Association of Increased Cardiorespiratory Fitness with Low Risk for Clustering of Metabolic Syndrome Components in Asymptomatic Men

Background: From a preventive aspect, it is especially important to investigate the lifestyle risk factors associated with cardiovascular disease (CVD). The purpose of this study was to determine the relationship of increasing metabolic syndrome (MS) components across increasing levels of estimated cardiorespiratory fitness (CRF) in asymptomatic young to middle-aged men. Methods: We studied 449 consecutive asymptomatic men (47 ± 7 years) who underwent a maximal treadmill exercise test according to the Bruce protocol. Cardiorespiratory fitness (CRF) was divided into tertiles based on metabolic equivalents (METs). The following MS components were studied: 1) waist circumference >102 cm; 2) serum triglycerides ≥150 mg/dL; 3) HDL cholesterol levels of <40 mg/dL; 4) fasting blood glucose (FBG) ≥110 mg/dL or 5) blood pressure ≥130/85 mmHg or treated hypertension. Multinomial logistic regression was used to investigate the relationship between clustering of MS components and CRF as determined by metabolic equivalents (METs). We used polytomous logistic regression to determine the likelihood of clustering of increasing components of metabolic syndrome with intermediate (2^nd tertile) and low (1^st tertile) levels of CRF as compared to those with highest levels of CRF (3^rd tertile). Results: Overall in the study population, zero, 1, 2 and ≥3 (i.e., metabolic syndrome) risk factors for MS were observed in 29% (n = 129), 26% (n = 118), 22% (n = 98) and 23% (n = 104) men, respectively. The mean METS achieved in the study population was 10 ± 2 (range 4-20). Nearly half (49%) of individuals with the highest levels of CRF had no MS risk factors whereas only 18% of those with low CRF (METS <9) had no MS risk factors. On the other end of the spectrum, the prevalence of MS (≥3 MS risk factors) increased significantly across decreasing levels of CRF (6, 22, 33% p <0.0001 for trend). Multivariable polytomous logistic regression (adjusting for age, smoking, cholesterol-lowering therapy) demonstrated that individuals with low CRF (1^st tertile of METS) compared to those with highest CRF had 3.1- (p = 0.001) and 11.8- (p <0.0001) fold higher risk of having 2 and ≥3 MS components, respectively. Similar results were observed when the analyses was repeated adjusting for Framingham risk score. Conclusions: Asymptomatic men with low levels of CRF have a greater likelihood for clustering of MS components and thus are at higher CVD risk. Further studies are needed to define the risk of cardiovascular disease in patients with intermediate levels of CRF and address which treatment strategies are most important given an individual's risk profile.