Table 5.

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

	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

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, alcohol consumption, physical activity, smoking status, and fruit and vegetable consumption, BMI, hypertension, diabetes, cardiovascular disease, GHQ depression, and CNS medications.

^bTwo-sided P value for HR in comparison with the reference (ref.) category, without adjustment for multiple comparisons.