There is a growing backlash against the back-and-forth time changes that happen every year in the U.S. and elsewhere, when we switch into Daylight Saving Time and then back out again. The idea of staying in one “time” has become popular enough that several states in the U.S., including California, Washington, Florida, and North Carolina, are now considering doing away with the practice by making daylight savings time (DST) permanent. But, there may be an unintended consequence to that move.
At the same time that this move to cancel DST is going on, more and more schools across the country are moving their high school start times later, because of new information about how adolescent body clocks work.
However, new research shows these two moves may cancel each other out. British scientists looking into the matter say permanent DST would make it harder to wake up in the winter, as it would remain dark an hour later into the morning, therefore undermining efforts in many states to give teens more time to sleep.
“There has been a long-term, very active debate in the U.S. and other countries on the difficulties teenagers have in getting up for school,” said Anne Skeldon, Professor of Mathematics at the University of Surrey. “Similar discussions on school start times and on permanent daylight saving/standard time are happening in Europe. It seemed important to us to point out that moving to permanent daylight saving will undermine any benefits on sleep timing of shifting school start time later.”
Thinking through why permanent DST would negate changes in school start times is a bit tricky, Skeldon explained. That’s because it requires understanding how three different times are related to each other and how they shift over the course of the year: environmental time as determined by the sun, our internal biological time (linked to actual light exposure, including sunlight), and the time that we set on our clocks.
If the clocks weren’t turned back in the fall, as under permanent DST, it would mean that sunrise would come at an even later clock time than it already does during those shorter days of the winter. As a result, Skeldon and co-author Derk-Jan Dijk, Professor of Sleep and Physiology and Director of the Surrey Sleep Research Centre, write, “a required wake time of 7 a.m. during DST leads to the same degree of misalignment [between the socially required wake time and biological wake time] as a required wake time of 6 a.m. during ST. With permanent DST, schools would need to delay start times by one hour during the winter months just to maintain the status quo!”
Of course, they continued, it’s possible that people living indoors under electrical lighting aren’t affected that much by shifts in sunrise. But, if that’s true, they point out, then it really doesn’t matter what time school starts in the first place.
To sort it out, more research is needed to understand how light exposure affects the sleep and biological clocks of people living in different environments.
“We know that spending most of our lives inside and having the lights on late into the evening has had profound effects on when we sleep, but we still have much to learn about exactly how much this matters,” Skeldon says.
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