Study selection
A PRISMA diagram of the search results, including reasons for exclusion, is shown in figure 1. A total of 836 relevant records were identified; however, 243 trials were removed because of duplication. Titles and abstracts were screened for 593 studies, of which 556 were deemed to be unsuitable. The full texts of the remaining 37 articles were screened, and 25 trials were excluded. Finally, nine RCTs were included[29-37].