Canadian review backs permanent standard time over year-round daylight saving
Canadian researchers recommend permanent standard time over year-round daylight saving if clock changes end, citing morning light. Their review in the Canadian Medical Association Journal rests mostly on observational evidence, so the long-term health effects of any permanent policy remain uncertain.
The Scientist · Science desk
For a Toronto resident waking at 7 am in early January, the dark morning lasts 111 minutes under permanent daylight saving time, against 51 minutes under permanent standard time.
| Figure | Value | Note | Claim |
|---|---|---|---|
| Dark morning, permanent daylight saving time | 111 minutes | 23 | |
| Permanent standard time | 51 minutes | 23 | |
| Wake-up, early January | 7 am | 6 |
What happened
- Psychiatrist Raymond Lam of the University of British Columbia and colleagues weighed published work on rhythms, sleep, mood, education and economics, and compared sunrise times across Canadian cities.
- British Columbia adopted permanent daylight saving time in March, and Alberta and the Northwest Territories have adopted it too and will skip the November clock change.
- In the US, the House passed a bill making daylight saving time permanent on July 14, and a Senate committee received it the next day.
Why it matters
- decision Canadian jurisdictions that adopted year-round daylight saving time have the authors' fallback list: track whether sleep problems, winter depression, absenteeism and road injuries rise.
- constraint The finding does not transfer evenly, because latitude and position within a time zone decide how much the choice matters in a given place.
- exposure Teenagers and young adults may be most exposed to dark mornings, since their body clocks naturally shift later at that age.
- precedent The US dropped year-round daylight saving time within a year of starting it in 1974, citing dark winter mornings for schoolchildren, and Russia reversed its 2011 adoption in 2014.
Morning light is the daily correction the argument turns on. The brain's main circadian clock coordinates sleep and alertness, and it needs daily adjustment to stay in step with the day; morning light moves it earlier and evening light pushes it later [8]. "Imagine a wristwatch that runs 10 minutes slow each day, and every morning you make the 10 minute correction by setting it forward," said Ralph Mistlberger of Simon Fraser University, a co-author, speaking to ScienceAlert [9].
Toronto shows the size of the difference. The latest winter sunrise there, in early January, comes at 7:51 am if standard time is kept all year and at 8:51 am if daylight saving time is kept all year [5]. A resident who wakes at 7 am is up before sunrise under either setting [6]. That is 51 minutes of dark morning under standard time and 111 minutes under daylight saving [23]. Neither option changes the length of the day [7].
When morning light shrinks, sleep rhythms can slip later while school and work still start at the same hour, and getting up on time may mean cutting sleep short [10]. The gap between body clock and schedule is called social jetlag. It has been linked to poorer physical and mental health, as has insufficient sleep [11]. The review applies the same logic to seasonal affective disorder, where one leading explanation is that the body clock slips later when morning light is delayed [12].
Standard time has costs, and the authors list them. Permanent daylight saving time would keep evenings lighter and allow more outdoor activity and socializing. Standard time brings an earlier winter dusk, and an early summer sunrise may wake some people too early [18].
The thing this review doesn't tell you is how big the effect is. ScienceAlert's account reports no effect sizes, and the design, a review of published studies plus sunrise comparisons across cities, can weigh the literature but cannot test either clock directly [4]. The west-of-zone comparison shows the problem. People living farther west within a time zone get later sunrises by the clock, and studies have tied living there to shorter sleep and to some worse health and economic outcomes, but associations like these cannot establish cause [14].
"Later school and work times would help," Mistlberger said [15]. He added that brighter indoor lighting in the morning could also help [16].
We think the case is strongest where winter sunrise falls well after the working day starts, as in Toronto.
What to watch
- Whether the Senate committee acts on the House-passed bill that reached it the day after the July 14 vote.
- How winter mornings are received once Alberta and the Northwest Territories skip the November change; dark school commutes ended the US trial in 1974.
- Whether provinces on year-round daylight saving time publish figures on the outcomes the authors say to track: sleep problems, winter depression, absenteeism and road injuries.
Clarity's read
What the record supports and how the coverage leans. The claims behind it follow.
Reality
- Evidence55
- Adoption
- Insufficient
- Hype gap−10
- Incentives
- Insufficient
- Confidence50
Claim ledger
Ranked by verification strength, evidence, and original report placement.
- [1]
A new Canadian analysis concludes that permanent standard time is the better choice for health if seasonal clock changes are abolished, because it preserves earlier access to morning light.
- [2]
British Columbia adopted permanent daylight saving time in March. Alberta and the Northwest Territories have also adopted year-round daylight saving time and will skip the November clock change.
- [3]
In the US, the House passed a bill to make daylight saving time permanent on July 14, and it was referred to a Senate committee the following day.
- [4]
Psychiatrist Raymond Lam of the University of British Columbia and colleagues assessed the health consequences of standard time and daylight saving time; Ralph Mistlberger of Simon Fraser University co-authored the peer-reviewed analysis, which reviewed published research on biological rhythms, sleep, mood, education and economic effects, examined countries' experiences with permanent time policies, and compared sunrise and sunset times across Canadian cities.
- [5]
In Toronto, the latest winter sunrise, in early January, would come at 7:51 am under permanent standard time and 8:51 am under permanent daylight saving time.
- [6]
A Toronto resident waking at 7 am in early January would get up before sunrise under either setting.
- [7]
Neither option changes the length of the day.
- [8]
The brain's main circadian clock coordinates sleep, alertness and other daily functions. It needs daily adjustment to stay in step with the day. Morning light helps move it earlier, while evening light pushes it later.
- [9]
"Imagine a wristwatch that runs 10 minutes slow each day, and every morning you make the 10 minute correction by setting it forward,"
- [10]
With less morning light, sleep rhythms can slip later while school and work still begin at the same hour. Getting up on time may mean cutting sleep short.
- [11]
Social jetlag, the gap between the body clock and school or work schedules, has been linked to poorer physical and mental health, as has insufficient sleep.
- [12]
The researchers considered seasonal affective disorder, a form of depression often experienced in winter. One leading explanation involves the body clock slipping later when morning light is delayed.
- [13]
Teenagers and young adults may be especially vulnerable because their body clocks naturally shift later at that age.
- [14]
People living farther west within a time zone get later sunrises by the clock. Studies have linked this position with shorter sleep and some poorer health and economic outcomes, though these associations do not prove causation.
- [15]
"Later school and work times would help,"
- [16]
Mistlberger added that brighter indoor lighting in the morning could also help.
- [17]
The US introduced year-round daylight saving time in 1974 and abandoned it within the year, following concerns about dark winter mornings and children traveling to school before sunrise. Russia adopted it in 2011 and reversed it in 2014.
- [18]
Permanent daylight saving time would keep evenings lighter, allowing more time for outdoor activity and socializing. Standard time brings earlier winter dusk, while early summer sunrise may wake some people too early.
- [19]
Latitude and location within time zones also determine how much the choice matters in a given place.
- [20]
Much of the evidence comes from observational research and geographic comparisons, leaving uncertainty about permanent policies' long-term health consequences.
- [21]
The researchers recommend permanent standard time. If governments choose year-round daylight saving time, they advise considering later school and work starts, improving morning light exposure, and tracking whether sleep problems, winter depression, absenteeism, and road injuries rise.
- [22]
The research has been published in Canadian Medical Association Journal.
- [23]
For a Toronto resident waking at 7 am in early January, the dark morning lasts 51 minutes under permanent standard time and 111 minutes under permanent daylight saving time.
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