Daylight saving haters rejoice: scientists confirm it’s bad for health

Daylight saving time is not just a hassle – it can also be bad for your health.

The twice-yearly “spring forward, fall back” routine rattles our bodies’ daily cycles, known as circadian rhythms, with potentially harmful consequences. And a new study supports what many sleep experts have long argued: the solution is getting rid of daylight saving for good.

That will not be easy. While there is plenty of support for eliminating the time change itself, Donald Trump and some in Congress have called for the opposite: making daylight saving permanent. And it may prove unpopular with those of us who enjoy an extra hour of light on a summer’s evening.

Illustration of woman charging her battery in her back at a wall outlet

Researchers at Stanford University found that keeping our clocks on standard time year round, instead of just in the autumn and winter (as in most US states as well as the UK), would reduce the prevalence of obesity and strokes. The study, published in the Proceedings of the National Academy of Sciences, stands apart from much other research thanks to its breadth. Instead of simply looking at what happens when the clocks change, the researchers compared three scenarios: permanent standard time, permanent daylight saving time, and the current switching system, which applies in most US states.

Dr Jamie Zeitzer, a professor of psychiatry and behavioral sciences, and Lara Weed, a PhD candidate in bioengineering, modeled sunlight exposure across every county in the 48 contiguous states, and compared that information with federal health data. The goal, Zeitzer says, was to use an existing mathematical model to discover the “circadian burden” of the three daylight scenarios – in other words, “how much stress are we putting on the circadian system?” That stress is associated with a variety of disorders, including obesity and stroke. The result suggested that, at least in circadian terms, permanent standard time is the least burdensome on our health.

“This goes along with what we’ve been saying since about 2019,” says Dr Karin Johnson, a neurology professor at the University of Massachusetts Chan school of medicine and a member of the American Academy of Sleep Medicine’s advocacy committee. Johnson testified in favor of permanent standard time in front of a US Senate committee in April, telling lawmakers it would create “a more natural alignment between our social schedules and the sun’s cycle every day of the year”.

“Our body rhythms basically get set by the sun,” she says. But because our natural cycle is slightly longer than 24 hours, “we need to get cues every day to stay on track. Otherwise, our rhythms get delayed.” That results in problems ranging from trouble sleeping and waking up to digestive issues. “The more we can stay aligned with the sun time,” she says, “the healthier it is for our body, the better our brain functions, the better our sleep.” The American Academy of Sleep Medicine (AASM), American Academy of Neurology and the health and safety-focused non-profit National Safety Council agree.