Stanford researchers have found that ending the practice of switching clocks twice a year could significantly reduce rates of strokes and obesity across the U.S. Their analysis suggests that adopting permanent standard time would lead to greater health benefits than either permanent daylight saving time or continuing the seasonal clock changes.
By modeling exposure to light (sunrise and sunset), circadian rhythms, and health outcomes at the county level, the researchers estimated that permanent standard time could prevent about 300,000 strokes annually and reduce obesity in 2.6 million people. Permanent daylight saving time also helps, but less so—averting about two-thirds of those benefits.
The study emphasizes circadian burden, which refers to the strain on the body’s internal clock when daylight timing is misaligned with natural rhythms. Morning light plays a key role in keeping the body synced; evening light, especially when excessive, can delay or weaken this synchronization.
Results varied depending on geographical location and individual chronotype (whether someone is more of a “morning person” or “evening person”). While most would benefit most from permanent standard time, those who are naturally evening-oriented may fare better under permanent daylight saving time, because it shifts more light into the evening hours.
Though the modeling shows strong support for permanent standard time as the healthier policy, the authors note that their assumptions are idealized: they presume consistent light exposure before and after work, stable sleep schedules, and minimal indoor light pollution. Real-world behavior and environmental variables like weather and city infrastructure could alter outcomes.
In summary, Stanford’s work supports a strong case for reducing or eliminating seasonal clock changes in favor of a fixed time policy—especially permanent standard time—as a public health strategy.
