Abstract
INTRODUCTION: The joint association of night-time sleep duration and daytime napping (siesta) with mortality remains elusive. We explored sleep patterns and long-term mortality in older adults and tested whether the relationship is modified by cognitive function. METHODS: We analysed data from 1519 participants in the National Health and Nutrition Survey of older adults aged 65+ years ('Mabat Zahav'), conducted by the Israel Center for Disease Control during 2005-2006. A detailed questionnaire was administered at study entry to gather information on sleeping habits, including night-time sleep duration and siesta. A Mini-Mental State Examination was administered to assess cognitive status (score <27 considered impaired). Mortality data were obtained from the Ministry of Health (last follow-up: June 2019; 782 deaths). Cox models were constructed to estimate the HRs for mortality associated with sleep patterns, defined according to night sleep duration (>8 vs ≤8 hours) and siesta (Y/N). Spline regression models were constructed to examine the linearity of the association across cognitive statuses. RESULTS: Sleep categories among participants (mean age 75; 53% women) included 291 (19.2%) with long night sleep and siesta, 139 (9.1%) with long night sleep and no siesta, 806 (53.1%) with short night sleep and siesta, and 283 (18.6%) with short night sleep and no siesta. HRs for mortality were 2.07 (95% CI: 1.63 to 2.62), 1.63 (95% CI: 1.22 to 2.18) and 1.43 (95% CI: 1.16 to 1.76) in the former three versus latter sleep patterns, respectively. Multivariable adjustment for sociodemographic, behavioural and clinical covariates attenuated the HRs to 1.27-1.41 (all p<0.05). The relationship between night sleep duration and mortality was linear (p(linearity)=0.047) among cognitively preserved individuals and U-shaped (p(non-linearity)<0.001) among cognitively impaired ones. CONCLUSIONS: Prolonged night sleep and siesta were associated with increased mortality, a relationship that varied by cognitive performance.