There are the signs that fall is in full swing — knits, pumpkin spice everything, and the turning back of the clocks.
The U.S. is one of about 70 countries worldwide that have adopted daylight saving time; the rest mainly exist in Europe. This means that unless you live in (most of) Arizona, Hawaii, or one of the territories, you “lose” an hour in the spring and vice versa in the fall.
Despite the widespread adoption of daylight saving time, research has linked the jump forward in springtime to a decrease in sleep, vigilance, and engagement at work. More seriously, the second Sunday in March sees a spike in the number of heart attacks and fatal traffic accidents.
Now, researchers writing in the Proceedings of the National Academy of Sciences have identified longer-term health implications.
Read More: Year-Round Daylight Savings Could Threaten Our Sleep and Heart Health
Health Conditions and Daylight Saving Time
The team looked at three different time policies — permanent standard time, permanent daylight saving time, and the current model, biannual shifting (BAS) — and analyzed their impact on an individual’s circadian rhythm using a mathematical model. More specifically, they considered the circadian burden, which is the amount a person’s internal body clock (aka their circadian rhythm) has to adjust to maintain the 24-hour day, using core body temperature as a phasemarker.
The timings of sunrise and sunset varied. More western counties experienced later sunrises and sunsets than more eastern counties in their respective time zones, while those further north experienced shorter days in the winter and longer days in the summer. To ensure a fair comparison, the “individual” simulated across counties and time policies maintained a rigid sleep pattern (10 p.m. to 7 a.m.) and a fixed work schedule (9 a.m. to 5 p.m.).
The researchers then compared the results to county-level data on the prevalence of health conditions such as cancer, depression, obesity, and stroke, which had been collected by the Centers for Disease Control and Prevention (CDC).
Circadian Rhythm and Burden
When it comes to BAC’s impact on an individual’s circadian burden, the results suggest it varies not only by location but by whether you identify as a morning lark or night owl.
Each of us possesses a unique chronotype that determines when we feel our most alert. Most fall into the “intermediate” group, with a circadian cycle just a little bit longer than the 24-hour day.
However, 15 percent of the population identifying as “morning larks” have a naturally shorter circadian cycle. Because more evening light extends their cycle closer to the 24-hour ideal, they experience the lowest circadian burden when the clocks change. Other chronotypes feel the impacts of BAC to a greater extent, along with those living further west in their time zone.
This could be a problem because having a circadian rhythm that is out of sync can cause significant health problems. According to the researchers, switching to permanent standard time could lead to a decrease in obesity by 0.78 percent and stroke by 0.09 percent. That equates to 2.6 million fewer people with obesity and 300,000 fewer strokes.
Meanwhile, converting to permanent daylight savings would result in 1.7 million fewer people with obesity and 220,000 fewer strokes.
What the Future Holds
This is just part of the story. While the research accommodates differences in light exposure, it doesn’t take into account differences in weather or the chaotic, idiosyncratic intricacies of human behaviour. In reality, the average person does not maintain as unyielding a schedule as the individual in the simulation and probably sleeps quite a bit less.
However, it does lend more credence to proposals to switch to permanent standard time — a policy already endorsed by institutions like the American Medical Association and frequently (but so far unsuccessfully) attempted by Congress.
Read More: Here’s How Daylight Saving Time Influences Wildlife
Article Sources
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