Degraded Circadian Regulation Predicts Incident Physical Disability And All-Cause Mortality In Community-Based Older Adults

Circadian/sleep disturbances are common in people with physical disability that is linked to mortality. We tested whether circadian disturbances predict incident physical disability and mortality in community-based older adults. We studied 1,256 older adults (age: 81.2±7.4 [SD]) in the Rush Memory and Aging Project who have been followed for up to 13 years. Motor activities of up to 10 days were recorded at baseline and were used to quantify the interdaily stability (IS) and intradaily variability (IV) of the circadian activity rhythm. Disability was assessed annually using three tests for basic activities of daily living (ADL; using the Katz scale), instrumental activities of daily living (IADL; adapted from the Duke Older Americans Resources and Services project), and mobility disability (using the Rosow-Breslau scale), respectively. Cox proportional hazards models were performed to examine the associations of IS and IV with incident physical disability and separately with all-cause death while adjusted for age, sex, and education. Of 1,047 participants without ADL disability at baseline, 514 developed ADL disability in 4.2±2.8 years. Of 625 participants without IADL disability, 431 developed IADL disability in 3.0±2.3 years. Of 665 participants without mobility disability, 429 developed mobility disabilities in 3.2±2.3 years. Of all 1,256 participants, 519 died in 5.7±2.9 years after baseline. For 1-SD decrease in IS (0.13), the risk of disability increased by 24% in ADL (95%CI: 0.13-0.36, p<0.0001) and the risk of all-cause death increased by 12% (95%CI: 0.02-0.22, p=0.01). We did not observe an association of IS with incident IADL or mobility (both p’s>0.5). For 1-SD increase in IV (0.20), the disability risk in ADL, IADL, mobility, and the death risk increased respectively by 34% (95%CI: 0.23-0.46, p<0.0001), 14% (95%CI: 0.05-0.26, p=0.005), 17% (95%CI: 0.06-0.28, p=0.002), and 32% (95%CI: 0.23-0.42, p<0.0001). Old subjects with less stable or more fragmented daily activity rhythms had increased risk for developing physical disability and all-cause death. This work was supported by NIH grants R01AG048108, RF1AG059867, R01AG017917, and R01NS078009.