Table 1.

Characteristics of 19,567 Chinese adults according to frequency of napping, the Guangzhou Biobank Cohort Study, 2003-2006

	Frequency of napping
	Never	1-3 days/week	4-6 days/week	Daily	P value*
n	6,415	2,833	2,512	7,807
Sex
Men	20.6	23.7	29.5	36.6
Women	79.4	76.3	70.5	63.4	< 0.001
Age (year)	61.4 ± 6.8	61.2 ± 6.6	62.8 ± 6.4	63.0 ± 6.6	< 0.001
Education					< 0.001
Primary or below	49.8	43.4	43.8	42.9
Secondary	43.7	47.6	45.7	45.8
Tertiary	6.5	9.1	10.5	11.3
Occupation					0.67
Manual	70.9	68.9	69.6	68.1
Non-manual (office setting)	12.4	14.9	16.7	17.2
Non-manual (other setting)	9.5	8.9	9.2	8.9
Other	7.3	7.2	4.5	5.8
Ever smoked	20.4	21.9	24.1	28.8	0.009
Ever consumed alcohol	15.5	18.1	17.8	20.9	0.20
Physical activity level†					0.013
Inactive	10.3	9.5	5.3	7.3
Minimally active	48.8	48.3	41.7	48.9
Active	41.0	42.2	53.0	43.9
Health status
Poor self-rated health status	15.0	16.8	14.2	17.0	0.014
Hospital admission in last 6 months	3.0	3.2	2.9	4.5	0.12
Hypertension	41.9	42.7	47.5	48.4	< 0.001
Cardiovascular conditions	4.6	4.3	5.7	6.4	0.17
Familial history of diabetes	9.1	10.4	9.3	8.9	0.26
Adiposity and metabolic markers
Waist circumference (cm)	78.7 ± 8.8	78.7 ± 8.9	79.9 ± 8.9	79.6 ± 8.9	0.10
Systolic blood pressure (mm Hg)	130 ± 22	130 ± 22	133 ± 22	132 ± 22	0.001
Fasting glucose (mmol/L)	5.7 ± 1.6	5.7 ± 1.7	5.9 ± 1.7	5.9 ± 1.8	< 0.001
Triglycerides (mmol/L)	1.6 ± 1.2	1.6 ± 1.3	1.61 ± 1.1	1.7 ± 1.3	< 0.001
Total cholesterol (mmol/L)	6.0 ± 1.2	6.0 ± 1.2	5.8 ± 1.1	5.9 ± 1.2	0.44
Sleep variables
Total sleep duration (hour)	6.6 ± 1.2	6.9 ± 1.3	6.9 ± 1.2	7.2 ± 1.4	< 0.001
Insomnia	15.8	14.7	13.4	14.1	0.46
Daytime sleepiness	5.5	5.1	2.8	2.5	< 0.001
Snoring	38.7	42.9	50.4	43.6	0.63

Data are means ± SD or percentages.

^*P value for linear trend was adjusted for age

^†Physical activity was quantified using the short version of the International Physical Activity Questionnaire (IPAQ)