Fluctuations in Sleep Duration and Timing and Cardiometabolic Risk.

Sleep behavior has emerged as an important determinant of cardiometabolic health. However, to date, much attention has focused on sleep duration with accumulating evidence resulting in leading medical organizations to include adequate sleep duration in their recommendations for disease risk prevention and health promotion. However, sleep is a multidimensional construct that extends beyond sleep duration and includes factors related to the variability of duration but also to the regularity in its timing across days. These concepts, termed sleep duration variability (day-to-day differences in sleep amounts) and sleep timing regularity (day-to-day differences in sleep timing), can influence the circadian system and have independent health effects beyond sleep duration per se. Here, we assess the literature evaluating the association of fluctuations in sleep behaviors over time and cardiometabolic risk factors and their potential implications for chronic disease development. We conclude that large-scale population-based studies support an adverse relation between fluctuations in sleep behaviors and cardiovascular disease risk markers, but caution that causality should be evaluated in clinical intervention studies.