• Jun Miyata, Isao Muraki, Hiroyasu Iso, Kazumasa Yamagishi, Nobufumi Yasuda, Norie Sawada, Manami Inoue, Shoichiro Tsugane, and JPHC Disabling Dementia Study Group.
• Department of Island and Community Medicine, Nagasaki University Graduate School of Biomedical Sciences, 205 Yoshikugicho, Goto, Nagasaki 853-8691, Japan; Public Health, Department of Social Medicine, Osaka University Graduate School of Medicine, 2-2 Yamadaoka, Suita, Osaka 565-0871, Japan.
• Prev Med. 2024 Mar 1; 180: 107884107884.

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.Copyright © 2024. Published by Elsevier Inc.

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