TABLE 1.
Characteristics of the included studies.
| Author | Year | Country/Region | Study Design | DM type | Sample size | Sex (Male/Female) | Age (year, mean ± SD or median (range)) | Method | NOS |
| Abd El Dayem (16) | 2015 | Egypt | cross-sectional | 1 | 92 | DM: 31/31 | 16.32 ± 1.52 | ELISA | 6 |
| C: 15/15 | 16.3 ± 2.63 | ||||||||
| Nielsen (24) | 2010 | Denmark | cross-sectional | 1 | 204 | 118/86 | 38 ± 12.6 | ELISA | 8 |
| Panduru (25) | 2013 | Australia | cross-sectional | 1 | 2454 | DM: 1126/1120 | NA | ELISA | 8 |
| C: 106/102 | 35.9 ± 11.3 | ||||||||
| Suh (26) | 2016 | South Korea | cross-sectional | 1 | 61 | DM: 12/17 | NA | ELISA | 7 |
| C: 13/19 | 11.91 ± 3.61 | ||||||||
| Chou (27) | 2013 | Taiwan/China | longitudinal | 2 | 140 | 72/68 | 56.6 ± 9.8 | ELISA | 6 |
| Thi (6) | 2020 | Vietnam | cross-sectional | 2 | 136 | 60/76 | NA | ELISA | 7 |
| Eynatten (28) | 2010 | Germany | cross-sectional | 2 | 170 | 125/45 | DM:60.7 ± 7.4 | ELISA | 8 |
| C:51.9 ± 9.5 | |||||||||
| Fufaa (29) | 2015 | the Gila River Indian Community | longitudinal | 2 | 260 | 82/178 | 42.5(18.7-65.1) | ELISA | 8 |
| Gohda (30) | 2018 | Japan | cross-sectional | 2 | 314 | 166/148 | 64 ± 13 | ELISA | 7 |
| Ito (31) | 2017 | Japan | cross-sectional | 2 | 788 | 457/331 | 66 ± 12 | ELISA | 6 |
| Kamijo (32) | 2011 | Japan | cross-sectional | 2 | 552 | 88/52 | NA | ELISA | 7 |
| Suzuki (33) | 2005 | Japan | cross-sectional | 2 | 356 | 229/127 | 63 ± 11 | ELISA | 7 |
| Viswanathan (34) | 2015 | India | cross-sectional | 2 | 78 | 45/33 | NA | ELISA | 7 |
DM, diabetes mellitus; C, control; NOS, Newcastle-Ottawa Scale; NA, Not Available; ELISA, enzyme linked immunosorbent assay.