The twice-yearly ritual of changing our clocks — Spring forward, Fall back — may be headed for the history books, but a new question is taking its place: If we stop changing the clocks, which time should we live by?

An analysis published in CMAJ, the Canadian Medical Association Journal concludes that, from a health perspective, permanent standard time seems to be the better choice.

The researchers examined evidence on sleep, circadian rhythms, mood, safety, productivity and other health-related outcomes to compare permanent standard time with permanent daylight savings time.

“We have focused for years on whether to stop changing the clocks. The more important question now is what happens the morning after we stop.”

The analysis was prompted by a policy debate unfolding in several Canadian jurisdictions that are considering ending the seasonal clock change. The researchers point out that eliminating the clock change does not settle the issue. Governments must decide whether clocks should remain on standard time or daylight savings time year-round. The analysis was led by researchers from the University of British Columbia, Simon Fraser University and Vancouver Coastal Health.

The distinction matters because daylight is one of the strongest signals regulating our body's internal clock. Morning light helps synchronize circadian rhythms, while exposure to light later in the day can delay them.

Permanent daylight savings time would shift sunrise an hour later, meaning that during winter, more people would wake up, travel to school and commute to work in darkness.

Permanent standard time is not without a downside. Winter evenings would become darker earlier, something people dislike.

“The health evidence points to standard time, largely because morning light matters for our body clocks, sleep, and mood,” says lead author, Raymond W. Lam, professor of psychiatry at the University of British Columbia in Vancouver. Lam and his colleagues note that major sleep and chronobiology organizations recommend permanent standard time. Their analysis also draws on geographic research showing that people living farther west within a time zone, where sunrise occurs later according to the clock, experience several adverse health outcomes.

Sleep and mood are concerns. The authors note that an estimated 1 percent to 3 percent of Canadians experience seasonal affective disorder, while as many as 15 percent experience milder seasonal changes in mood, sleep, appetite and energy. Later winter sunrises could make those problems more difficult for some people.

Children and teenagers may be especially vulnerable. Puberty naturally shifts sleep schedules later, yet school often starts early. A later sunrise could further separate young people's biological clocks from their schedules. Shift workers, early-start workers, commuters, pedestrians and cyclists may also face challenges, particularly in communities with limited lighting and transportation infrastructure.

Permanent standard time is not without a downside. Winter evenings would become darker earlier, something people dislike. The authors acknowledge that this could affect recreation and social activity, although they say those disadvantages appear easier to address than the health concerns associated with delayed winter sunrises.

Morning light helps synchronize circadian rhythms, while exposure to light later in the day can delay them.

Permanent daylight savings time does have an appeal — more light after work and school. That extra daylight can encourage exercise, socializing and shopping. But Patrick Baylis, associate professor at the Vancouver School of Economics at UBC, says those benefits must be weighed against evidence connecting later solar time with less sleep, lower productivity and poorer educational outcomes.

History offers another caution. The United States tried permanent daylight savings time in 1974 but returned to standard time within a year, amid opposition to dark winter mornings and concerns about children traveling to school before sunrise. Russia and Chile reversed daylight saving time policies, too.

The researchers conclude that the health evidence favors permanent standard time. They also argue that whichever system governments choose should be monitored for effects on sleep, mood, injuries and other outcomes. “We have focused for years on whether to stop changing the clocks,” Lam says. “The more important question now is what happens the morning after we stop.”