Trump pushes the US to adopt pDST, but Canadian researchers say darker mornings come with costs for sleep, learning, and productivity
President Trump is pushing hard for the US Senate to make daylight saving time permanent so, among other things, golfers can stay on the course longer, but it may not be such a bright idea. New research out of Canada suggests that, even if Americans would get an extra hour of daylight in the evening, the ill health effects of permanent daylight saving time could outweigh the benefits.
A paper published in the Canadian Medical Association Journal on Monday reviewed evidence on the health effects of permanent daylight saving time (pDST) as several Canadian jurisdictions move to stop changing their clocks. It finds that the opposite approach - adoption of permanent standard time (pST) - would actually be better for people’s health.
Sorry, night owls and after-work social butterflies, but the science simply isn’t with you on this one.
“Permanent DST preserves later evening light that may facilitate commuting, recreation, social participation, and some economic activity, but it also prolongs darkness on winter mornings,” the authors note. Prolonged morning darkness doesn't really jibe with the inner workings of the human body and light’s essential role in regulating the circadian rhythm. Sure, no one wants to drive home from work in the dark, but we really need morning light to get us functioning properly.
Our circadian rhythms, the authors explain, actually run on a slightly longer schedule than a full day - 24.2 hours. For that reason, we rely on natural sunlight to keep us synchronized with the world around us. Morning light is some of the most important, the authors note, because it jump starts that rhythm, wakes us up and gets us moving. Evening light, on the other hand, delays the circadian rhythm, messing with our sense of “social time” and making it tougher to get to sleep and wake up rested in the morning.
The effects of later evening light can show up in sleep, mood, education, and work productivity, the authors noted, and we don’t even need pDST to see some of those associations - we can just look at time zones.
Move from east to west in the US or Canada and you’ll get some considerable differences in when the sun rises and sets in a particular time zone - in some cases, sunrise and sunset can differ by more than an hour of clock time across a single time zone.
In one study cited by the Canadian analysis, residents on the western side of US time zones, where the sun sets later, got around an hour less sleep a week. The study also estimated that an additional hour of sleep per week was associated with around 5 percent higher long-term earnings. Similar results turned up in a German study, the team noted. Another study found that workers on the western end of US time zones ended up working fewer hours, too.
On the educational front, an extra hour of sunlight before school was associated with higher math and reading scores in a Florida study “comparable in magnitude to meaningful class-size reductions.”
“Ending biannual clock adjustments may eliminate transition harms that last a few weeks, but the health effects of permanent time are likely to be chronic,” the authors noted. “The preponderance of health evidence favors pST, which would align with the recommendations of sleep and chronobiology societies worldwide.”
This isn’t the first time researchers have concluded such. British sleep scientists concluded much the same in 2024, which led to their recommendation to permanently kill DST in favor of a permanent shift to Greenwich Mean Time.
That isn’t stopping the US from plowing ahead with plans for pDST, though. The Senate passed a measure to enshrine DST in 2022, but the House never acted on it. This time around, the House has passed its own bill to enact pDST, but the Senate is dithering, leading President Trump to go so far as to post the personal cellphone number of one Republican holdout on social media, Senator Tom Cotton (R-AR), who is opposed to the measure.
“No one likes changing the clock, me included, but Congress has enacted permanent Daylight Savings Time multiple times before and repealed it each time once Americans experienced absurdly late sunrises in the winter,” Cotton explained in a post on X following Trump’s doxxing.
He’s right, too: The US has twice enacted pDST - once during World War II, which ended after the war, and again in 1973 as an energy saving measure. Congress curtailed the experiment later in 1974 following public backlash over dark winter mornings.
The US isn’t alone in trying and failing at enacting pDST, either, as the Canadian paper points out. Russia adopted pDST in 2011 and reversed it in 2014. Chile tried and reversed it as well. In those cases, the reasons for reversing course varied, but concerns included dark winter mornings, disrupted sleep and body clocks, safety, and public dissatisfaction.
It’s unclear whether the US government’s latest attempt at enacting pDST will succeed despite political resistance and scientific evidence that it’s a bad idea, but the researchers sure seem to hope not: They note that, if the US makes such a change, Canada will likely be pressured to conform.
At the end of the day, we might all be better off just dealing with a couple of clock changes and some short-term sleep disruption. ®