Table 1.

The characteristics and outcomes of included studies

Reference	Study location	Follow-up, years	Sex	Sample size/ Incident T2DM	Adjustment factors	Exposure and effect size (95% CI)
Lin et al.,2017 [13]	Taiwan	13	M&F	32,697/1231	age, income, sex, co-morbidities (hypertension, mental disorders, ischemic heart disease, stroke, heart failure, dementia, hyperlipidemia, anemia, Parkinson’s disease, atrial fibrillation, liver cirrhosis, peripheral vascular disease, renal dialysis), anticoagulants, anti-platelet agents, lipid-lowering agents	COPD VS No COPD:1.09 (1.02–1.17) COPDea VS No COPD: 2.18 (1.88–2.52)
Lee et al.,2013 [14]	Taiwan	5.5	M&F	16,088/884	age, sex, residential area, socioeconomic status, steroid use, hypertriglyceridemia, hypertension, coronary artery disease and cerebrovascular disease	COPD VS No COPD: 1.41 (1.23–1.63)
Sode et al.,2011 [15]	Denmark	27	M&F	7,419,791/292228	age, sex, descent, geographical residency, and level of education	COPD VS No COPD: 1.21 (1.20–1.23)
Song et al.,2010 [16]	U.S	12.2	F	34,056/2016	age, randomized treatment assignment, BMI, physical activity, smoking, alcohol intake, postmenopausal hormone use, family history of diabetes, history of hypertension, history of hypercholesterolemia, total calorie intake, dietary factors	COPD VS No COPD:1.33 (1.09–1.63)
Rana et al.,2004 [17]	U.S	8	F	97,245/2959	age, BMI, sedentary, smoking status, daily alcohol intake, a dietary score variable	COPD VS No COPD: 1.80 (1.10–2.80)
Ford et al.,2004 [18]	U.S	22	M&F	6555/519	age, sex, race, ethnicity, education, smoking status, systolic blood pressure, use of antihypertensive medication, cholesterol concentration, BMI, alcohol use, recreational exercise, non-recreational activity	COPD (moderate or severe) VS No COPD: 1.02 (0.68–1.53); COPD (mild) VS No COPD: 0.66 (0.39–1.12)
Zaigham et al.,2016 [4]	Sweden	26	M&F	27,711/4746	age, height, BMI, smoking status, ESR (log transformed), baseline glucose, cholesterol, physical activity, antihypertensive medication, social class, family history of diabetes, alcohol abuse.	FEV1% in males:≥106.34, 1.0 (reference); 95.57–106.34, 1.06 (0.97–1.17);84.65–95.57, 1.12 (0.95 to 1.33); ≤84.65, 1.48 (1.35–1.63); FEV1% in females:≥106.67, 1.0 (reference); 96.13–106.67, 1.26 (1.04–1.53); 85.14–96.12, 1.26 (1.04–1.53); ≤85.13, 1.45 (1.20–1.75); FVC% in males:≥106.88, 1.0 (reference); 97.42–106.88, 1.06 (0.96–1.17); 87.34–97.42, 1.24 (1.13–1.37); ≤87.34, 1.48 (1.35–1.63); FVC% in females:≥107.50, 1.0 (reference); 97.33–107.49, 1.03 (0.85–1.24); 87.95–97.30, 1.31 (1.09–1.58); ≤87.94, 1.39 (1.16–1.67); FEV1/FVC in males < 70% VS ≥70%:1.06 (0.98–1.16); FEV1/FVC in females < 70% VS ≥70%:0.99 (0.81–1.22)
Oda, E et al.,2016 [5]	Japan	6	M&F	2967/89	age, sex, BMI, current smoking and use of antihypertensive drugs, HbA1c, log hs-CRP	FVC%: 102.00–139.00, 1.0 (reference); 92.00–101.00, 1.05 (0.55–1.99); 54.00–91.00, 1.69 (0.95–3.01); FEV1/FVC: 84.00–99.00, 1.0 (reference); 79 .00–83.00, 1.03 (0.57–1.86);37.00–78.00, 1.67 (0.89–3.12)
Kim et al.,2014 [6]	Korea	4.7	M&F	16,195/640	age, sex, exercise, drinking, smoking habits, hypertension, BMI, waist circumference, fasting glucose level.	FEV1%: 85.80–103.20, 1.0 (reference); 70.70–84.30, 1.12 (0.86–1.47); 65.10–84.10, 1.07 (0.73–1.58); FVC%:84.80–101.20, 1.0 (reference); 75.30–95.10, 1.07 (0.73–1.58); 69.40–79.00, 1.12 (0.86–1.47); FEV1/FVC: 78.00–88.00, 1.0 (reference); 62.00–76.00, 1.12 (0.86–1.47)
Kwon et al.,2012 [7]	Korea	5	M	9220/207	age, BMI, education, smoking, exercise, alcohol, HOMA-IR, cholesterol, triglycerides, and high-density lipoprotein cholesterol	FEV1%: > 119.90, 1.0 (reference); 105.50–119.90,1.08 (0.69–1.70); 94.60–105.50, 1.46 (0.95–2.25);≤94.60,1.58 (1.04–2.39); FVC%:≥109.10, 1.0 (reference); 98.60–109.10, 1.66 (1.05–2.62); 89.40–98.60, 1.11 (0.69–1.80);≤89.40,1.84 (1.19–2.84)
Heianza et al.,2012 [8]	Japan	4	M	5346/214	age, parental history of diabetes, physical activity, smoking status, BMI, hypertension, log-transformed triglycerides, high-density lipoprotein cholesterol, HbA1c	FEV1%:≥104.10, 1.0 (reference); 96.40–104.00, 1.25 (0.79–1.99); 88.80–96.30, 1.76 (1.15–2.69);≤88.70, 1.73 (1.14–2.62); FVC%:≥111.70, 1.0 (reference); 103.90–111.60, 1.03 (0.67–1.58); 95.8–103.8, 1.17 (0.77–1.76);≤95.70,1.39 (0.95–2.05); FEV1/FVC:≥83.10, 1.0 (reference); 80.00–83.00, 1.11 (0.75–1.65); 75.90–79.90, 1.10 (0.74–1.63);≤75.80, 0.98 (0.64–1.50)
Wannamethee et al.,2010 [9]	U.K	20	M	4434/256	age, BMI, smoking, physical activity, alcohol intake, social class, evidence of CHD (undiagnosed),triglycerides, SBP, high-density lipoprotein cholesterol, blood glucose, GGT,CRP, IL-6	FEV1: Highest, 1.0 (reference); Lowest, 1.67 (1.09–2.56); FVC: Highest, 1.0 (reference); Lowest, 1.46 (0.97–2.20); FEV1/FVC:≥82.00, 1.0 (reference); 77.00–82.00, 0.77 (0.55–1.07); 71.00–77.00, 0.87 (0.63–1.21);≤71.00, 0.67 (0.46–0.96)
Yeh et al.,2005 [10]	U.S	9	M&F	11,479/1346	age, race, pack-years of smoking, waist circumference, sport activity index,(FVC% + fasting glucose, HOMA-IR, SBP)	FEV1% in males: Highest, 1.0 (reference); Lowest, 1.70 (1.30–2.10);FEV1% in females: Highest, 1.0 (reference); Lowest, 1.50 (1.10–1.90);FVC% in males: > 108.40, 1.0 (reference); <  90.8, 1.30 (1.00–1.70);FVC% in females: > 114.60, 1.0 (reference); <  95.70, 1.40 (1.10–1.80)

^a The study by Lin et al. reported the results of COPD patients with and without exacerbations. BMI Body Mass Index, CHD coronary heart disease, CI confidence interval, CRP C-reactive protein, COPD chronic obstructive pulmonary disease, COPDe COPD patients with exacerbations, ESR erythrocyte sedimentation rate, F female, FEV1 forced expiratory volume in 1 s, FVC forced vital capacity, GGT gamma-glutamyl transpeptidase, HbA1c glycosylated hemoglobin, HDL high density lipoprotein, HOMA-IR homeostasis model assessment of insulin resistance, IL-6 interleukin-6, M male, SBP systolic blood pressure, T2DM type 2 diabetes mellitus, U.K United Kingdom, U.S United States