Risk of bias (quality) assessment: Randomized controlled trials will be assessed with the Jadad scale and the score of the Cochrane Collaboration, taking into account the domains of randomization, blinding, allocation concealment, withdrawals and dropouts. Observational studies will be evaluated with the ROBINS-I tool, which assesses the domains of confounding, selection of participants, classification of interventions, deviation from intended intervention, missing data, measurement and reporting of the outcomes. Both tools will be indepedently implemented by two researchers, while any potential disagreements will be resolved by their consensus. The credibility of outcomes will be evaluated on the grounds of within-study bias, across-studies bias, indirectness, imprecision, heterogeneity and incoherence.