The Health Risks of Permanent Daylight Saving Time
Why the rare bipartisan support for permanent DST gets the science wrong.
Posted May 26, 2026 | Reviewed by Lybi Ma
In a Washington climate defined by gridlock and deeply partisan politics , something remarkable is happening. Congress is on the verge of passing the Sunshine Protection Act, a law that would make daylight saving time permanent, with robust bipartisan support and a firm endorsement from the administration.
Why are sleep scientists pushing back against this unusual moment of political harmony?
Sleep scientists broadly agree with the overall premise behind the bill, that the twice-yearly clock change is inconvenient and, at least, acutely harmful. Each March, in the week following the clock change where we spring forward , we see a measurable spike in car crashes, heart attacks, and workplace injuries, all driven by the acute sleep loss of a single hour. Ending that biannual disruption is a legitimate public health goal. However, the disagreement lies in which permanent time to choose. Congress wants to lock in daylight saving time, and they frequently cite evidence that permanent daylight saving time is good for public health. But actually, the science supports the opposite: Permanent standard time. That distinction matters far more than most people realize.
Five Myths Driving the Wrong Decision
Myth 1: Permanent DST means more sunlight. It does not. The length of the day is determined by the Earth's orbit, not our clocks. Daylight saving time shifts one hour of morning sunlight into the evening. That sounds appealing on the face of it, but morning light is not interchangeable with evening light. Morning sunlight is among the most powerful biological signals we have for anchoring the body's internal clock and regulating mood, alertness, and sleep quality. Moving it to evenings carries real costs that don't show up in political talking points.
Myth 2: Permanent DST will make roads safer.
The evidence is more complicated than advocates suggest. Darkness does increase crash risk, but the relevant question is whether brighter evenings will offset the danger of dark morning commutes, when adults are driving to work, teenagers are driving to school, and children are walking to school or to the bus.
Myth 3: Making DST permanent solves the "spring forward" problem.
The United States already ran this experiment. In the early 1970s, Congress passed permanent year-round DST as a response to the energy crisis. It was repealed within a year. The public backlash was intense: people were commuting and sending children to school in the dark, morning crash rates climbed, and the promised energy savings never materialized. This is not a theoretical concern. We have lived data, and it did not go well.
Myth 4: People will be more productive and happier.
Here’s where they really get it wrong. As humans, we are creatures of the light. Our circadian rhythms , which govern our sleep, our mood, our alertness levels, and many other critical physiological functions, are regulated by exposure to light. Permanent DST shifts light exposure, such that we will have less morning light exposure and more evening light. Reduced morning light exposure is directly linked to elevated rates of depression and other mood disorders, whereas increased light exposure at night is linked with difficulty falling asleep and shorter sleep duration. This is concerning for everyone, but especially for teenagers, a population the U.S. Surgeon General has described as being in a mental health crisis and who are among the most vulnerable to insufficient sleep. A teen who currently wakes at 6:30 a.m. for school would, under permanent DST, effectively be rising at 5:30 a.m., which is in the middle of their biological night. That is not a minor inconvenience. It is a chronic health stressor with documented consequences.
Myth 5: Bodies will eventually adjust.
Human circadian rhythms are not arbitrary. They are biological clocks shaped over millennia to track the natural light-dark cycle, and they run on solar time, not legislative time. Locking in DST means most people would chronically wake before sunrise to meet work and school demands, creating a lasting mismatch between their internal biology and the external world. Sleep scientists call this social jetlag. Its health consequences, including metabolic disruption, mood disorders, impaired cognition , and cardiovascular strain, are well documented. No amount of time on a new schedule resolves it.
The Right Answer Is Already on the Table
If the goal is to eliminate the wildly unpopular biannual clock shift, then the evidence-based solution is permanent standard time. This is what the evidence supports. Standard time aligns most closely with the natural solar cycle and with human circadian biology, which is exactly why professional sleep societies have recommended it consistently and clearly.
Congress has a genuine opportunity to work together to improve public health. The instinct to stop changing the clocks is supported by the public and by science. The direction of the fix is not science-backed.
Sleep is a biological necessity. Policy should treat it like one.
https://aasm.org/aasm-statement-senate-daylight-saving-time-sunshine-pr…
https://pubmed.ncbi.nlm.nih.gov/10381883/
https://www.washingtonpost.com/history/2022/03/18/daylight-saving-seven…
https://thehill.com/policy/5889199-permanent-daylight-saving-time-legis…
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Wendy Troxel, Ph.D., is a Senior Behavioral Scientist at the nonprofit, nonpartisan, RAND Corporation, and licensed clinical psychologist. She is internationally recognized as the leading authority on couples and sleep and author of Sharing the Covers: Every Couple’s Guide to Better Sleep.
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