Changes in nocturnal sleep and daytime nap durations predict all-cause mortality among older adults: the Panel on Health and Ageing of Singaporean Elderly.

Study Objectives: To determine the effects of changes in nocturnal sleep and daytime nap durations on all-cause mortality among older adults.
Methods: Two-thousand four-hundred forty-eight community-dwelling older Singaporeans (≥60 years) reported their nocturnal sleep and daytime nap durations at baseline (2009) and the 2-year follow-up. At each phase, they were grouped into the recommended (7-8 hours), short (≤6 hours), and long (≥9 hours) sleep duration categories, and the none (0 hour), short (≤1 hour), and long (>1 hour) nap duration categories. Cox regression analysis was conducted to quantify the associations of changes in sleep and nap durations over 2 years with all-cause mortality risk in the subsequent 4 years (till end of 2015). Multivariable fractional polynomial regression, which treated sleep and nap durations as continuous variables was conducted as a supplementary analysis.
Results: Relative to individuals who had the recommended sleep durations at both baseline and follow-up, the risks of all-cause mortality were higher among older adults who reported considerable changes in sleep duration (from short to long sleep and vice versa, hazard ratio [HR] = 2.14-2.56). Furthermore, compared to those who did not nap at both time points, significantly higher mortality risks were found in individuals who showed any increase in nap duration (HR = 1.86-2.16), or reduced their nap from long to short duration (HR = 1.86). Supplementary analysis revealed similar findings.
Conclusions: In addition to the change in nocturnal sleep duration, change in daytime nap duration can also predict risks of all-cause mortality among older adults. It is crucial to track older adults' sleep and nap durations longitudinally.