Table 2 Association between sleep duration at 50, 60, and 70 years and incidence of dementia.

From: Association of sleep duration in middle and old age with incidence of dementia

  N cases/N total Incidence rate per 1000 persons-years Model 1: adjusted for sociodemographic variablesa Model 1 + behavioural factorsb Model 1 + health-related factorsc Fully adjusted model
HR (95%CI) P valued HR (95%CI) P valued HR (95%CI) P valued HR (95%CI) P valued
Sleep duration at age 50e 521/7959          
 Short: ≤6 h 211/3149 2.8 (2.4–3.2) 1.28 (1.06–1.55) 0.01 1.27 (1.05–1.54) 0.01 1.22 (1.01–1.48) 0.04 1.22 (1.01–1.48) 0.04
 Normal: 7 h 219/3624 2.4 (2.1–2.7) 1 (ref.)   1 (ref.)   1 (ref.)   1 (ref.)  
 Long: ≥8 h 91/1186 3.0 (2.4–3.7) 1.25 (0.98–1.59) 0.08 1.25 (0.98–1.60) 0.07 1.24 (0.97–1.59) 0.09 1.25 (0.98–1.60) 0.07
Sleep duration at age 60e 409/7164          
 Short: ≤6 h 192/2759 4.7 (4.0–5.4) 1.48 (1.19–1.84) <0.001 1.46 (1.17–1.82) 0.001 1.38 (1.11–1.73) 0.004 1.37 (1.10–1.72) 0.005
 Normal: 7 h 142/2988 3.2 (2.7–3.7) 1 (ref.)   1 (ref.)   1 (ref.)   1 (ref.)  
 Long: ≥8 h 75/1417 3.6 (2.8–4.4) 1.15 (0.87–1.52) 0.33 1.17 (0.88–1.55) 0.28 1.13 (0.85–1.50) 0.39 1.15 (0.87–1.52) 0.34
Sleep duration at age 70e 392/6516          
 Short: ≤6 h 171/2429 9.3 (7.9–10.7) 1.33 (1.06–1.68) 0.004 1.29 (1.03–1.63) 0.005 1.26 (1.00–1.60) 0.04 1.24 (0.98–1.57) 0.10
 Normal: 7 h 131/2578 6.8 (5.6–7.9) 1 (ref.)   1 (ref.)   1 (ref.)   1 (ref.)  
 Long: ≥8 h 90/1509 8.1 (6.4–9.7) 1.22 (0.94–1.60) 0.39 1.13 (0.91–1.55) 0.34 1.18 (0.90–1.55) 0.22 1.15 (0.88–1.51) 0.60
  1. CI confidence intervals, HR hazard ratio, SD standard deviation.
  2. aHR estimated from a Cox regression adjusted for age (timescale), sex, ethnicity, education, and marital status.
  3. bAdditionally adjusted for alcohol consumption, physical activity, smoking status, and fruit and vegetable consumption.
  4. cAdditionally adjusted for BMI, hypertension, diabetes, cardiovascular disease, GHQ depression, and CNS medications.
  5. dTwo-sided P value for HR in comparison with the reference (ref.) category, without adjustment for multiple comparisons.
  6. eFollow-up: at age 50, mean = 24.6 years, SD = 7.0 years, range = 0.18–33.6 years; at age 60, mean = 14.8 years, SD = 5.9 years, range = 0.11–33.6 years; at age 70, mean = 7.5 years, SD = 4.7 years, range = 0.04–21.8 years.