Table 2.

Risk of bias summary: review of authors’ judgments about the risk of bias in each study included

References	Representativeness of the cases	Selection of control	Ascertainment of exposure	Interest outcome not present at start cohorts of study	Comparability of cohorts	Control for any additional factors	Assessment of outcome	Enough follow up	Adequacy of follow up
Baumfeld et al. [9]	–	–	–	–	+	+	+	+	–
Kong et al. [10]	–	–	–	–	+	+	+	+	–
Lopes et al. [11]	–	–	–	–	–	+	+	+	–
Saygi et al. [12]	–	–	–	–	+	+	+	+	–
Srinivas et al. [13]	–	–	–	–	+	+	+	–	–
Uzumcugil et al. [14]	–	–	–	–	+	+	+	+	–

+ low risk of bias, − high risk of bias