Table 2. Subgroup meta-analyses of cross-sectional studies to explore sources of heterogeneity.

Subgroups	Short sleep		Long sleep
	No.of studies	OR (95% CI) P for heterogeneity	No. of studies	OR (95% CI) P for heterogeneity
Gender
Men	3	1.27 (1.08, 1.49)	3	1.03 (0.80, 1.33)
Women	3	1.49 (1.29, 1.72)	3	0.94 (0.80, 1.12)
		P=0.156		P=0.588
Mean age (years)
aMiddle	5	1.34 (1.21, 1.48)	4	1.15 (1.04, 1.28)
bElderly	2	0.96 (0.86, 1.06)	2	1.03 (0.90, 1.18)
		P<0.1		P=0.210
Location
Asia	6	1.18 (1.11, 1.26)	6	1.08 (1.01, 1.16)
Europe	2	1.09 (0.74, 1.61)	2	1.81 (1.30, 2.52)
USA	4	1.40 (1.15, 1.72)	3	1.18 (0.89, 1.56)
		P=0.237		P<0.1
Cohorts-based
Community	6	1.15 (1.07, 1.23)	6	1.12 (1.03, 1.21)
Hospital	3	1.33 (1.18, 1.49)	3	1.01 (0.86, 1.18)
		P<0.1		P=0.263
Measure of sleeping
Interview	3	1.14 (1.06, 1.23)	3	1.09 (1.00, 1.19)
Questionnaire	9	1.29 (1.18, 1.42)	8	1.16 (1.03, 1.31)
		P<0.1		P<0.1
Metabolic syndrome
NCEP ATP-III	4	1.48 (1.30, 1.68)	4	0.93 (0.80, 1.07)
Modified NCEP ATP-III	4	1.02 (0.94, 1.11)	4	1.24 (1.13, 1.36)
AHA-NHLBI	2	1.36 (1.10, 1.67)	2	1.15 (0.86, 1.54)
Modified AHA-NHLBI	1	2.30 (0.71, 7.50)	1	1.89 (0.51, 7.00)
JASSO	1	1.39 (1.21, 1.60)	1	0.98 (0.83, 1.16)
		P<0.1		P<0.1
Quality of study
High	7	1.06 (0.99, 1.15)	6	1.23 (1.13, 1.34)
Low	5	1.44 (1.31, 1.58)	5	0.96 (0.86, 1.07)
		P<0.1		P<0.1

Abbrevations: AHA-NHLBI, American Heart Association/National Heart Lung and Blood Institute; CI, confidence interval; JASSO, Japan Society for the Study of Obesity; NCEP ATP-III, National Cholesterol Education Adult Treatment Panel III; OR, odds ratios.

^aMiddle, <60 or ⩽61.

^bElderly, >60 or ⩾61.