Daylight-Saving Time & Health: A Systematic Review of Beneficial & Adverse Effects

Background Whether to maintain biannual time transitions or adopt perennial daylight-saving time (DST) or Standard Time is widely debated but health impacts have not been comprehensively reviewed. Method Five literature databases were screened to September 01, 2024. Effects of transitions and living with DST or Standard Time on all-cause mortality, accidents, cardiovascular-, gastrointestinal-, psychiatric-, neurologic-, cognitive-, and circadian- or sleep-related outcomes were included. The Joanna Briggs Institute’s Checklist for Quasi-Experimental Studies was used to assess quality. Findings N=149 studies of various designs, locations (36 countries), and quality were identified. The evidence suggests DST-Onset transitions increase risk of acute myocardial infarction (17 studies, 5 high quality) and fatal traffic accidents (14 studies, 3 high quality) but decrease crimes involving physical harm (5 studies, 3 high quality). By contrast, DST-Offset transitions are associated with decreased all-cause mortality (3 studies, 1 high quality), fatal traffic accidents, and workplace accidents (8 studies, 1 high quality), but increased crimes involving physical harm. DST-Onset is only observed to affect sleep duration in individuals with early school or work start times, whereas DST-Offset appears to increase duration (17 studies, 2 high quality). Sleep timing shifts of <1-hour following transitions may occur, but are not indicative of circadian disruption. No studies clearly identify effects on psychiatric outcomes (15 studies, 1 high quality) or circadian rhythm disruptions (7 studies, 0 high quality). Living with DST during summer and winter is associated with decreased all-cause mortality and sleep duration, respectively (2 studies, 1 high quality). Interpretation Benefits of DST during summer on mortality, of DST-Offset transitions on sleep and mortality, and of Standard Time during winter on sleep argue in favour of maintaining transitions. Adverse effects of transitions could be mitigated by strategies to protect individuals at risk of myocardial infarction, reduce traffic accidents, and prevent crimes. Funding None. Evidence before this study The abolition of daylight-saving time (DST) transitions in favour of perennial DST or Standard Time has been called for but health impacts have not been comprehensively reviewed. Added value of this study N=149 original research studies that comprise various study designs, populations, and locations (36 countries worldwide) were identified, critically appraised, and synthesised in this study. Transitions between DST and Standard Time, living with DST or Standard Time between transitions or perennially, or living at different longitudes in a given time zone are considered as exposures. An extensive list of outcomes can be broadly categorised into all-cause mortality, accidents, cardiovascular-, gastrointestinal-, psychiatric-, neurologic-, cognitive-, and circadian- or sleep-related health outcomes. The present study is the most comprehensive systematic review of effects of transitions or living with DST vs Standard Time on health, which can contribute to an evidence-based debate. Implications of all the available evidence The apparent benefits of DST during summer months on mortality, DST-Offset on sleep duration and mortality, and Standard Time during winter months on sleep duration argue in favour of keeping transitions. If kept, adverse effects of transitions should be mitigated in individuals susceptible to myocardial infarction or exacerbations of disease. Strategies to reduce both traffic accidents following DST-Onset and crime following DST-Offset could also provide benefit. The exact mechanisms of DST-Onset strain (or benefit of DST during summer months and benefit of DST-Offset) remain open. Additional open questions pertain to the severity of transition effects in different locations, by susceptibility of individuals to health effects, and baseline risks of traffic accidents and crimes. From a health perspective, working toward keeping the good and mitigating the bad associated with transitions and DST may be warranted. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement No funding was received for this study. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. 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Yes All extracted data is provided in the main text and appendix.