Table 2.

Associations of 7-day variability in sleep duration and sleep onset timing with risk of total cardiovascular disease

	Cases/Person-years	Model 1	Model 2 HR (95% CI)	Model 3
SD of sleep duration
Categorical
≤60 min	29/3,278	1.00 (ref)	1.00 (ref)	1.00 (ref)
61–90 min	23/2,541	1.06 (0.61, 1.85)	1.07 (0.61, 1.88)	1.09 (0.62, 1.92)
91–120 min	26/1,842	1.61 (0.93, 2.76)	1.54 (0.89, 2.65)	1.59 (0.91, 2.76)
>120 min	33/1,711	2.18 (1.31, 3.63)	2.02 (1.20, 3.39)	2.14 (1.24, 3.68)
Continuous
Per 1 hour	111/9,372	1.41 (1.12, 1.79)	1.36 (1.07, 1.73)	1.39 (1.08, 1.78)
P-trend		0.006	0.02	0.002
Binary
≤90 min	52/5,818	1.00 (ref)	1.00 (ref)	1.00 (ref)
>90 min	59/3,554	1.83 (1.25, 2.68)	1.72 (1.17, 2.53)	1.76 (1.18, 2.63)
P-value		0.004	0.01	0.009
SD of sleep onset timing
Categorical
≤30 min	17/1,846	1.00 (ref)	1.00 (ref)	1.00 (ref)
31–60 min	31/3,235	1.19 (0.66, 2.16)	1.21 (0.66, 2.22)	1.16 (0.64, 2.13)
61–90 min	25/2,022	1.51 (0.81, 2.82)	1.48 (0.79, 2.78)	1.52 (0.81, 2.88)
>90 min	38/2,269	2.05 (1.14, 3.69)	1.95 (1.08, 3.54)	2.11 (1.13, 3.91)
Continuous
Per 1 hour	111/9,372	1.17 (1.06, 1.30)	1.16 (1.05, 1.29)	1.18 (1.06, 1.31)
P-trend		0.002	0.005	0.002
Binary
≤90 min	73/7,103	1.00 (ref)	1.00 (ref)	1.00 (ref)
>90 min	38/2,269	1.67 (1.12, 2.48)	1.58 (1.05, 2.37)	1.69 (1.10, 2.61)
P-value		0.01	0.03	0.02

Model 1: Stratified by study site, and adjusted for age, sex, race/ethnicity, education and work schedules Model 2: Model 1 + adjusted for smoking status, physical activity, depressive symptoms, BMI, diabetes status, systolic blood pressure, HDL cholesterol and total cholesterol

Model 3: Model 2 + adjusted for average sleep duration, insomnia symptom scores, chronotype, Epworth Sleepiness Scale and AHI

AHI = Apnea-Hypopnea Index; BMI = body mass index; CI = confidence interval; HR = hazard ratio; SD = standard deviation