Table 3. Risk of bias in the included studies.

	Domains of randomized control studies
Study	Random sequence generation	Allocation concealment	Blinding of participants	Blinding of personnel	Blinding of outcome assessment	Incomplete outcome data	Selective reporting
Feiz-erfan et al.	unclear	unclear	low	low	low	low	high
Sys et al.	unclear	low	unclear	unclear	low	high	low
Kubota et al.	low	unclear	low	low	low	low	low
	Domains of Cohort studies
	Representativeness of the exposed cohort	Selection of the nonexposed cohort	Ascertainment of exposure	Demonstration outcome already	Comparability of cohorts	Assessment of outcome	Follow-up time	Adequacy of follow-up of cohorts
Gastro et al.	low	low	low	high	low	high	low	low
Jenis et al.	low	low	low	high	low	low	low	low
Tsai et al.	low	low	low	high	low	high	low	low
Hartmann et al.	low	high	low	low	high	high	low	high
Acebal et al.	low	low	low	high	low	low	low	low
Imagama et al	low	low	low	high	low	low	low	low
Rezende et al.	high	high	low	high	low	high	low	low