Hate daylight saving time? New Stanford study says it could seriously harm your health

Do you dread springing forward or falling back for daylight saving time (DST)? Every spring and fall, many of us groan when it's time to shift the clocks: lose an hour, gain an hour, mess with our sleep. It feels annoying, sometimes weird, but it turns out it may be more than just a bug in the calendar.A new Stanford study suggests the twice-annual shift of daylight saving time not only disrupts our mood and schedules, but it could harm our health in lasting ways, by subtly increasing our risk of obesity, stroke, and other chronic health issues.In fact, the researchers argue that sticking with permanent standard time (no spring-forward, no fall-back) might be the healthier option.Want more insight? Read on.A study by Stanford Medicine, published September 15, in Proceedings of the National Academy of Sciences, argues that the twice-annual shift of clocks for DST causes harm over time and that adopting permanent standard time could help people be healthier.Using advanced modelling, the researchers compared three time policies:Current system: switching clocks twice per year (standard time into daylight saving time).Permanent daylight saving time: staying on DST year-round.Permanent standard time: staying on standard time year-round.They used county-level data across the United States, light exposure models, sunrise/sunset times, and health statistics from the Centers for Disease Control and Prevention (CDC).What did the Stanford study find?Permanent standard time would lead to the lowest “circadian burden,” meaning your internal clock would need to adjust less often to stay in sync with daylight. That helps reduce stress on the body.Under permanent standard time, the models estimate about 2.6 million fewer people in the US would have obesity, and approximately 300,000 fewer stroke cases per year, compared to continuing the clock changes.Permanent daylight saving time also shows benefits, but much less than standard time. For example, obesity might still drop by roughly 2.6 million people, and strokes by about 220,000, under the DST-year-round scenario.A big part of the problem is circadian rhythm, our body’s internal clock that regulates sleep, metabolism, hormone release, immune function, and more. It depends on light cues, especially morning light, to reset each day. When clocks shift or when mornings are dark, this rhythm is disrupted.The study also shows that moving to permanent standard time means more exposure to morning sun, which helps align the circadian rhythm properly. More evening light (as in permanent daylight saving time) helps some people, especially night-owls, but overall is not as helpful for many. Obesity: Disrupted circadian rhythms are linked with weight gain – less regulated hormones, poorer sleep, and disturbed metabolism. A more stable light-dark cycle helps with better sleep, more consistent routines, and potentially better weight control.Stroke risk: Sleep disruption, misalignment of internal clocks, possibly more stress on blood vessels – all may contribute to higher stroke risk when clock changes misalign our biological timing.Also, previous research has connected the clock shifts with more heart attacks, traffic accidents, lower alertness, reduced productivity, and mood disturbances. The new study adds long-term modeling to show that this isn’t just acute effects, but chronic population-level effects.What could happen if we discard the shifting of time twice a year? The probable outcomes are just modeled estimates. They assume certain behaviors: regular sleep windows, people spending time outdoors exposed to natural light, etc. Real life may differ (night shift workers, people in apartments, varied schedules).As always, there are trade-offs. Some people want longer evenings (more daylight after work), which permanent DST offers. But those gains may come at the cost of more dark mornings, which seems worse for circadian health.Policymakers might use these findings to push for laws making standard time permanent. Some states have already proposed or passed resolutions. Individual people can try to protect their schedules: aim for consistent sleep and wake times; get morning sunlight exposure; limit bright light in the evening; minimize sudden disruptions.Moreover, it is recommended to watch for public health messaging, because changes in time policy may affect energy usage, safety (e.g., darkness for school kids), commerce, and daily routines, so any shift needs careful planning.