Sleep Scientists Say Permanent Standard Time Better Fits the Body Clock

This is not a new experiment. The paper, by Raymond Lam, Ralph Mistlberger, Patrick Baylis and Anita Choi, is a policy analysis that pulls together existing research. It has no participants of its own. Much of the evidence it cites is observational, meaning it finds links between light, sleep and health but cannot prove cause. The authors say the evidence for health effects is accumulated, and they call the effects on economic and education outcomes unclear.

The biology is straightforward. According to the paper, the master clock in the brain runs a little slow, about 24.2 hours per cycle. Daylight resets it each day. Morning light moves the clock earlier. Evening light moves it later. Morning light therefore helps body time match the time set by work and school, and evening light works against that.

Modern life already pushes the clock later, the authors write. Many people spend the day indoors and miss bright morning light. Electric lights and screens extend light into the evening. The result is what researchers call social jet lag: waking for work or school before the body is ready. Observational studies link it to short sleep, poorer mental health, metabolic risk and cognitive problems.

Permanent daylight saving time (pDST) would make this worse in winter, the authors argue. It shifts daylight an hour later, so winter mornings stay dark longer and evenings stay light longer. That works against the body clock at both ends of the day.

Mood is a particular concern. The paper estimates 1% to 3% of people in Canada live with seasonal affective disorder, and as many as 15% have milder winter changes in mood, sleep, appetite and energy. Teenagers aged 12 to 17 are most affected. The leading explanation is a delayed body clock. Early morning bright light is the standard treatment because it shifts the clock earlier. The authors say pDST pushes in the opposite direction.

Geography points the same way, though these are correlations. Seasonal affective disorder prevalence rises by 0.2% for each degree of latitude. In US county data, people living on the western edge of a time zone, where the clock-time sunrise is later, had up to 2 more suicide deaths per 100,000 people each year than those on the eastern edge. A 2025 modelling study found the health benefit of pDST was a third lower than that of permanent standard time (pST).

The paper also describes costs of later solar time. One study found an hour of later sunset reduced weekly sleep by nearly an hour and long-run earnings by about 5%. A Florida study linked an extra hour of morning sunlight to modestly higher adolescent math and reading scores. The authors stress the overall economic and education picture is unclear.

The analysis does not claim standard time is free of trade-offs. Earlier dusk limits evening activities. Earlier summer sunrise may wake some people too early. Light also varies by place, so the effect of either choice differs across Canada, and it matters less near the poles and equator.

The Irish Times, which reported on the paper, quoted Mistlberger: "Our biological clocks need morning light to stay synchronised with the 24-hour day. Permanent daylight saving time moves that light an hour later just when winter mornings are already darkest." The newspaper also cited a 2020 PLoS Computational Biology report of more fatal traffic accidents (up to 30%) and about 4% more heart attacks around the spring change. Those figures come from the coverage, not from the CMAJ text reviewed here.

For individuals, the clock policy is out of their hands, and the CMAJ paper offers no personal advice or plan for adjusting to a clock change; its recommendations are aimed at policy. The Irish Times noted that clocks in Ireland move back on October 25.

Yukon adopted pDST in 2020. British Columbia followed in March 2026, then Alberta and the Northwest Territories. In July, the US House passed a bill for nationwide pDST. What to watch next is whether the US Senate takes up that bill, since the authors say Canada would likely be pressured to follow.

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