Self-Reported Sleep Duration and Time in Bed as Predictors of Physical Function Decline: Results from the InCHIANTI Study

Study Objectives: To characterize elderly persons into sleep/rest groups based on their self-reported habitual total sleeping time (TST) and habitual time in bed (TIB) and to examine the prospective association between sleep/rest behavior on physical function decline. Design: Population-based InCHIANTI study with 6 years follow-up (Tuscany, Italy). Setting: Community. Participants: Men and women aged >= 65 years (n = 751). Measurements and Results: At baseline, participants were categorized into 5 sleep/rest behavior groups according to their self-reported TST and TIB, computed from bedtime and wake-up time Physical function was assessed at baseline and at 3- and 6-year follow-ups as walking speed, the Short Physical Performance Battery (SPPB), and self-reported mobility disability (ability to walk 400 m or climb one flight of stairs). Both long (>= 9 h) TST and long TIB predicted accelerated decline in objectively measured physical performance and greater incidence in subjectively assessed mobility disability, but short (<= 6 h) TST did not. After combining TST and TIB, long sleepers (TST and TIB >= 9 h) experienced the greatest decline in physical performance and had the highest risk for incident mobility disability in comparison to mid-range sleepers with 7-8 h TST and TIB. Subjective short sleepers reporting short (<= 6 h) TST but long (>= 9 h) TIB showed a greater decline in SPPB score and had a higher risk of incident mobility disability than true short sleepers with short (<= 6 h) TST and TIB <= 8 hours. Conclusions: Extended time in bed as well as long total sleeping time is associated with greater physical function decline than mid-range or short sleep. TIB offers important additive information to the self-reported sleep duration when evaluating the consequences of sleep duration on health and functional status.