Table 2.

Assessment of study quality

References	Quality indications form of Newcastle-Ottawa Scale									Total stars
	1	2	3	4	5A	5B	6	7	8
Fishbane et al. 1996 [8]	☆	☆	☆	☆	☆	☆	☆	-	☆	8
Ono et al. 2003 [9]	☆	☆	☆	☆	☆	☆	☆	-	☆	8
Rajagopalan et al.2006 [10] Vega et al.2008 [17]	☆ ☆	☆ ☆	☆ ☆	☆ ☆	☆ ☆	☆ -	☆ ☆	☆ -	☆ ☆	9 7
Cohen et al.2010 [11]	☆	☆	-	☆	☆	☆	☆	-	☆	7
Adragao et al. 2012 [12]	☆	☆	☆	☆	☆	☆	-	-	☆	7
Otsubo et al. 2012 [13]	☆	☆	☆	☆	☆	☆	☆	☆	-	8
Thani et al. 2013 [14]	☆	☆	☆	☆	☆	☆	-	-	-	6
Tsai et al. 2015 [15]	☆	☆	☆	☆	☆	☆	☆	☆	☆	9
Zhou et al. 2015 [16]	☆	☆	☆	☆	☆	☆	☆	☆	☆	9

For cohort studies: 1, exposed cohort truly or somewhat representative; 2, nonexposed cohort drawn from the same community as the exposed cohort; 3, ascertainment of exposure; 4, outcome of interest not present at start; 5A, study controls for age; 5B, study controls for ≥ 3 additional risk factors; 6, assessment of outcome (independent blind assessment or record linkage); 7, follow-up ≥ 62 m; 8, complete accounting for cohorts or subjects lost to follow-up unlikely to introduce bias.

“☆”was scored 1 and “-” was scored “0”.