The chicken or the egg? Cats or dogs? What about pineapple on pizza?
There are many age-old debates that seem to stir a strong opinion from even the most non-confrontational people. Whether we should change the clocks isn’t as hotly debated, but if asked which way—daylight saving time or standard time—it’s likely even grandma will dig in on one side or the other.
Is one better, or worse, than the other? That’s exactly what Muzhe Yang, the MacFarlane Professor of Economics, and his co-authors Susan Averett, professor of economics at Lafayette College, and Laura Argys, professor of economics at the University of Colorado Denver, aimed to determine with their most recent research on how daylight saving time affects health and our circadian rhythm.
“Living in Sync with the Sun,” published in the American Journal of Health Economics, looked at those living close to a time zone border where solar time is similar, but clock time is different from solar time by up to an hour during standard time and sometimes even two hours during daylight saving time. Yang says their study differed from most in that the majority of research surrounding this topic is focused on short-term impacts of changing the clocks. Yang and his team studied the year-round effects of chronic circadian misalignment. Their research included comparing mental health outcomes for those on the eastern and western sides of a time zone border and found the worse outcomes for those on the east side of the border.
“Our study looks at a comparison between the two sides of a time zone border,” Yang says. “It is equivalent to estimating the health impact of moving a person from one side of the border to the other side. And it is essentially the comparison between choosing permanent daylight saving time, which is moving to the east side, and choosing permanent standard time, which is moving to the west side.”
Circadian misalignment, as described by Yang, is when the things we do each day, such as wake or eat, do not coincide with our body's natural rhythm. And that natural rhythm is largely determined by the sun, according to Yang.
Our body naturally follows what time the sun rises and sets, which is solar time, Yang says. Society, however, runs on clock time. The two being out of sync can negatively affect health over time. To have solar time and clock time line up perfectly, one would need the sun to be overhead at exactly noon. But with the Earth divided into 24 time zones, which is necessary to facilitate daily life as we know it, having the two times sync up only happens for a small amount of territory. Western (later) and eastern (earlier) sides of each time zone experience solar noon outside of noon on the clock.
The findings included a 6% increase in diagnosed cases of depression in those on the eastern side of time zone borders.
“That sounds small, but across millions of people, that will become meaningful, especially because depression is costly and deeply tied to quality of life,” Yang says. “This finding is also kind of striking if we consider the nature of the exposure examined by our study. It is not a sudden shock like a natural disaster. It is not an acute one-hour daylight saving time transition. It is a kind of subtle but persistent feature of our daily life.”
Yang had three main takeaways from the team’s research. First, the decision is both time policy and health policy—setting the clocks and outlining time zones affects both convenience and health. While Yang’s research finding supports standard time as being superior for our health, he acknowledges daylight saving time has its benefits. There’s more daylight in the evening, which can aid economic and recreational activities, and while evidence is mixed, it could result in energy savings. He summarizes daylight saving time benefits as more on the convenience and evening lifestyle side, which is where he feels the public debate often lies. Standard time benefits sleep and mental health, which he feels are often treated as secondary in the debate.
The second major finding in their research, Yang says, is that over time, small changes in circadian misalignment add up and can shift the population level risk in a measurable way. The focus is the one-hour clock shift in the spring or fall, but he says even slightly living out of sync with the sun for an extended period of time can have negative effects.
Yang says the team’s research shows him there are options—the decision does not have to be one that is all or nothing. An example he provides is adopting standard time to better align solar time with clock time but then encourage more flexible work schedules and consider redrawing time zone boundaries. In Europe, Yang said initiatives are already underway that would create time zones in which clock time never differs from solar time by more than 30 minutes.
“Even if there are benefits of daylight saving time, we should also consider what the net effect is once we factor in health,” Yang says. “Our paper adds evidence on that health side focusing on the impact of this year-round chronic misalignment that will be exacerbated when we permanently move our clock forward by one hour.”
