1.2 Inclusion and exclusion criteria
We only included the observational studies which satisfied the following criteria: (1) assessed the effect of BW on the risk of adult-onset cancers; (2) the effect values including hazard ratios (HRs) or odds ratios (ORs) and 95% confidence intervals (95% CIs) were reported or provided sufficient data to calculate them; (3) studies have a clear dose representation of BW, a number of cancer cases corresponding to BW or provide sufficient data to calculate them; (4) prospective cohort studies or case-control studies. We did not include conference abstracts or unpublished or grey literature, anecdotal reports, or case series, or manuscripts published in any language other than English.