Table I.

Characteristics of included studies

Study	Country	No. of samples	Gender (male,%)	Age, mean [years]	BMI, mean [kg/m2]	Study design	Diagnostic method of OSA	OSA category (AHI or RDI)	Nocturnal IH category (ODI or CT90)	MS criteria
Coughlin et al. 2004	UK	104	All were male	49.6	33.5	Hospital-based Cross-sectional	Standard PSG	OSA ≥ 15 Non-OSA ≤ 15	N/A	NCEP ATPIII
Sasanabe et al. (male) 2006	Japan	778	All were male	47.9	27.4	Hospital-based Cross-sectional	Standard PSG	OSA ≥ 15 Non-OSA ≤ 5	N/A	Japanese criteria
Sasanabe et al. (female) 2006	Japan	130	All were female	51.9	26.9	Hospital-based Cross-sectional	Standard PSG	OSA ≥ 15 Non-OSA ≤ 5	N/A	Japanese criteria
Gruber et al. 2006	UK	79	N/A	47.3	33.3	Hospital-based Cross-sectional	Standard PSG	OSA ≥ 5 Non-OSA ≤ 5	N/A	IDF guidelines
Nieto et al. 2009	USA	546	56	59.9	31.1	Population-based Cross-sectional	Standard PSG	OSA ≥ 15 or CPAP Non-OSA ≤ 5	N/A	NCEP ATPIII
Chin et al. 2010	Japan	275	All were male	44	23.9	Population-based Cross-sectional	Portable PSG	OSA ≥ 5 Non-OSA ≤ 5	N/A	NCEP ATPIII
Muraki et al. (male) 2010	Japan	1710	All were male	58	24	Population-based Cross-sectional	Pulse-oximetry	N/A	ODI ≥ 5 vs. ODI < 5	NCEP ATPIII
Muraki et al. (female) 2010	Japan	2896	All were female	56.5	23.3	Population-based Cross-sectional	Pulse-oximetry	N/A	ODI ≥ 5 vs. ODI < 5	NCEP ATPIII
Troxel et al. 2010	USA	290	N/A	N/A	N/A	Population-based Case-control	Portable PSG	As continuous variable	N/A	NCEP ATPIII
Theorell et al. 2011	Sweden	400	All were female	50.1	26.7	Population-based Cross-sectional	Standard PSG	As continuous variable	ODI and CT90 as continuous variables	NCEP ATPIII
Gasa et al. 2011	Spain	159	44.5	43	46.1	Hospital-based Cross-sectional	Standard PSG	OSA ≥ 15Non-OSA ≤ 15	CT90 ≥ 4.65% of TST vs. CT90 < 4.65% of TST	NCEP ATPIII
Agrawal et al. 2012	India	227	78.4	45.2	32	Hospital-based Case-control	Standard PSG	N/A	CT90 as continuous variable	NCEP ATPIII
Hall et al. 2012	USA	340	All were female	51.2	29.8	Population-based Case-control	Standard PSG	As continuous variable	N/A	NCEP ATPIII

OSA – obstructive sleep apnea, MS – metabolic syndrome, PSG – polysomnography, AHI – apnea hypopnea index, RDI – respiratory disturbance index, IH – intermittent hypoxia, ODI – oxygen desaturation index, CT90 – cumulative percentage of sleep time with SpO₂ below 90%, TST – total sleep time, NCEP ATPIII – National Cholesterol Education Program Adult Treatment Panel III, IDF – International Diabetes Federation, N/A – not available.