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.
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.
Their goal was to see how each time policy affects health outcomes like obesity and stroke.