Quality assessment
To assess the methodological quality of the included studies we used the Cochrane risk-of-bias tool for randomized trials22. The quality of all studies was assessed on the following domains: random sequence generation, allocation concealment, blinding of participants and personnel, blinding of outcome assessment, incomplete outcome data, selective reporting and other sources of bias. Each item was rated as low, unclear or high risk of bias, based on the information reported (table S4). Studies were classified as high quality (not fulfilling 0-1 criterion), moderate (not fulfilling 2-3 criteria), and low quality (not fulfilling >3 criteria).