Data extraction and synthesis
Two investigators (MBE and CJG) independently selected eligible systematic review. Disagreement was resolved by discussion with another investigator (VM). Data on all-cause mortality was sought, synthesized, analysed, critically examined and interpreted from systematic reviews and primary studies. We extracted odds ratio (ORs), relative risk (RRs), or hazard ratios (HRs) from the included studies with 95% CI. We did not reanalyze the authors’ original data or conduct new meta-analyses by combining studies.