Characteristics of the included studies and patients with type 2 diabetes
| Ref. | Study author, year | Country (continent) | DM group size (men/women) | Mean age years | Smokers % | BMI kg·m−2 | Fasting blood glucose mmol·L−1 | Glycated Hb % | T2D duration years | Patients with microangiopathy % | Pulmonary function tests | Study quality |
| [9] | Matsubara, 1991 | Japan (As) | 53 (29/23) | 58.0 | NR | NR | NR | 9.5 | 7.4 | NR | FEV1, DLCO | Fair |
| [10] | Lara-Rodríguez, 1995 | Venezuela (Am) | 12 (7/5) | 47.0 | 0 | NR | NR | NR | NR | 83 | FEV1, FVC, FEV1/FVC, FEF25–75%, DLCO | Fair |
| [11] | Barrett-Connor, 1996 | USA (Am) | 139 (71/68) | 75.9 | 5.7 | 26.3 | 6.94 | NR | NR | NR | FEV1, FVC | Good |
| [12] | Katoh, 1996 | Japan (As) | 19 (10/9) | 50.5 | NR | 27.8 | 7.49 | 7.5 | NR | NR | FEV1 | Fair |
| [13] | Isotani, 1999 | Japan (As) | 54 (23/31) | 54.9 | 0 | 22.2 | 9.77 | 9 | 11.0 | 68.5 | FEV1, DLCO | Good |
| [14] | Benbassat, 2001 | Israel (As) | 12 (8/4) | 60 | 0 | 29.6 | NR | 9.0 | 12.8 | 33 | FEV1, FVC, FEF25–75%, DLCO | Good |
| [15] | Zamarrón, 2001 | Spain (Eu) | 31 (5/26) | 71.1 | 0 | NR | NR | NR | NR | NR | FEV1, FVC, FEV1/FVC, FEF25–75%, DLCO | Good |
| [16] | Ari, 2002 | Turkey (Eu) | 25 (5/20) | 55.6 | 0 | 25.8 | NR | 7.5 | 9.4 | 25 | FEV1, FVC, FEV1/FVC, FEF25–75%, PEF, DLCO | Good |
| [17] | Guazzi, 2002 | Italy (Eu) | 15 (8/7) | 62.3 | 0 | NR | 7.6 | 6.1 | NR | NR | FEV1, DLCO | Good |
| [18] | Maiolo, 2002 | Italy (Eu) | 12 (0/12) | 50.3 | 0 | 32.6 | 11.43 | NR | NR | NR | FEV1, FVC, FEV1/FVC, PEF | Good |
| [19] | Boulbou, 2003 | Greece (Eu) | 33 | NR | 0 | 27.3 | NR | NR | NR | NR | FEV1, FVC, FEV1/FVC, DLCO | Good |
| [20] | Guvener, 2003 | Turkey (Eu) | 25 (9/16) | 56.3 | 0 | 29.9 | NR | 7.4 | 5.8 | 63.6 | FEV1, FVC, PEF, DLCO | Good |
| [21] | Melo, 2003 | Brazil (Am) | 17 (8/9) | 47.0 | 0 | NR | NR | NR | 7.5 | 47 | FEV1, FVC, FEV1/FVC, FEF25–75 | Good |
| [22] | Lau, 2004 | China (As) | 40 (26/14) | 49.8 | 10 | 25.9 | NR | 7.9 | 7.8 | 50 | FEV1, FVC, FEV1/FVC, DLCO | Poor |
| [23] | Sinha, 2004 | India (As) | 29 (21/8) | 46.7 | 0 | 24.9 | 14.54 | 8.6 | 4.4 | 41.4 | FEV1, FVC, PEF, DLCO | Good |
| [24] | Weisbrod, 2005 | Australia (Oc) | 8 (5/3) | 56.2 | 0 | 29.9 | 9.1 | 7.9 | 5.1 | 0 | FEV1, FVC, FEV1/FVC | Good |
| [25] | Meo, 2006 | Saudi Arabia (As) | 32 (32/0) | 52.6 | 0 | NR | NR | NR | 10 | NR | FEV1, FVC, FEV1/FVC, FEF25–75%, PEF | Good |
| [26] | Ortiz-Aguirre, 2006 | Mexico (Am) | 144 (54/90) | 57.7 | 36.8 | 28.8 | 9.16 | NR | 9.2 | NR | FEV1, FVC, FEV1/FVC, PEF | Poor |
| [27] | Ozsahin, 2006 | Turkey (Eu) | 25 (6/19) | 55 | 0 | 24.3 | NR | NR | 9.3 | 92 | DLCO | Fair |
| [28] | Chance, 2008 | USA (Am) | 69 (38/31) | 46.1 | 0 | 31.1 | NR | 8.3 | 7.8 | 38 | FEV1, FVC, FEV1/FVC | Good |
| [29] | Dennis, 2008 | Colombia (Am) | 262 (107/155) | 50.9 | 15.3 | NR | NR | NR | NR | NR | FEV1, FVC, FEV1/FVC | Good |
| [30] | Kabitz, 2008 | Germany (Eu) | 21 (21/0) | 63.6 | NR | 28.5 | NR | 7.3 | 12.9 | 52.4 | FEV1, FVC, FEV1/FVC | Good |
| [31] | Yeh, 2008 | USA (Am) | 1100 (528/572) | 55 | 19 | 30.9 | NR | NR | NR | NR | FEV1, FVC, FEV1/FVC | Good |
| [32] | Ali, 2009 | Bangladesh (As) | 60 (60/0) | 51.8 | 0 | 21.3 | NR | 6.8 | 10.6 | NR | FEV1, FVC, FEV1/FVC | Good |
| [33] | Saler, 2009 | Turkey (Eu) | 68 (19/49) | 52.4 | 0 | 27.0 | NR | 7.4 | 7.6 | 44 | DLCO | Good |
| [34] | Verma, 2009 | India (As) | 50 (30/20) | 50.2 | 0 | NR | NR | NR | NR | NR | FEV1, FVC, FEV1/FVC, FEF25–75%, PEF | Good |
| [35] | Agarwal, 2010 | India (As) | 30 (17/13) | 44.6 | 0 | 22.0 | NR | 8.7 | 5.4 | 50 | FEV1, FVC, FEF25–75%, PEF, DLCO | Good |
| [36] | Ali, 2010, | Bangladesh (As) | 60 (60/0) | 51.8 | 0 | 21.3 | NR | 6.8 | 10.6 | NR | FEF25–75%, PEF | Good |
| [37] | Lecube, 2010 | Spain (Eu) | 25 (0/25) | 44.0 | 0 | 49.2 | 8.6 | 7.5 | NR | 16 | FEV1, FVC, FEV1/FVC, FEF25–75% | Good |
| [38] | Ozoh, 2010 | Nigeria (Af) | 101 (47/54) | 46.1 | 0 | 28.3 | NR | 7.8 | 1 m–18 y | NR | FEV1, FVC, FEV1/FVC, PEF | Good |
| [39] | Buyukhatipoglu, 2011 | Turkey (Eu) | 80 (40/40) | 47.8 | 0 | 26.7 | 10.77 | 9.3 | 5 | 50 | DLCO | Good |
| [40] | Ceylan, 2011 | Turkey (Eu) | 37 (16/21) | 39.8 | 0 | NR | NR | 8.2 | 7 | NR | FEV1, FVC, FEV1/FVC, FEF25–75%, PEF, DLCO | Good |
| [41] | Dharwadkar, 2011 | India (As) | 40 (25/15) | 52.3 | 0 | 22.7 | 8.2 | NR | 6.4 | NR | FEV1, FVC, PEF | Poor |
| [42] | Kim, 2011 | South Korea (As) | 2745 (2168/577) | 55 | 29 | 25.1 | NR | NR | NR | NR | FEV1, FVC, FEV1/FVC | Good |
| [43] | Klein, 2011 | USA (Am) | 76 (33/43) | 63.1 | 29 | 34.2 | NR | NR | 6.7 | NR | FEV1, FVC | Good |
| [44] | Al-Habbo, 2012 | Iraq (As) | 45 (26/19) | 46.7 | NR | NR | NR | NR | NR | NR | FEV1, FVC, FEV1/FVC, FEF25–75%, PEF | Good |
| [45] | Klein, 2012 | USA (Am) | 303 (178/125) | 61.7 | 29.4 | 31.4 | NR | NR | NR | NR | DLCO | Good |
| [46] | Klein, 2012 | USA (Am) | 560 (314/260) | 62.0 | 27 | 31.7 | NR | NR | NR | NR | FEV1, FVC, DLCO | Good |
| [47] | Nandhini, 2012 | India (As) | 45 (30/15) | 47.1 | NR | NR | 7.1 | NR | 6.3 | NR | FEV1, FVC, FEV1/FVC, FEF25–75%, PEF | Good |
| [48] | Abd-El-Azeem, 2013 | Egypt (Af) | 30 | NR | 0 | NR | NR | NR | NR | NR | FEV1, FVC, FEV1/FVC, FEF25–75%, PEF, DLCO | Good |
| [49] | Akber, 2013 | Iraq (As) | 63 (28/35) | 51.0 | 0 | 30.0 | NR | NR | NR | NR | FEV1, FVC, FEV1/FVC | Good |
| [50] | Alkinany, 2013 | Iraq (As) | 60 (60/0) | 40–60 | 0 | NR | NR | NR | NR | NR | FEV1, FVC | Poor |
| [51] | Anandhalakshmi, 2013 | India (As) | 30 | 44.8 | 0 | 26.1 | NR | 6.8 | 7.0 | NR | FEV1, FVC, FEV1/FVC, FEF25–75%, PEF, DLCO | Good |
| [52] | Aparna, 2013 | India (As) | 40 (22/18) | 49 | 0 | 25.2 | NR | NR | NR | NR | FEV1, FVC, FEV1/FVC, PEF | Fair |
| [53] | Rajani, 2013 | India (As) | 40 (19/21) | 46 | 0 | NR | 10.88 | 7.0 | NR | NR | FEV1, FVC, FEV1/FVC, FEF25–75%, PEF | Good |
| [54] | Shafiee, 2013 | Iran (As) | 80 (31/49) | 53.6 | 0 | 28.8 | NR | 8.4 | 9.8 | 50 | FEV1, FVC, FEV1/FVC, PEF | Good |
| [55] | Shah, 2013 | India (As) | 60 (60/0) | 53.9 | 0 | NR | NR | 7.1 | 6.6 | NR | FEV1, FVC, FEV1/FVC, FEF25–75%, PEF | Good |
| [56] | Huang, 2014 | China (As) | 292 (181/111) | 66.8 | 0 | 23.9 | 8.55 | NR | 5.2 | NR | FEV1, FVC, FEV1/FVC | Good |
| [57] | Jamatia, 2014 | India (As) | 30 (19/11) | 57.7 | 0 | 23.5 | 10.71 | 7.93 | >2 | 0 | FEV1, FVC, FEV1/FVC, FEF25–75%, PEF | Good |
| [58] | Uz-Zaman, 2014 | India (As) | 60 | 44.6 | 0 | 24.4 | 9.93 | 7.1 | NR | NR | FEV1, FVC, FEV1/FVC, FEF25–75%, PEF, DLCO | Good |
| [59] | Zineldin, 2015 | Egypt (Af) | 45 (45/0) | 51.1 | 0 | 24.5 | NR | 7.5 | 7.6 | NR | FEV1, FVC, FEV1/FVC, PEF | Good |
| [60] | Buchmann, 2016 | Germany (Eu) | 91 (49/42) | 67.9 | 9.6 | 29.2 | NR | NR | NR | NR | FEV1, FVC, FEV1/FVC | Good |
| [61] | Kaur, 2016 | India (As) | 50 | NR | 0 | NR | NR | NR | NR | NR | FEV1, FVC, FEV1/FVC, PEF | Good |
| [62] | Kumar, 2016 | India (As) | 40 | 50.7 | 0 | 25.4 | 10.6 | 8.5 | 11.1 | 50 | FEV1, FVC, FEV1/FVC, DLCO | Poor |
| [63] | Caron, 2017 | Canada (Am) | 10 (10/0) | 55 | NR | 30.0 | 6.5 | 6.1 | 1.25 | 0 | FEV1, FVC, DLCO | Good |
| [64] | Khafaie, 2017 | Iran (As) | 347 (268/79) | 54.6 | 21 | 26.7 | 7.98 | 8.8 | NR | NR | FEV1, FVC, FEV1/FVC | Poor |
| [65] | k, 2017 | South Korea (As) | 1431 (814/617) | 59.1 | 20 | 25.4 | 7.54 | 7.3 | 4.7 | NR | FEV1, FVC, FEV1/FVC | Good |
| [66] | López-Cano, 2017 | Spain (Eu) | 49 (12/37) | 51.3 | 0 | 42.0 | 9.2 | 8.0 | NR | NR | FEV1, FVC, FEF25–75% | Good |
| [67] | Nidhianand, 2017 | India (As) | 100 (57/43) | 46.6 | 0 | NR | NR | NR | NR | NR | FEV1, FVC, FEV1/FVC, PEF | Good |
| [68] | Shergill, 2017 | India (As) | 50 (50/0) | 52.6 | NR | 23.7 | NR | NR | NR | NR | FEV1, FVC, FEV1/FVC, PEF | Good |
| [69] | Tai, 2017 | China (As) | 63 (34/29) | 53.0 | 0 | 27.7 | 7.9 | 8.0 | 7.8 | NR | FEV1, FVC, FEV1/FVC, DLCO | Good |
| [70] | Wilms, 2017 | Switzerland (Eu) | 65 (19/46) | 46.9 | 27.7 | 44.0 | 8.9 | 7.9 | NR | NR | FEV1, FEV1/FVC | Fair |
| [71] | Okur, 2018 | Turkey (Eu) | 58 (15/43) | 53.3 | NR | 31.7 | 10.27 | 8.2 | 9.9 | NR | FEV1, FVC, FEV1/FVC, FEF25–75%, PEF | Good |
| [72] | Rohling, 2018 | Germany (Eu) | 34 (21/13) | 53.0 | 26.5 | 30.8 | NR | 6.4 | 0.35 | NR | FEV1, FVC | Good |
| [73] | Tayarami, 2018 | Iran (As) | 50 | 58.3 | 0 | NR | NR | NR | NR | NR | FEV1, FVC, FEV1/FVC, FEF25–75%, PEF | Good |
| [74] | Van Eetvelde, 2018 | Belgium (Eu) | 110 (39/71) | 79 | NR | 295 | NR | 6.7 | 10.3 | 74.5 | PEF | Good |
DM: diabetes mellitus; BMI: body mass index; Hb: haemoglobin; T2D: type-2 diabetes; FEV1: forced expiratory volume in 1 s; As: Asia; FVC: forced vital capacity; DLCO: diffusion capacity of the lungs for carbon monoxide; NR: not reported; Am: America; Af: Africa; FEF25–75%: forced expiratory flow between 25–75% of FVC; Eu: Europe; m: months; PEF: peak expiratory flow; Oc: Oceania; y: years.