Cardiorespiratory fitness and coronary artery calcification in women

Introduction: Cardiorespiratory fitness (fitness) has been shown to be inversely associated with coronary heart disease morbidity and mortality. The cardioprotective mechanisms of fitness are not well defined. The goal of this study was to assess the relationship between coronary artery calcification as a measure of atherosclerotic burden and fitness in a large population of generally healthy women. Methods: 5341 women ages 40-90 years seen between 1997 and 2007 underwent maximal treadmill exercise testing and coronary artery calcium (CAC) scanning. Fitness was reported in METs estimated from maximal treadmill time, grade, and speed. CAC was characterized dichotomously as CAC=0 versus CAC>0, and CAC<100 versus CAC≥100. Multiple logistic regression models were used to calculate the adjusted odds ratio of any CAC (CAC>0) and CAC≥100. Fitness was added to these models continuously and categorically based on standard and sample-specific cut-points. Results: With a mean age of 52.0 years, the overall prevalence of detectable CAC was 19.9% and CAC≥100 was 6.8%. Univariable analysis showed a modest inverse relationship between fitness and CAC>0 (24% in low fit versus 19% in high fit, p-trend=0.006), with a similar trend observed for CAC≥100. In multivariable models, age adjustment diminished this association and the relationship was no longer statistically significant after adjustment for traditional risk factors. Conclusions: The cardioprotective benefit of fitness does not appear to be mediated by an effect independent of traditional risk factors on the development of calcified coronary atherosclerosis as measured by electron beam tomography.