Ending the twice-yearly ritual of changing clocks could prevent 300,000 strokes and 2.6 million cases of obesity annually across the United States, according to new research from Stanford Medicine.
The study, published in the Proceedings of the National Academy of Sciences, compared three time policies and found that maintaining permanent standard time—essentially staying on “winter time” year-round—offers the greatest health benefits.
“Staying in standard time or staying in daylight saving time is definitely better than switching twice a year,” senior study author Jamie Zeitzer, professor of psychiatry and behavioral sciences at Stanford University, said in a statement.
Not Changing Time Is Healthier
The team found that, from a biological perspective, adhering to either standard time or daylight saving time year-round would be better for health than switching twice a year, with permanent standard time offering the most benefit.
The research team used mathematical models to analyze how different time policies—such as daylight saving, standard time, or changing time scheduling—affect the body’s circadian rhythm due to varying sunlight exposures.
Researchers then predicted health outcomes based on these different time conventions after taking into account current obesity and stroke rates.
Their findings suggest that maintaining a permanent standard time could lower obesity prevalence by 0.78 percent and stroke rates by 0.09 percent—translating to 2.6 million fewer obesity cases and 300,000 fewer strokes nationwide. Permanent daylight saving time would achieve roughly two-thirds of those benefits.
The key lies in morning light exposure.
“Light triggers certain brain regions to prepare us for the day’s challenges,” Dr. Stephen Carstensen of Seattle Sleep, who was not involved in the study, told The Epoch Times.
Zeitzer said in the statement that the human circadian cycle naturally runs slightly longer than 24 hours.
When you get light in the morning, it speeds up the circadian cycle to promote wakefulness, and the darkness at night stimulates melatonin, which prepares you for sleep.
Most people would benefit from staying on standard time, as it is aligned with the sun, allowing them more light in the mornings. Daylight saving time, on the other hand, is one hour ahead, and therefore makes people out of sync with the sun.
The Fatigue Factor
The dangers of sleep disruption extend far beyond individual health. Historical disasters, including the 1986 Challenger explosion and 1989 Exxon Valdez oil spill, have been linked to fatigue-impaired decision-making, highlighting how sleep deprivation can have catastrophic consequences.
While these incidents weren’t directly caused by daylight saving time, they underscore the broader risks of disrupted sleep patterns—risks that affect millions of Americans twice yearly during time transitions.
“Whenever we try to work against what is naturally evolved, it causes disturbances to homeostasis, our body’s drive to return to normal,” Carstensen said.
Growing Momentum for Change
There is already widespread support for ending the biannual time changes. Several states have passed legislation to eliminate seasonal time changes, contingent on federal approval. Additionally, a 2023 survey from the American Academy of Sleep Medicine found that 64 percent of U.S. adults support eliminating seasonal time changes.
Proponents of permanent standard time, including the American Academy of Sleep Medicine and the American Medical Association, believe that more morning light is better for overall health.
“The problem is that it’s a theory without any data. And finally, we have data,” Zeitzer said in the statement.
Legislation proposing permanent daylight saving time has been introduced in Congress repeatedly since 2018, but it has yet to pass.
Supporters of permanent daylight saving time argue that more evening light can save energy, reduce crime, and provide more leisure time.
The findings suggest that most people would experience the least circadian disruption under permanent standard time as compared to daylight saving time.
Despite the benefits, the study acknowledges several limitations, including assumptions about consistent daily light habits that may not accurately reflect real-world behavior. “People’s light habits are probably much worse than what we assume in the models,” Zeitzer said in the statement.
The study notes that the current system of seasonal clock changes is not ideal, but also recognizes that other factors, such as geography and weather, influence light exposure and circadian health.
“No policy will add light to the dark winter months,” Zeitzer stated. “That’s the sun and the position of Earth. We can’t do anything about that.”
Adapting to Time Changes
For those dealing with current time transitions, sleep experts recommend practical steps to minimize disruption.
Dr. Michael Aziz, an attending physician at Lenox Hill Hospital in New York, who was not involved in the study, told The Epoch Times that time changes frequently disrupt sleep—but following a few simple steps can significantly minimize the impact.
Steps include gradually shifting your sleep schedule by adjusting your bedtime by 15 minutes each night, either earlier or later, depending on whether the change is to standard or daylight saving time in the week prior. “This eases the body into the new schedule,” Aziz said.
He also recommends using light to reset our internal clock after a time change.
“Light exposure is a strong signal for regulating your circadian rhythm,” he said. “So in the morning, get bright light exposure as soon as you wake up by opening curtains, going for a walk, sitting on a porch, or by looking out of a window.” He said that exposure to natural light helps suppress melatonin and signals the body that it’s daytime.
“In the evening, reduce your exposure to blue light coming out of computers, iPads, and TVs. Dim the lights to help signal that it’s time to wind down.”