Personalized Definition of Short Sleep Using Long-Term Wearable Sleep Distributions

Study Objectives: To evaluate a framework using wearable data to personalize the definition of short sleep, comparing its temporal and functional characteristics against a fixed threshold. Methods: 462 healthy adults wore sleep trackers and provided daily ecological momentary assessments for a year. Short sleep was defined using either a fixed threshold of <6 h/night (fSS) or personalized thresholds anchored to individual sleep-duration distributions (pSS). Temporal patterns of consecutive short-sleep nights were characterized. Linear mixed-effects models examined associations between accumulating short-sleep nights and short- and long-term markers. Sleep patterns across six other countries were also evaluated. Results: pSS and fSS produced similar average thresholds and overall prevalence of short-sleep nights. However, pSS showed larger effect estimates for short-term outcomes, including alertness, sleep satisfaction, stress, sleep heart rate, HRV, and sedentariness. Effects increased with successive short-sleep nights. Proportion of pSS showed stronger association with blood pressure and arterial stiffness. Isolated short nights were common, whereas longer runs were uncommon and typically followed by incomplete recovery sleep. Personalized thresholds distinguished stable short sleepers with few pSS nights from individuals experiencing recurrent sleep shortfall and highlighted vulnerability among those achieving recommended sleep duration but with high variability. Despite marked cross-country differences in sleep habits, the distribution of short-sleep runs, and termination patterns were remarkably similar. Conclusion: Anchoring short sleep to individual habitual sleep distribution captures relative sleep shortfall beyond absolute duration, better characterizing the functional impact of short sleep. Preventive strategies may benefit from limiting pSS accumulation together with addressing sporadic inadequate sleep.