A study from Stanford Medicine suggests that switching to permanent standard time could significantly improve public health, potentially preventing 300,000 strokes and reducing obesity by 2.6 million cases each year.
Americans have long participated in the biannual ritual of adjusting their clocks for daylight saving time, yet few express much joy about it. The time shifts in March and November, while inconvenient, have also been linked to a variety of health issues, including increased rates of heart attacks and fatal traffic accidents in the days following the changes.
Now, new research from Stanford Medicine highlights even more extensive health ramifications and recommends an alternative approach.
The study, published today in the Proceedings of the National Academy of Sciences, explores how three different time policies — permanent standard time, permanent daylight saving time and the current biannual shifting — impact people’s circadian rhythms and overall health. Circadian rhythms, the body’s natural 24-hour clock, regulate various physiological processes essential for optimum health.
The team concluded that both permanent standard time and permanent daylight saving time are healthier than the current system of switching twice a year. Permanent standard time, however, emerged as the best option, benefiting a broader segment of the population.
“We found that staying in standard time or staying in daylight saving time is definitely better than switching twice a year,” senior author Jamie Zeitzer, a professor of psychiatry and behavioral sciences, said in a news release.
Lara Weed, a graduate student in bioengineering, is the lead author of the study.
By employing a mathematical model to assess light exposure and its effects on circadian rhythms, the researchers predicted that permanent standard time could prevent around 300,000 strokes annually and reduce the number of obese individuals by 2.6 million.
The findings hold significant implications in the debate over time policy.
Some advocate for permanent daylight saving time, citing benefits such as energy savings and enhanced leisure time.
Others argue for permanent standard time, stressing the health advantages of early morning light. For instance, organizations including the American Academy of Sleep Medicine and the National Sleep Foundation endorse year-round standard time.
“It’s based on the theory that early morning light is better for our overall health,” Zeitzer said of the latter endorsements, adding, “The problem is that it’s a theory without any data. And finally, we have data.”
Human circadian cycles are slightly longer than 24 hours for most individuals but can be modulated with light exposure. Morning light helps speed up the circadian clock, while evening light slows it down. A well-synchronized circadian cycle is important for health, influencing various bodily functions such as the immune system and energy levels.
“The more light exposure you get at the wrong times, the weaker the circadian clock,” Zeitzer explained.
Importantly, the benefits of permanent standard time are not uniform across the population. Morning larks — people who prefer early mornings — constitute 15% of the population and would experience the least circadian burden under permanent daylight saving time because it extends their natural circadian cycle.
To link circadian burden with specific health outcomes, the researchers analyzed CDC data on the prevalence of arthritis, cancer, chronic obstructive pulmonary disease, coronary heart disease, depression, diabetes, obesity and stroke.
They predicted that several health conditions, particularly those influenced by circadian rhythms, would improve significantly under permanent standard time compared to biannual time shifts.
However, Zeitzer emphasized that this study is only a starting point. Future research should incorporate influences such as weather, geography and human behavior. Real-world light habits, often less ideal than modeled assumptions, could affect the findings significantly.
“People’s light habits are probably much worse than what we assume in the models,” added Zeitzer. “Even in California, where the weather is great, people spend less than 5% of their day outside.”
While the study presents a compelling case for permanent standard time, Zeitzer acknowledges that other considerations, such as economic and sociological impacts, must also be evaluated. Ultimately, the choice of time policy revolves around the arbitrary selection of clock hours, which cannot alter the inherent challenges posed by seasonal variations in daylight.
Source: Stanford Medicine