The Joint Effects of Cardiorespiratory Fitness and Waist Circumference on All-Cause Mortality in Women

Abstract

When examined separately, cardiorespiratory fitness (CRF) and waist circumference (WC) are independently associated with all-cause mortality. However, the joint effect of CRF and WC on mortality in women is unclear. PURPOSE: To examine the relation between CRF and WC, together in the same model, and all-cause mortality in a large cohort of women. METHODS: Participants were 8383 women (age = 44±10 years; WC = 74±11 cm) who completed a preventive medical examination between 1979 and 2002. CRF was quantified as duration of a symptom-limited maximal treadmill test. CRF categories were based on age- and sex-specific distributions of exercise duration defined as low (lowest 20%), moderate (middle 40%) and high (highest 40%) fitness. WC was measured at the umbilicus and tertiles of the WC distribution were as follows: low (< 67 cm), moderate (67-74.5 cm) and high (>74.5 cm). We conducted mortality follow up through 2004 primarily using the National Death Index. RESULTS: After an average follow-up period of 11.5 years, mortality was confirmed in 2.2% (n=186) of women. Age-adjusted mortality rates per 10,000 person-years of follow up across low, moderate and high CRF categories were 42.9, 17.6 and 13.7 for women in the high WC group, 27.9, 15.0 and 22.7 for the moderate WC group and 24.9, 24.0 and 6.9 for the low WC group. Results from a proportional hazards regression model that included age, health and smoking status, showed CRF was inversely related to the risk of all-cause mortality regardless of WC. In this model, women in the moderate and high CRF groups had a 40-50% lower mortality risk compared to low fit women. Hazard ratios (95% CI) for mortality were 0.56 (0.39-0.80) and 0.46 (0.31-0.68) among moderately and highly fit women, respectively. Based on this analysis, there was no statistically significant relation between WC and mortality. CONCLUSIONS: Reduced risk for all-cause mortality in women is associated with moderate and high level CRF independent of WC.