Table 2. Quality assessment of the included studies based on the Newcastle–Ottawa Scale.

Publication year	Study design	Selection	Comparability	Exposure/Outcome	Total scores
Abdallah17	Cross-section	★★★★	★★	★★	8
Correia14	Cross-section	★★★	★	★★	6
Croen19	Case-control	★★★★	★★	★★	8
Halepoto25	Cross-section	★★★★	★★	★★	8
Hashimoto13	Cross-section	★★★	★★	★★	7
Kasarpalkar26	Cross-section	★★★★	★★	★★	8
Katoh-Semba23	Cross-section	★★★	★★	★★	7
Miyazaki24	Cross-section	★★★★	★	★★	7
Nelson18	Case-control	★★★★	★	★★	7
Nelson20	Case-control	★★★★	★★	★★	8
Ricci15	Cross-section	★★★	★★	★★	7
Wang16	Cross-section	★★★★	★★	★★	8
Zhang21	Cross-section	★★★★	★★	★★	8
Meng22	Cross-section	★★★	★★	★★	7