Table 2.

Methodological quality of the included studies using the NOS scale [45]

Cohort studies	Selection	Comparability	Outcome	Conclusion
Oliver et al	****	*	***	8
Ayala et al	****		***	7
López-Valenciano et al	****		***	7
Rommers et al	****		***	7
Rossi et al	**		***	5
Carey et al	**		***	5
Ruddy et al	****		***	8
Thornton et al	**		***	5
McCullagh & Whitfort	****		***	7
Case–control studies	Selection	Comparability	Exposure	Conclusion
Rodas et al	****		***	7
Whiteside et al	****		***	7