Footnotes

• Contributors J-HZ conceived the study, and J-HZ and B-DX designed the search strategy and statistical analysis. J-HZ, Y-XT and M-JL collected the data. J-HZ drafted and revised the manuscript. J-HZ is guarantor of the study. All authors had full access to all the data in the study and can take responsibility for data integrity and accuracy of the data analysis. All authors approved the final version of the article.

• Funding This work was supported by the Graduate Course Construction Project of Guangxi Medical University (YJSA2017014), the Foundation Ability Enhancement Project for Young Teachers in Guangxi Universities (2018KY0122) and ‘Guangxi BaGui Scholars’ special fund.

• Competing interests None declared.

• Patient consent for publication Not required.

• Ethics approval This was a comprehensive review, and all the included studies have obtained this approval from their own institutions.

• Provenance and peer review Not commissioned; internally peer reviewed.