Abstract Our objective was to systematically review the epidemiological evidence regarding health effects of daylight-saving time (DST) practices – the abolition of which have been called for without the epidemiology having been comprehensively reviewed. We searched PubMed, Web of Science, Scopus, PsychINFO, and EconLit up to June 2025. The primary inclusion criterion was human studies that consider either acute effects of transitions or DST vs standard time at a given time of year. Included studies were critically appraised using the Joanna Briggs Institute Critical Appraisal Checklist for Quasi-Experimental Studies. We narratively synthesize by broader outcome categories in Supplementary Material and provide a synthesis of syntheses in the main text. From 157 studies of varying designs and quality from 36 countries, we find that the messaging of transitions and DST during summer months being uniformly detrimental is not supported. DST-Onset transitions appear associated with increased acute myocardial infarction and fatal traffic accidents, but also with decreased crimes involving physical harm. DST-Offset transitions appear associated with decreased all-cause mortality and workplace accidents, but also with increased crimes involving physical harm. Living with DST (compared to Standard Time) appears associated with decreased all-cause mortality and traffic accidents in summer. Standard Time appears is potentially associated with decreased sleep duration during winter. No clear and consistent effects on psychiatric outcomes are identified. Limited studies prevent clear conclusions being drawn regarding other sleep parameters or circadian rhythms. This review indicates that transitions and living with DST (as opposed to Standard Time) during summer months are not uniformly detrimental; however, the evidence base remains limited and heterogeneous. Rather than advocating for maintaining or removing transitions, our synthesis supports a balanced approach. We recommend recognising both adverse and beneficial patterns and prioritising strategies to mitigate risks while awaiting more robust evidence. Registration https://doi.org/10.17605/OSF.IO/R4W6M