Abstract 022: Exploring the 24 Hour Day: using Isotemporal Substitution to Model the Cardiometabolic Benefits of Sleep Duration in Older Women

Background: Sleep, sedentary behavior (SB), and physical activity (PA) are independently associated with cardiometabolic health, but few studies have examined the interrelationships between 24 hour activity and cardiometabolic risk factors. Extending sleep may be a feasible cardiometabolic risk reduction strategy; however, research is needed to understand how replacing time in SB and/or PA with sleep impacts cardiometabolic risk. Methods: Women’s Health Initiative participants in the OPACH Study (N=3329; mean age=78.5±6) wore ActiGraph GT3X+ accelerometers 24 hours/day for up to 7 days. Sleep duration was derived using a validated protocol. Adjusted regression models estimated the relationship between sleep duration and cardiometabolic markers. Separately for shorter (<8 hours) and longer (≥8 hours) sleepers, isotemporal substitution models estimated the change in cardiometabolic risk markers associated with reallocating time in daytime activity (SB, light PA (LIPA), moderate to vigorous (MVPA)) to or from sleep. Results: Longer sleep duration was significantly associated with higher insulin, HOMA-IR, total cholesterol, triglycerides, and Reynolds Risk Score (RRS) (all p < 0.05). For shorter sleepers, reallocating 33 minutes of MVPA to sleep was associated with significantly higher values of insulin, HOMA-IR, triglycerides, waist circumference, and RRS (0.9%-11.4%) (Figure 1). Replacing 91 minutes of SB time with sleep was associated with significantly lower waist circumference (-1%). In longer sleepers, reallocating 74 minutes from sleep to LIPA was associated with significantly lower values of insulin, HOMA-IR, trigylcerides, and waist circumference (-1.4% - -12.3%). Conclusions: This is one of the first isotemporal analysis to include objectively measured sleep duration. Results illuminate possible cardiometabolic risks and benefits of reallocating time to or from sleep duration.