Background: Use of accelerometers to objectively measure physical activity (PA) and sedentary behavior (SB) in epidemiologic studies may improve understanding of associations with CVD, particularly in older adults. This cross-sectional study examined associations between accelerometer measures of PA and SB with cardiovascular health in 4870 race-ethnically diverse postmenopausal women, ages 63 to 99 years (mean 78.9) enrolled in OPACH, an ancillary study of the Women’s Health Initiative program.
Methods: Vector magnitude counts per 15-sec epoch from hip worn triaxial accelerometers (minimum of 4 days with ≥10 hours/day wear time) were used to define time spent in SB (0-18 counts/15 sec), low light intensity (19-225), high light intensity (226-518), and moderate-to-vigorous intensity PA (MVPA; ≥519) based on count cutpoints determined from a laboratory calibration study among women of similar age. Predicted 10-year risk of CVD was computed using the Reynolds risk score (RRS), for which higher values reflect higher predicted CVD risk. Relationships between SB, PA and RRS were examined using generalized linear model analyses, adjusting for accelerometer wear time.
Results: The mean RRS was 13.7±11.9 (range 0.8 to 94.3). Based on regression analysis, every hour/day spent in SB was associated with an average 2.3% increase in the RRS. In contrast, every hour/day spent in low-light, high-light, or MVPA resulted in an average 1.1%, 1.5%, and 5.2% reduction, respectively, in the RRS. A significant positive association was observed between SB and decile of RRS (trend, p<.0001); whereas, significant inverse gradients for time spent in each PA level were observed across decile of RRS (trend, p<.001 for all). Mean hours/day associated with the lowest and highest decile of RRS, respectively, were 12.0 and 13.1 for SB; 3.6 and 3.1 for low light; 1.9 and 1.4 for high light; and 1.3 and 0.6 for MVPA. These patterns of association for SB and PA with RRS were also observed when stratified by race-ethnicity and age.
Conclusion: Based on objectively assessed SB and PA, this study confirms that prolonged SB is adversely related with cardiovascular health in older women. Results further suggest that even light intensity PA could have cardiovascular benefit in older women. Because a large proportion of daily activity time is spent at lower intensity among older adults, this finding has important public health implications. Prospective studies are needed to confirm these cross-sectional results.