Abstract Body: Introduction: Current physical activity (PA) recommendations support replacing time spent sedentary with PA of any intensity. Replacing sedentary time with light intensity PA (LPA) may be a more accessible behavior change for many individuals compared with increasing moderate/vigorous intensity PA (MVPA). However, the longitudinal associations of replacing sedentary behavior with LPA and cardiometabolic health are not clear.
Hypothesis: We hypothesized that replacing time spent sedentary with LPA is associated with improvement in cardiometabolic risk across midlife.
Methods: Participants in the CARDIA study with accelerometer and cardiometabolic biomarker data at Year 20 (2005-06) and Year 35 (2020-22) study visits (n=996) were included in this analysis. Waist circumference, mean arterial pressure, fasting glucose, fasting insulin, triglycerides, and HDL cholesterol were standardized and averaged to create a z-score, where higher scores represent worse cardiometabolic health. We used compositional isotemporal substitution models to estimate changes in cardiometabolic risk score resulting from replacement of sedentary time with LPA and whether associations varied by initial sedentary time or MVPA level.
Results: Across midlife (mean 45±SD 3.5 [Y20] to mean 60±SD 3.6 [Y35] years old), mean cardiometabolic risk score increased by 0.03 SD. In those with initially low sedentary time, replacing 1 hour of sedentary time with LPA from Y20 to Y35 was associated with a -0.03 SD change in cardiometabolic risk score (95% CI: -0.06, -0.004; Figure) across the same time period. In those with initially high sedentary time, associations were attenuated and not statistically significant (-0.02; 95% CI: -0.04, 0.004). Associations were stronger with more time reallocated (up to 3 hours) and similar in those with low and high MVPA.
Conclusions: Model-based replacement of sedentary time with LPA was associated with attenuation of age-related decline in cardiometabolic health across midlife.