Table 1.

Main characteristics of the studies included in this meta-analysis of the association between short sleep duration and NAFLD/MAFLD

	Country	Study design	Sample size	Sex, female	Age (years)	Sleep duration category (h)	Measurement of sleep duration	Definition of NAFLD/MAFLD	Measurement of NAFLD/MAFLD	Confounder adjustment	Quality assessment (Newcastle–Ottawa Scale)
Kim et al. 2013 [21]	Korean	Cross-sectional	45,293	42.4%	39.7 ± 5.9	Short = ≤ 5 Reference = > 7	Self-administered questionnaire	Fatty liver detected by ultrasonography in the absence of any known causes of chronic liver disease or alcohol intake ≥ 20 g/day	Liver ultrasound	Age, smoking status, alcohol intake, physical activity, SBP, education level, marital status, presence of job, sleep apnea, loud snoring, and BMI	Selection: 3 Comparability: 2 Outcome: 3
Imaizumi et al. 2015 [28]	Japan	Cross-sectional	2172	66.3%	60.9 ± 12.7	Short = ≤ 6 Reference = 6–7	Self-administered questionnaire	Fatty liver detected by ultrasonography in the absence of other causes of chronic liver disease or alcoholic consumption ≥ 20 g/day	Liver ultrasound	Age, smoking status, no breakfast, snacking, regular exercise, and BMI	Selection: 4 Comparability: 2 Outcome: 3
Miyake et al. 2015 [23]	Japan	Cohort	2429	72.5%	40.4 ± SD*	Short = ≤ 6 Reference = 7–8	Self-administered questionnaire	Fatty liver detected by ultrasonography in the absence of other causes of chronic liver disease or alcoholic misuse	Liver ultrasound	Age, BMI, SBP, TG, HDL-C, FPG, UA, ALT, Cre, snacking habit, and periodic exercise habit	Selection: 4 Comparability: 2 Outcome: 2
Yu et al. 2015 [30]	Korean	Cross-sectional	335	49.9%	54.8 ± SD*	Short = < 5 Reference = ≥ 5	Self-administered questionnaire	Fatty liver detected by abdominal CT in the absence of other causes of chronic liver disease or alcoholic consumption ≥ 140 g/week	Abdominal CT	Age, sex, exercise, alcohol, smoking, DM, HTN, CVD, and BMI	Selection: 2 Comparability: 2 Outcome: 2
Liu et al. 2016 [31]	China	Cohort	8965	56.6%	61.6 ± 7.8	Short = < 6 Reference = 7–8	Self-administered questionnaire	Imaging or histologic evidence of hepatic steatosis, and no other cause for secondary hepatic fat accumulation	Liver ultrasound	Age, sex, education, marriage, smoking, alcohol consumption, physical activity, diabetes, sleep quality, napping, and BMI	Selection: 4 Comparability: 2 Outcome: 3
Peng et al. 2017 [32]	China	Cross-sectional	8559	63.7%	58.5 ± 9.0	Short = ≤ 6 Reference = > 9	Self-administered questionnaire	Fatty liver detected by ultrasonography in the absence of other causes of chronic liver disease or alcoholic consumption ≥ 140 g/week for men or ≥ 70 g/week for women	Liver ultrasound	Age, sex, current smoker, current drinker, physical activity, marital status, habitation status, work status, ALT, HDL-C, LDL-C, TC, HTN, DM, and BMI	Selection: 4 Comparability: 2 Outcome: 3
Kim et al. 2018 [33]	USA	Cross-sectional	17,245	51.3%	45.7 ± SD*	Short = ≤ 5 Reference = ≥ 9	Self-administered questionnaire	NAFLD is defined by US fatty liver index (USFLI) more than 30 in the absence of viral hepatitis or significant alcohol consumption	US fatty liver index	Age, sex, ethnicity, education level, marital status, economic status, BMI, waist circumference, smoking, diabetes, HTN, and TC	Selection: 3 Comparability: 2 Outcome: 2
Kim et al. 2019 [25]	Korean	Cohort	5427	51.8%	50.8 ± SD*	Short = < 6 Reference = 7–8	Self-administered questionnaire	NAFLD is defined by fatty liver index (FLI) more than 60 in the absence of hepatitis history, positive serologic markers for hepatitis B and C or significant alcohol consumption	Fatty liver index	Age, sex, BMI, SBP, DBP, TG, HDL, FDG, physical activity, smoking, daytime napping, and night-time shifting	Selection: 3 Comparability: 2 Outcome: 2
Okamura et al. 2019 [22]	Japan	Cohort	12,306	52.5%	42.0 ± SD*	Short = ≤ 5 Reference = > 7	Self-administered questionnaire	Fatty liver detected by ultrasonography in the absence of viral hepatitis or alcoholic consumption ≥ 140 g/week for men or ≥ 70 g/week for women	Liver ultrasound	Age, BMI, ALT, TG, HDL-C, SBP, exercise habit, alcohol consumption, smoking, and FPG	Selection: 4 Comparability: 2 Outcome: 2
Takahashi et al. 2020 [29]	Japan	Cross-sectional	4828	61.4%	56.2 ± SD*	Short = < 5 Reference = > 7	Self-administered questionnaire	Fatty liver detected by ultrasonography in the absence of viral hepatitis or alcoholic consumption ≥ 30 g/day for men or ≥ 20 g/day for women	Liver ultrasound	Age, smoking habits, physical activity, and BMI	Selection: 3 Comparability: 2 Outcome: 3
Hu et al. 2020 [34]	China	Case–control	1960	72.5%	59.4 ± SD*	Short = < 8 Reference = ≥ 8	Self-administered questionnaire	Fatty liver detected by ultrasonography in the absence of other causes of chronic liver disease or alcoholic consumption ≥ 140 g/week for men or ≥ 70 g/week for women	Liver ultrasound	Age, sex, smoking, drinking, education. Physical activity, work status, SBP, TG, ALT, BMI, bedtime, daytime napping status, sleep quality, and sleep medication use	Selection: 3 Comparability: 2 Outcome: 2
Weng et al. 2021 [35]	USA	Cross-sectional	1786	50.7%	50.0 ± 17.9	Short = < 6 Reference = ≥ 6	Self-administered questionnaire	MAFLD was diagnosed based on the evidence of hepatic steatosis and any of the following three conditions: over weight/obesity, diabetes mellitus, or metabolic dysfunction	Fibroscan	Age, gender, race, diabetes, HTN, waist circumstance, overweight, TG, uric acid, HDL-C, and circadian misalignment	Selection: 4 Comparability: 2 Outcome: 3
Um et al. 2021 [20]	Korean	Cohort	143,306	61.5%	36.6 ± 6.6	Short = ≤ 5 Reference = 7	Self-administered questionnaire	Fatty liver detected by ultrasonography in the absence of other causes of chronic liver disease or alcoholic consumption ≥ 30 g/day for men or ≥ 20 g/day for women	Liver ultrasound	Age, sex, center, year of screening examination, season, alcohol consumption, smoking, physical activity, total energy intake, marital status, education level, depression, diabetes, HTN, BMI, and waist circumference	Selection: 4 Comparability: 2 Outcome: 2
Taheri et al. 2021 [36]	Iran	Case–control	1932	60.9%	49.2 ± 8.8	Short = < 5 Reference = > 7	Self-administered questionnaire	MAFLD was defined as having a fatty liver index (FLI) ≥ 60 plus at least one of the following: being overweight or obese, having a T2DM diagnosis or having any evidence of metabolic dysregulation, and in the absence of other causes of chronic liver disease or alcoholic misuse	Fatty liver index	Age, sex, educational level, marital status, socioeconomic status, and total energy intake	Selection: 3 Comparability: 2 Outcome: 2
Yang et al. 2022 [24]	China	Cross-sectional	5011	60.0%	63.6 ± 10.8	Short = < 7 Reference = 7–8	Self-administered questionnaire	MAFLD was diagnosed based on ultrasound examination of hepatic steatosis and the presence of any one of the following three criteria: overweight/obesity, presence of diabetes mellitus, or evidence of metabolic dysregulation	Liver ultrasound	Age, sex, drinking, smoking, sedentary time, diet diversity, education level, medication, HTN, diabetes, and obesity	Selection: 4 Comparability: 2 Outcome: 3