The start of Daylight Saving Time is just on the horizon, along with our annual panic over which clocks switch automatically and which are manual (how much do you know, microwave?). But beyond that low-level stress, it turns out Daylight Saving Time can impact our health in both positive and negative ways.

Falling Back

The extra hour of sleep we get when Daylight Saving Time ends in the fall is a major boon for our chronically sleep-deprived society, says Wayne Andersen, M.D., co-founder and medical director of Take Shape For Life.

But it's only great if you can actually sleep that extra hour. Those of us with less-than-stellar sleep habits (like taking long late-afternoon naps or scrolling through Instagram in bed) won't reap the same benefits, says Teofilo L. Lee-Chiong, Jr., M.D., a sleep expert and professor of medicine at the University of Denver. "In fact, many people don’t—or can’t—take advantage of the extra hour due to the body’s circadian clock, and may wake up earlier than usual," Lee-Chiong says.

If you're one of those people, you can blame the suprachiasmatic nucleus (SCN), which acts as our central clock and regulates our body temperature, digestion, hormone release, and sleep-wake cycles. The SCN is programmed to work around daylight, so when we try and artificially override it, we're not always successful.

Falling back also coincides with winter's shorter days, which can lead to an uptick in the number of people who suffer from seasonal affective disorder (SAD), Andersen says. "Research has shown that people with SAD feel better after exposure to bright light and greatly benefit from sunlight in the morning," Lee-Chiong says. "So during the fall and winter months, when we get less exposure to sunlight, it can be helpful for people with SAD to counteract the effects of lost sunlight with bright artificial light therapy."

Springing Forward

We're big fans of sleep (us and the rest of the world), so we've always struggled to see the benefits of losing an hour in early March. But the added sunlight does have its perks. "If there are more daylight hours, people are more likely to be out and moving around more, so their fitness levels may actually be enhanced," Andersen says.

The switch, however, comes at a cost. Studies have shown that losing an hour of sleep makes people tired and stressed out, which leads to a 24 percent increase in the number of heart attacks the Monday after Daylight Savings Time starts.Daylight savings time and myocardial infarction. Sandhu A, Seth M, Gurm HS. Open heart, 2014, Mar.;1(1):2053-3624. Daylight saving time shifts and incidence of acute myocardial infarction--Swedish Register of Information and Knowledge About Swedish Heart Intensive Care Admissions (RIKS-HIA). Janszky I, Ahnve S, Ljung R. Sleep medicine, 2012, Jan.;13(3):1878-5506. And with more tired people, there are more car accidents on the road and decreased concentration and productivity at the office—a phenomeon aptly named "cyberloafing."The effects of daylight and daylight saving time on US pedestrian fatalities and motor vehicle occupant fatalities. Coate D, Markowitz S. Accident; analysis and prevention, 2004, Jul.;36(3):0001-4575.
Lost sleep and cyberloafing: Evidence from the laboratory and a daylight saving time quasi-experiment. Wagner DT, Barnes CM, Lim VK. The Journal of applied psychology, 2012, Feb.;97(5):1939-1854.

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The Takeaway

As with most things, Daylight Saving Time comes with benefits and drawbacks. Falling back can mean an extra hour of blissful sleep—if you can actually get the shut-eye. But it also means saying hello to darkness, our old friend, which can cut down our Vitamin D levels and usher in the season of SAD.

Come spring, losing an hour is hard on everyone. With one less hour of sleep, your body has less time to deal with stress and all of its implications.Associations between sleep and cortisol responses to stress in children and adolescents: a pilot study. Capaldi Ii VF, Handwerger K, Richardson E. Behavioral sleep medicine, 2006, Feb.;3(4):1540-2002. But with more daylight hours comes more time for physical activity and its health benefits (again, if you take advantage of it).

In general, it's not easy to hit reset on your circadian rhythm—or your microwave (but that's slightly less important).

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