At 2 a.m. on Sunday, 1 November, most people in the United States will set their clocks back an hour. The date is not a convention but a statute: the Energy Policy Act of 2005 put the end of daylight saving time on the first Sunday in November, the rule the US Naval Observatory still publishes.

The reward is one extra hour of weekend, followed by several weeks of dark afternoons. It is tempting to file the whole ritual under annoyance. Two papers published this year make a better case for paying attention, because the autumn change turns out to be the comparatively benign half of the twice-yearly switch — and because the question that follows it has no settled answer: if the switching ever stops, which time should we keep?

What the week after the change looks like

The largest recent test of the transitions comes from England. In a population-based cohort in The BMJ on 17 December 2025, researchers at Bristol and UCL used the Clinical Practice Research Datalink, linked to hospital admissions and emergency department records, and followed 683,809 people who had a health event in the eight weeks surrounding a clock change between 2008 and 2019. Negative binomial models compared event rates in the week after each change against a control period.

For the autumn change the direction was consistent across five conditions. Anxiety events fell from 17.3 to 16.7 per day (incidence rate ratio 0.97, 95% confidence interval 0.95 to 0.98), acute cardiovascular disease from 50.0 to 48.9 (0.98, 0.96 to 0.999), depression from 44.6 to 42.7 (0.96, 0.95 to 0.97), psychiatric conditions from 3.5 to 3.3 (0.94, 0.90 to 0.98) and sleep disorders from 5.4 to 4.9 (0.92, 0.87 to 0.97). There was little evidence of change for eating disorders, road traffic injuries or self-harm. For the spring change, there was little evidence of change in any direction.

Two caveats belong with those numbers. The data are coded health records, so they date a clinician’s entry rather than the first symptom, and the design is observational: it describes an association inside one country’s health system, not a mechanism. Still, the asymmetry is the finding. An hour gained in autumn does not look, in the record, like an hour lost in spring.

The question that outlives the clock change

Canada is where the policy argument has moved fastest. Yukon has been on permanent daylight saving time since 2020; British Columbia adopted it in March 2026, and Alberta and the Northwest Territories followed a month later. In July 2026 the US House of Representatives passed a bill to make daylight saving time permanent nationwide; it is currently before the Senate.

An analysis in CMAJ on 4 October 2026 takes that as its starting point. Raymond Lam (psychiatry, University of British Columbia), Ralph Mistlberger (psychology, Simon Fraser University), Patrick Baylis (Vancouver School of Economics) and Alexandra Choi (Vancouver Coastal Health) set aside the question of whether to stop changing clocks and ask which permanent standard a jurisdiction should pick instead: standard time or daylight saving time.

The difference is not abstract. Under permanent daylight saving time, Vancouver’s latest winter sunrise would fall at 9:08 rather than 8:08; Toronto’s at 8:51 rather than 7:51; Montréal’s at 8:35 rather than 7:35. Summer evenings gain the same hour at the other end of the day.

The biology behind the authors’ preference is not seriously contested. The master clock in the hypothalamus runs slightly slow, at roughly 24.2 hours, and needs morning light to stay aligned with the 24-hour day; evening light pushes it later. Modern indoor life already weakens the first cue and strengthens the second, producing the mismatch known as social jet lag. Permanent daylight saving time stretches winter morning darkness and evening light in the same direction as that mismatch, at both ends of the day.

What they put on the scales

The authors attach numbers to the stakes. An estimated 1% to 3% of people in Canada live with winter depression, and as many as 15% experience milder seasonal shifts in mood, sleep, appetite and energy, with prevalence rising about 0.2% per degree of latitude. In US county-level analyses, people living on the western, late-sunrise edge of a time zone averaged as many as two additional suicide deaths per 100,000 people each year compared with those on the eastern edge, with wider gaps in northern regions. A 2025 modelling study cited in the analysis found both permanent options better than the current switching, but put permanent daylight saving time’s health advantage a third below permanent standard time’s.

The economic and educational literature points the same way, if less firmly. One study found that an hour of later sunset reduces weekly sleep by nearly an hour and long-run earnings by about 5%; workers on the late-sunset side of US time-zone borders were estimated to earn about 3.5% less. At schools straddling a time-zone boundary in Florida, students with an extra hour of sunlight before school scored 0.08 standard deviations higher in maths and 0.06 in reading. All of it is quasi-experimental, and the authors say so.

The counter-reading

A systematic review in the European Journal of Epidemiology, published online on 21 February 2026, reaches a more guarded conclusion. The team searched five databases to June 2025 and synthesised 157 studies from 36 countries, appraising them with the Joanna Briggs Institute checklist for quasi-experimental work.

Its central finding is a warning about the message. The idea that transitions, and daylight saving time through the summer, are uniformly detrimental “is not supported”. Spring onset transitions were associated with more acute myocardial infarctions and fatal traffic accidents, but also with fewer crimes involving physical harm. Autumn offset transitions were associated with lower all-cause mortality and fewer workplace accidents, but with more crimes involving physical harm. Living on daylight saving time, rather than standard time, was associated with lower all-cause mortality and fewer traffic accidents in summer, while standard time was potentially associated with shorter sleep in winter. The reviewers found no clear and consistent psychiatric effects. Their recommendation is neither to keep nor to abolish the switch, but to mitigate risks while better evidence accumulates.

Read together, the two papers do not collide over Sunday’s change; they agree it is not the damaging one. They part ways on the destination, where one argues from circadian biology and the other from an epidemiological record it describes as limited and heterogeneous.

What has already been tried

The American Academy of Sleep Medicine supports permanent standard time. Its position rests on alignment with circadian rhythms, and it points to research linking the biannual switch to accidents, cardiovascular problems and mood disturbance.

History offers its own cautions about the other option. The United States adopted permanent daylight saving time in 1974 as an energy measure and abandoned it within the year, after objections to dark winter mornings and concern about children travelling to school before sunrise. Russia moved to permanent summer time in 2011 and reversed the policy in 2014; Chile did the same in 2015, keeping the change only in its far-southern Magallanes region.

What the coming weeks actually require

For most people the practical questions are much smaller than the policy ones. Standard sleep guidance does not move with the clock: the CDC lists seven or more hours a night for adults aged 18 to 60, seven to nine for 61 to 64, and seven to eight for those 65 and older. The research on consistency of sleep timing is a different matter from the hour itself.

Seasonal mood changes are their own subject. NIMH describes winter-pattern seasonal affective disorder as symptoms lasting about four to five months, and describes light therapy — a 10,000-lux box for roughly 30 to 45 minutes, usually in the morning, from autumn to spring — as a mainstay, with the caution that people with certain eye conditions or light-sensitising medications may need supervision. Evidence on vitamin D as a treatment remains mixed, as our earlier look at autumn light and vitamin D noted.

The CMAJ authors’ mitigation list is addressed to governments, not individuals: street lighting and sidewalks, reflective gear for schoolchildren, later or flexible start times, brighter morning light in schools and workplaces, clinician education, and surveillance broken down by age, sex, geography, income, rurality and shift-work exposure. Little of it is settled policy anywhere. What the record does support is the shape of the next argument: whether to stop changing the clocks has become the easy question, and which time to keep is the one still waiting on evidence.

This article reports on published research and public guidance and is not medical advice, in line with our medical disclaimer. Anyone whose sleep or mood shifts substantially with the seasons should raise it with a healthcare professional.