Table 3.

GRADE approach for the primary outcome

Outcome	Quality assessment
	Required domains					Additional domains			Grade
	Study limitations	Consistency	Directness of evidence	Precision	Reporting bias	Dose-response association	Plausible confounding that would decrease the observed effect	Strength of association (magnitude of effect)
Asthma	Higha	Inconsistentb	Indirect	Precisec	Undetectedd	Undetected	Presente	Weakf	Low
Allergic rhinitis	Higha	Inconsistentb	Indirect	Precisec	Unestimableg	Undetected	Presente	Weakf	Very low

^aAll included studies are observational in design

^bConsiderable heterogeneity (I² > 50%)

^cVery large sample size (over 4000)

^dAccording to Egger’s regression test (p = 0.578)

^eAll included studies had an observational design, and there was a difference in adjusted variables depending on each study

^fOR < 2.0

^gDue to insufficient included studies to evaluate publication bias