Table 3. Risk of bias assessment of the included studies.

Author	Was the selection of exposed and nonexposed cohorts drawn from the same population?	Can we be confident in the assessment of exposure?	Can we be confident that the outcome of interest was not present at the start of the study?	Did the study match exposure and nonexposure for all variables that are associated with the outcome of interest or did the statistical analysis adjust for these prognostic variables?	Can we be confident in the assessment of the presence or absence of prognostic factors?	Can we be confident in the assessment of the outcome?	Was the follow-up of cohorts adequate?	Were co-interventions similar between groups?
Devreese et al. (29)	Definitely low risk	Probably low risk	Probably low risk	Probably high risk	Definitely low risk	Probably high risk	Definitely high risk	Probably high risk
Thompson et al. (38)b	Probably high risk	Probably high risk	Probably low risk	Probably low risk	Definitely low risk	Probably high risk	Definitely high risk	Probably high risk
Madill et al. (31)	Probably low risk	Probably high risk	Probably low risk	Probably low risk	Definitely low risk	Definitely low risk	Definitely high risk	Probably high risk
Arab et al. (24)	Probably low risk	Probably low risk	Probably low risk	Probably low risk	Probably low risk	Probably high risk	Definitely high risk	Probably high risk
Tajiri et al. (36)	Probably high risk	Probably high risk	Probably low risk	Probably high risk	Definitely low risk	Probably high risk	Definitely high risk	Probably high risk
Ptaszkowski et al. (34)	Definitely low risk	Probably low risk	Probably low risk	Probably low risk	Definitely low risk	Probably high risk	Definitely high risk	Probably high risk

^bThompson et al. study (38).