Table 4. Quality assessment conducted according to the Newcastle-Ottawa Scale for all the included studies.

First author and Ref. no.	Quality indicators
	Selection	Comparability	Exposure
Wu et al.11	***	*	**
Chen et al.12	***	*	***
Chen et al.13	***	*	***
Garcia et al.14	**	*	**
Heidi et al.15	***	*	**
Araujo et al.16	***	*	**
Singla et al.17	***	*	***
Thye et al.18	****	*	***
de Wit et al.19	***	*	**
Capparelli et al.20	***	*	**
Cossar et al.21	**	*	**
Alagarasu et al.22	***	*	*
Soborg et al.23	***	*	*
Liu et al.24	***	*	***
Garcia et al.25	****	*	**
Selvaraj et al.26	***	*	*
Fitness et al.27	****	*	**
Soborg et al.28	***	*	**
Ozbaş et al.29	*	*	**
Selvaraj et al.30	***	*	**
Hoal et al.31	****	*	**
Bellamy et al.32	**	*	**