Twice a year, most of the country dutifully resets its clocks, and twice a year, plenty of people complain about it. What often gets lost in the debate over whether to keep switching, stick with daylight saving time year-round, or settle into permanent standard time is what the science actually says about which option is healthiest for the human body. According to sleep and circadian researchers, the answer is fairly clear, and it is not the option currently being pushed hardest in Washington.
How the Body’s Internal Clock Actually Works
Human beings, like most mammals, run on a roughly twenty-four-hour internal cycle called the circadian rhythm, which regulates sleep, appetite, mood, and a long list of other physiological processes. This internal clock depends heavily on light exposure, particularly natural sunlight, to stay properly synchronized with the outside world. When the timing of light exposure shifts, whether through jet lag, shift work, or a mandated change to the clock, the body’s internal rhythm can fall out of alignment with its environment, a condition researchers sometimes describe as social jet lag.
Why Standard Time Aligns Better With Human Biology
The core argument for standard time comes down to when daylight actually reaches us during the day. Standard time places more natural light in the morning hours, which research shows is particularly important for keeping the circadian clock properly set. Morning light exposure helps signal to the brain that the day has begun, supporting more consistent sleep and wake timing. Daylight saving time, by contrast, shifts more light toward the evening, delaying that morning light signal and pushing the body’s natural rhythms later, which tends to make it harder to fall asleep at a reasonable hour and harder to wake up feeling rested the next morning.
A Major New Study on Long-Term Health Effects
A study published in 2025 by Stanford Medicine researchers modeled how three different time policies, permanent standard time, permanent daylight saving time, and the current twice-yearly switching, would affect circadian health and long-term disease risk across the country. The researchers found that continuing to switch the clocks twice a year is, from a circadian health standpoint, the worst option of the three. Both permanent alternatives would be healthier than the current system, but permanent standard time offered the larger benefit. According to the study’s modeling, adopting permanent standard time nationwide could prevent roughly three hundred thousand strokes and result in about two point six million fewer cases of obesity annually, compared to about two thirds of that benefit under permanent daylight saving time.
Why the Twice-Yearly Switch Is Especially Harmful
Beyond the long-term risks tied to which permanent time policy is chosen, the act of switching itself carries well-documented short-term dangers. The sudden loss of an hour of sleep each spring has been linked to measurable increases in heart attacks and fatal traffic accidents in the days immediately following the change. Because the body’s circadian rhythm cannot instantly adjust to a sudden one-hour shift, the days surrounding each time change tend to bring a temporary but real spike in health and safety risks, on top of the more gradual, longer-term effects tied to whichever permanent policy is ultimately in place.
What Major Medical Organizations Recommend
The scientific and medical community has largely converged on the same recommendation. The American Academy of Sleep Medicine formally supports eliminating seasonal time changes in favor of permanent standard time, stating that this option aligns best with human circadian biology and offers the greatest potential benefit for public health and safety. That position has been echoed by other organizations, including the Sleep Research Society, the National Sleep Foundation, the Society for Research on Biological Rhythms, and the American Medical Association, all of which have issued similar statements favoring permanent standard time over permanent daylight saving time.
Public Opinion Has Shifted as Well
Public sentiment around daylight saving time has changed noticeably in recent years. A 2025 Gallup poll found that a majority of Americans now oppose daylight saving time altogether, a sharp decline in support compared to surveys conducted decades earlier. Among those surveyed, close to half expressed a preference for permanent standard time, while a smaller share favored permanent daylight saving time, and an even smaller group preferred keeping the current twice-yearly system in place.
Where Current Legislation Stands
Despite the weight of scientific opinion favoring permanent standard time, recent legislative efforts have moved in the opposite direction. As of mid 2026, the United States House of Representatives has passed legislation that would make daylight saving time permanent nationwide, though the bill still needs to pass the Senate and be signed into law before taking effect. Sleep medicine organizations have continued to recommend permanent standard time as the healthier long-term option even as this legislation moves through Congress, highlighting an ongoing gap between the policy path being pursued and the guidance coming from the scientific community most focused on circadian health.
What This Means for You Right Now
While the broader policy debate continues, there are still some practical takeaways for individuals. Prioritizing consistent sleep and wake times, seeking out natural morning light exposure when possible, and being especially mindful of extra rest in the days surrounding each seasonal clock change can help reduce the personal impact of whatever time policy happens to be in place. Understanding why standard time tends to feel more aligned with the body’s natural rhythms can also help make sense of why the spring shift to daylight saving time often feels noticeably harder on sleep and mood than the fall shift back to standard time.
Final Thoughts
The scientific consensus on this question has become increasingly clear over the past several years. Permanent standard time aligns more closely with human circadian biology than permanent daylight saving time, and both permanent options are considered healthier than continuing to switch the clocks twice a year. As lawmakers continue debating which path to take, the recommendation from sleep and circadian researchers remains consistent, favoring the version of time that keeps more daylight in our mornings rather than our evenings.
