Quality assessment
Two authors independently assessed the quality of the methodology for each study using the Newcastle-Ottawa scale adapted for cross-sectional studies 13. The assessment tool comprised of three scales; selection (maximum of five stars), comparability (maximum of two stars), outcome (maximum of three stars) and graded out of 10 points (stars). This assessment critically appraised the internal (systematic error) and external validity of the studies to reduce the risk of biases. The scale is composed of seven items and classifies the study in four possible levels: very good (9-10 points), good (7-8 points), satisfactory (5-6 points) and unsatisfactory (0-4 points). Any disagreement was resolved through consensus (supplementary Table S3).