Table 2.

Ten years examining the relationship between sleep duration and type 2 diabetes mellitus.

Study	Number of studies	Number of participants	Age	Sleep recordings	Sleep duration	Comparator	Range of follow-up (years)	Diagnosis of T2DM	Outcome	95% CI	I2	Adjustment for covariates
Cappuccio et al. 2010	9	93,702	≥19	Self-reported	Short sleep (<7 h)	Normal (7 h)	4.2–32	Self-reported, blood test	Τ2DM: RR = 1.28	1.03, 1.60	58	1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 19
Cappuccio et al. 2010	7	91,514	≥19	Self-reported	Long sleep (>8 h)	Normal (7 h)	4.2–32	Self-reported, blood test	T2DM: RR = 1.48	1.13, 1.96	37
Holliday et al. 2013	10	447,124	N/A	N/A	Short sleep (<6 h)	Normal (7 h)	2–17	N/A	T2DM: HR = 1.33	1.20, 1.48	32	1, 2, 3, 4, 5, 6, 8, 13
Shan et al. 2015	9	395,584	≥32	Self-reported	Short sleep (<6 h)	Normal (7 h)	2.5–16	Medical records, self-reported, blood test	T2DM: RR = 1.06	1.01, 1.11	7.5	1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17
Shan et al. 2015	9	395,584	≥32	Self-reported	Short sleep (≤5 h)	Normal (7 h)	2.5–16	Medical records, self-reported, Blood test	T2DM: RR = 1.37	1.18, 1.59	57.1
Shan et al. 2015	7	244,507	≥19	Self-reported	Long sleep (8 h)	Normal (7 h)	2.5–16	Medical records, self-reported, blood test	T2DM: RR = 1.11	0.97, 1.28	59
Shan et al. 2015	7	244,507	≥19	Self-reported	Long sleep (≥9 h)	Normal (7 h)	2.5–16	Medical records, self-reported, blood test	T2DM: RR = 1.40	1.08, 1.80	75.8
Anothaisintawee et al. 2016	14	583,263	≥18	Self-reported	Short sleep (≤5 h)	Normal (7–8 h)	2–32	Medical records, self-reported, blood test	T2DM: RR = 1.48	1.25, 1.76	N/A	1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 13, 14, 16, 18
Anothaisintawee et al. 2016	10	Ν/Α	≥18	Self-reported	Short sleep (<6 h)	Normal (7–8 h)	2–32	Medical records, self-reported, blood test	T2DM: RR = 1.18	1.10, 1.26	N/A
Anothaisintawee et al. 2016	13	Ν/Α	≥18	Self-reported	Long sleep (≥9 h)	Normal (7–8 h)	2–32	Medical records, self-reported, blood test	T2DM: RR = 1.36	1.12, 1.5	N/A
Itani et al. 2017	18	322,842	≥18	Self-reported, objectively	Short sleep (<7 h)	Normal (7–8 h)	1–30	Self-reported, blood test	T2DM: RR = 1.37	1.22, 1.53	53	1, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23
Jike et al. 2018	16	318,437	≥18	Self-reported, objectively	Long sleep (>7 h)	Normal (6–8 h)	1–34	Self-reported, blood test	T2DM: RR = 1.26	1.11, 1.43	63

Adjustment for covariates: (1) age, (2) sex, (3) BMI or other measure of weight/adiposity, (4) physical activity, (5) smoking, (6) alcohol consumption, (7) comorbidities (hypertension, dyslipidaemia), (8) socioeconomic factors (income, health insurance status, employment status, education, marital status), (9) family history of diabetes, (10) depression and other mental diseases, (11) sleep-related disorders, (12) race/ethnicity, environmental factors (residence), (13) baseline health status, (14) caffeine consumption, (15) glucose levels, (16) occupational factors (shift work, working hours, occupational stress), (17) postmenopausal hormone use, (18) metabolic rate, (19) study or institution level, (20) insulin sensitivity, (21) napping, (22) total calorie intake, (23) dietary habits.

HbA1c, haemoglobin A1c; I², heterogeneity; N/A, not available; RR, relative risk; T2DM, type 2 diabetes mellitus.