Research Shows Permanent Standard Time Is Healthier Than Daylight Saving Time
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STORY AT-A-GLANCE
Staying on permanent standard time instead of shifting clocks twice a year could prevent millions of cases of obesity and hundreds of thousands of strokes across the U.S.
Your circadian rhythm, your body’s internal clock, works best with early morning light, which helps regulate sleep, energy, metabolism, and immunity
Permanent daylight saving time still offers health benefits, but standard time provides stronger protection for the majority of people
Research shows only 15% of people, called morning larks, align better with daylight saving time, while the rest of the population benefits more from standard time
You can strengthen your circadian health by getting outside in the morning, limiting bright evening light, keeping your sleep schedule consistent, and supporting policies that keep clocks on standard time year-round
Every year, millions of Americans move their clocks forward in March and back in November, but the health toll of this routine is rarely considered. The disruption goes beyond grogginess — it unsettles your body’s internal clock in ways that ripple through sleep, metabolism, and cardiovascular health.
Losing alignment with your circadian rhythm doesn’t just leave you tired. It increases the likelihood of serious problems like obesity, heart disease, and stroke, conditions that damage quality of life and shorten lifespan. Even accidents and injuries rise in the days after clock changes, underscoring how deeply light and time shape human biology.
The debate over time policy has dragged on for decades, with arguments about energy savings, school safety, and leisure time. What’s been missing is hard data on long-term health effects. New research now offers that evidence, showing how the choice between daylight saving time, standard time, or biannual switching influences your body at the most basic level.1
The findings point to one simple truth: aligning your schedule with morning light supports a healthier rhythm, while shifting clocks away from that alignment carries measurable risks. This makes the discussion about time policy not just a matter of preference but one of public health.
Standard Time Reduces Obesity and Stroke Risk
For a study published in the Proceedings of the National Academy of Sciences, researchers used computer models that factored in the body’s internal clock to compare three scenarios: permanent standard time, which prioritizes more morning light, permanent daylight saving time, which shifts light later into the evening, and the current system of switching back and forth twice a year.2 Their goal was to see how each time policy affects health outcomes like obesity and stroke.
Findings showed clear benefits for standard time — The analysis revealed that permanent standard time produced the largest reduction in both obesity and stroke compared to the other policies. Specifically, the model estimated that obesity prevalence would drop by about 0.78%, which equals millions fewer Americans struggling with excess weight. Stroke rates also declined by about 0.09%, preventing hundreds of thousands of new cases each year.
Daylight saving time offered smaller benefits — Permanent daylight saving time also lowered risks but to a lesser extent. The decreases were about 0.51% for obesity and 0.07% for stroke. While still meaningful, these improvements fell short of the stronger impact predicted under standard time.
Circadian burden explained the differences — The study introduced the idea of “circadian burden,” meaning how hard your body’s internal clock has to work to stay aligned with the 24-hour day. Permanent standard time provided the lowest circadian burden, giving your body a healthier rhythm to follow. Less burden means your energy, metabolism, and immune system stay more synchronized, lowering risks of chronic conditions.
Geography influenced results — The benefits weren’t evenly distributed. People’s latitude and their position within a time zone shaped how much they gained from standard time. For example, those living on the western edges of a time zone experienced greater disruption under the current shifting system, so they stood to benefit the most when aligned with standard time.
Light exposure patterns drove the health improvements — Morning light helped speed up the circadian cycle to match the 24-hour day, while evening light slowed it down. Permanent standard time tilted light exposure toward the morning, which kept people’s biological clocks better synchronized. This alignment supported healthy weight regulation and lowered the risk of stroke by ensuring cardiovascular and metabolic systems worked more efficiently.
<label class="hide-text" contenteditable="false">Text within this block will maintain its original spacing when published</label>Your body relies on light cues to regulate hormones, energy production, and even immune function. When circadian burden increases — like it does during seasonal shifts — systems fall out of sync, leading to higher obesity and stroke rates. By reducing this burden, standard time created conditions for healthier cellular and metabolic function.
Morning Light Proves More Powerful Than Evening Light
In a related press release, Stanford Medicine researchers explained how their county-level modeling revealed the nationwide effects of staying on permanent standard time versus continuing to shift clocks.3 They emphasized that permanent standard time would prevent millions of health problems and argued that the U.S. has been making the “worst choice” by sticking with biannual shifts.
Researchers quantified the impact with striking numbers — The team estimated that permanent standard time would lead to 2.6 million fewer cases of obesity and 300,000 fewer strokes. Permanent daylight saving time also reduced cases, but only about two-thirds as much. This means that something as simple as choosing the right clock policy could determine whether your body stays in sync or struggles with excess weight and cardiovascular problems.
More morning light is protective — Lead researcher Jamie Zeitzer explained: “You generally
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