Associations Between Workday/Leisure Day Lifestyle Behavior and Cardiovascular Disease Risk Factors Among Night Shift Workers Using the Isotemporal Substitution Model

<b>Background/Objectives</b>: Night shift workers (NSWs) are at a high risk of cardiovascular disease (CVD). However, the association between CVD risk factors and lifestyle behavior (sedentary behavior [SB], physical activity [PA], and sleep) is unclear among NSWs. NSWs lead different lifestyles on workdays and leisure days. This study aimed to investigate the association between lifestyle behavior times and CVD risk factors among NSWs during workdays and leisure days using an isotemporal substitution model. <b>Methods</b>: This cross-sectional study included 66 male NSWs. Time spent on lifestyle behaviors was obtained using a tri-axial accelerometer and classified into SB, light-intensity PA, moderate-to-vigorous PA (MVPA), and sleep. Lifestyle behavior times were divided into workdays and leisure days. CVD risk factors were determined based on periodic health checkups. An isotemporal substitution model was used to estimate the effect of replacing one lifestyle behavior with another on CVD risk factors. <b>Results</b>: The lifestyle behavior times differed between workdays and leisure days. On workdays, reallocating 30 min of SB to light-intensity PA was significantly associated with a lower waist circumference. In addition, reallocating sleep to SB or MVPA was significantly associated with higher triglyceride levels. On leisure days, reallocating SB or sleep time to MVPA was significantly associated with lower aspartate aminotransferase levels. <b>Conclusions</b>: Given the difference in the associations between lifestyle behavior times and CVD risk factors among NSWs between workdays and leisure days, NSWs should be mindful of the time spent on SB, PA, and sleep on workdays and leisure days to achieve healthier outcomes.