25(OH)D, and also examined joint associations among these three variables. RESULTS: The prevalence of 25(OH)D deficiency and MetSyn was 16.9% and 22.2%, respectively. Mean 25(OH)D levels were 30.9 + 11.6 and 26.3 + 10.7 ng/mL in men without and with MetSyn, respectively (p<.001). Prevalence of MetSyn was inversely associated with ordered categories of CRF and 25(OH)D (p for trend <0.001 for both). Men with normal 25(OH)D had lower odds of MetSyn than men who were vitamin D deficient (OR=0.29, 95% CI=0.26-0.33). Men with moderate (OR=0.31, 0.27-0.35) or high CRF (OR=0.08, 0.07-0.09) had lower odds of MetSyn than men with low CRF. Joint associations between CRF, 25(OH)D, and MetSyn revealed significantly greater prevalence of MetSyn in unfit men when compared to fit men within each category of 25(OH)D (p<0.001). Each 5 ng/mL increment of 25(OH)D, and 1 MET increment of CRF was associated with a 16.0% and 31.3% lower prevalence of MetSyn, respectively. CONCLUSION: There are strong individual and joint associations between CRF, 25(OH)D, and MetSyn. Although these observed associations are cross-sectional, it seems prudent to recommend increased levels of physical activity and vitamin D intake in men with low CRF, vitamin D deficiency, and/or MetSyn.