Sleep duration, its change, and risk of dementia among Japanese: The Japan Public Health Center-based Prospective Study

Abstract

ObjectivePrevious findings on the association between sleep duration, changes in sleep duration, and long-term dementia risk were mixed. Thus, we aimed to investigate the association between midlife sleep duration, its change, and dementia. MethodsWe recruited 41,731 Japanese (40–71 years) and documented their habitual sleep duration at baseline (1990–1994) and a 5-year follow-up survey. Changes in sleep duration were calculated as differences between baseline and 5-year measurements. We identified dementia using the Long-Term Care Insurance system (2007–2016). Hazard ratios (HRs) and 95% confidence intervals (CIs) of dementia were calculated using the area-stratified Cox model. ResultsDuring 360,389 person-years, 4621 participants exhibited dementia. The multivariable HRs of dementia compared with 7 h of sleep were 1.13 (95% CI: 0.98–1.30) for 3–5 h, 0.93 (0.85–1.02) for 6 h, 1.06 (0.99–1.14) for 8 h, 1.13 (1.01–1.27) for 9 h, and 1.40 (1.21–1.63) for 10–12 h with a J-shaped fashion (p for linear < 0.001 and quadratic < 0.001). For its change, the HRs compared with no change were 1.02 (0.90–1.16) for decreased ≥2 h, 0.95 (0.88–1.03) for decreased 1 h, 1.00 (0.91–1.09) for increased 1 h, and 1.37 (1.20–1.58) for increased ≥2 h. The positive association for decreased sleep duration was observed in individuals with an initial sleep duration of ≤7 h, but not in those with ≥8 h (p for interaction = 0.007). ConclusionsLong and increased sleep duration was associated with a higher risk of dementia.