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Daylight Saving Time on the Brain

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Just as inexorably as spring follows winter, so do the complaints about daylight saving time seem to follow moving the clock ahead an hour. Does springing forward really mess up our brains as much as we might gripe about it on Monday morning?

We do influence our own bodies with our habits—as anyone who’s had a Saturday night ice-cream-and-feelings bender can tell you—so it’s not totally impossible that we might be able to influence our circadian rhythms with something like shifting our schedule forward or backwards. But can we actually rewind our internal clocks?

Daylight Saving Time and the Body Clock

One study in Western Australia—where citizens tried out daylight saving time from 2006 to 2009 before they voted not to keep it—tested this question by looking for daylight saving time effects on levels of cortisol, a hormone tied to sleep and stress. Researchers at Queen Elizabeth II Medical Centre examined cortisol levels in more than 27,500 Western Australians collected over a 13-year-period. The short answer: Certain watches in our bodies are going to keep on ticking away, no matter what.

“The essence of our paper was the importance of sunrise time as the primary factor regulating morning cortisol levels,” senior author David Henley wrote in an email. Henley and his team found that the time the sun rises, independent of clock time, “is the over-riding regulator” of this hormonal cycle, he says.

Henley says his findings don’t cast any judgment against or in favor of daylight saving time.

But the fact that we’re setting up a major discrepancy between our internal clock set by the sunrise and the one that tells us when we’re late for work or not seems like a troubling recipe. It does seem like something gets a bit out of whack once we start trying to grab extra light in the summer.

Sleeping Lessons

When daylight saving time’s not in effect, people’s sleep timing on “free days” (as in the weekend) follows the seasonal progression of sunrise, but during daylight saving time, it does not, according to one 2007 paper published in the journal Current Biology that drew on self-reported sleep data from 55,000 people.

On the other hand, perhaps some of us aren’t losing as much sleep as we think. In one study recently published in the Annals of Human Biology, researchers in Brazil asked 378 college students to keep a diary about when they went to sleep and when they woke up before and after the spring transition.

The scientists were interested in seeing if people with different sleep behaviors—preference for going to bed late or getting up early or somewhere in between—would adjust differently. But they found that both morning larks and night owls stayed in bed about the same amount in the week immediately after the transition as before, while intermediate types actually spent a little more time in bed after springing forward. (Then again, college students tend to have a little more flexibility in terms of bedtimes).

Sleep Loss Translates to Gains Elsewhere?

There’s also this to consider: The hardship of the initial transition into daylight saving time is a different question from weighing the pros and cons of daylight saving time in the long term. Maybe the annoying (sometimes occasionally health-threatening) consequences of springing forward are overpowered by greater gains throughout the season.

Studies in Germany and the United States find that the jump into daylight saving time is linked to increased traffic accidents right after the “spring forward,” probably thanks to sleepiness. However, a similar study in Sweden found little “measurable important immediate effects” from the daylight shift on crashes. And other research using U.S. traffic data has found [pdf] that having an extra hour of light in the evening seems to result in fewer fatal crashes throughout the entire period of daylight saving time.

Fallback Advice for Springing Forward

If you’re worried about getting thrown out of balance by the spring forward, you can probably make the transition easier for your body with a few simple actions. Getting light during your waking hours—and avoiding bright lights at night—helps you secrete melatonin, a hormone intimately tied to the sleep cycle. Other than that, exercising in the evening, avoiding alcohol and coffee right before going to bed, and trying to stick to a consistent bedtime are all more effective than cursing the alarm clock.

Image: Getty/Wataru Yanagida


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