Synthesis of findings.

Raw data are presented as mean±SD (standard deviation), unless otherwise indicated. MD: mean difference; RR: risk ratio; aOR: adjusted odds ratio; CI: confidence interval.*Mean difference (MD), confidence interval (CI) and p-value were calculated by the reviewer(s) using Review Manager software¥ Imprecision (large variability of results)† Imprecision (lack of data)§ Imprecision (limited sample size)Synthesis of findings.