Fig. 1

Flow diagram of the selection process. Initially, 3007 documents were retrieved, of which 2495 remained after duplicates were removed. After screening the titles and abstracts, 451 irrelevant studies, 5 case reports, 10 reviews, 7 animal studies, 7 clinical trials without results, 33 conference abstracts, 5 studies in other languages, 35 studies lacking a control group, and 12 studies with other reasons were excluded. Ultimately, 6 documents were included in this meta-analysis