Does Cardiorespiratory Fitness Modify The Association Between Sitting Time And Cardiometabolic Risk Factors?

Abstract

PURPOSE: To examine the association between sitting time and cardiometabolic risk factors in healthy men and women and explore the potential modifying role of estimated cardiorespiratory fitness (CRF). METHODS: A cross-sectional analysis of 4,486 men and 1,845 women enrolled in the Cooper Center Longitudinal Study for the period 2010-2013 was conducted. Sitting time was self-reported as about 0%, about 25%, about 50%, about 75%, and about 100%. CRF was estimated from time spent on a maximal exercise treadmill test and expressed as metabolic equivalents. Risk factors were defined as follows: Total cholesterol >200 mg/dL; LDL cholesterol >100 mg/dL; HDL cholesterol <40 mg/dL for men and <50 mg/dL for women; Triglycerides ≥150 mg/dL; Fasting blood glucose ≥ 110 mg/dL. Hypertension was defined as a systolic blood pressure ≥130 mmHg and /or diastolic blood pressure ≥85 mmHg. The composite outcome of metabolic syndrome was defined as meeting ≥3 of the criteria above. Sex-specific multivariable models were constructed to examine the association between sitting time and each outcome adjusted for covariates, including age, smoking status, and alcohol consumption. A cross product term of sitting time and CRF was included in the full model to assess the possibility of effect modification. RESULTS: In unadjusted analysis, outcomes did not vary across categories of sitting time in men. For women, low HDL cholesterol, elevated triglycerides, and the presence of metabolic syndrome significantly increased as sitting time increased. However, after adjustment for CRF and other covariates, the associations between sitting time and risk factors were no longer statistically significant. For example, women who sat about 75% of the time were no more likely to have metabolic syndrome (OR: 1.66; 95% CI: 0.59, 4.64) than women who sat 0% of the time. Finally, the sitting time x CRF interaction terms did not reach statistical significance for any outcome, regardless of sex. CONCLUSION: In this healthy group of men and women, sitting time was not associated with risk factors after adjustment for CRF and other covariates. In addition, CRF did not appear to modify this association for either sex. These findings do not support previous work demonstrating independent associations of sitting time on cardiometabolic risk factors or metabolic syndrome.