Table 2.
Association between sleep duration at 50, 60, and 70 years and 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 |
CI confidence intervals, HR hazard ratio, SD standard deviation.
aHR estimated from a Cox regression adjusted for age (timescale), sex, ethnicity, education, and marital status.
bAdditionally adjusted for alcohol consumption, physical activity, smoking status, and fruit and vegetable consumption.
cAdditionally adjusted for BMI, hypertension, diabetes, cardiovascular disease, GHQ depression, and CNS medications.
dTwo-sided P value for HR in comparison with the reference (ref.) category, without adjustment for multiple comparisons.
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.