Table 5 Association between sleep duration and dementia: analysis restricted to participants without mental disorders before 65 years.

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

  Total population Among those free of mental disorders before 65 years
N cases/N total HRa (95% CI) P valueb N cases/N total HRa (95% CI) P valueb
Sleep duration at age 50
 Short: ≤6 h 211/3149 1.22 (1.01–1.48) 0.04 195/2890 1.25 (1.03–1.53) 0.03
 Normal: 7 h 219/3624 1 (ref.)   202/3393 1 (ref.)  
 Long: ≥8 h 91/1186 1.25 (0.98–1.60) 0.07 82/1093 1.23 (0.95–1.60) 0.11
Sleep duration at age 60
 Short: ≤6 h 192/2759 1.37 (1.10–1.72) 0.005 170/2520 1.28 (1.02–1.62) 0.04
 Normal: 7 h 142/2988 1 (ref.)   134/2779 1 (ref.)  
 Long: ≥8 h 75/1417 1.15 (0.87–1.52) 0.34 72/1288 1.20 (0.90–1.60) 0.22
Sleep duration at age 70
 Short: ≤6 h 171/2429 1.24 (0.98–1.57) 0.10 159/2237 1.28 (1.00–1.63) 0.049
 Normal: 7 h 131/2578 1 (ref.)   122/2418 1 (ref.)  
 Long: ≥8 h 90/1509 1.15 (0.88–1.51) 0.60 85/1391 1.22 (0.93–1.62) 0.16
Trajectories of sleep duration between age 50 and 70
 Persistent short 103/1358 1.30 (1.00–1.69) 0.048 94/1253 1.29 (0.98–1.69) 0.06
 Persistent normal 141/2520 1 (ref.)   132/2353 1 (ref.)  
 Persistent long 35/461 1.28 (0.88–1.85) 0.20 32/430 1.26 (0.85–1.85) 0.25
 Change from short to normal 61/1086 1.20 (0.89–1.63) 0.23 59/1006 1.28 (0.94–1.74) 0.12
 Change from normal to long 47/946 1.02 (0.73–1.42) 0.90 45/870 1.11 (0.79–1.56) 0.55
 Change from normal to short 39/504 1.13 (0.79–1.62) 0.50 36/462 1.16 (0.80–1.56) 0.43
  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, alcohol consumption, physical activity, smoking status, and fruit and vegetable consumption, BMI, hypertension, diabetes, cardiovascular disease, GHQ depression, and CNS medications.
  3. bTwo-sided P value for HR in comparison with the reference (ref.) category, without adjustment for multiple comparisons.