It happens every year around this period. Those clock faces with arrows on the TV news. The abrupt time change on the cable box and the cellphone. The more gradual changes as you try to remember to reset all the clock-like devices around the house. The forgotten alarm that goes off an hour earlier than you expected. And which button do you push to reset the dashboard clock in the car?

The annual springtime return to Daylight Time—which happens this year at 1 a.m. on Sunday, March 9—may seem to be just one more of those minor inconveniences of modern life.

But is it so minor? According to a recent study published in the New England Journal of Medicine, during the week after the shift into Daylight Time, the rate of hospital admissions for heart attack rose by as much as 10 percent. Another recent study compared high school students in parts of Indiana that use Daylight Time with those in other parts of the state that stay on Standard Time year-round. On average, those who were subjected to Daylight Time had SAT scores more than 16 points lower than those in areas that didn’t shift the clock!

Why? The simplest explanation is that the shift confuses the circadian clock in the brain. This inner clock relies on timed exposure to light, especially natural light, to keep itself in sync with the daily cycle of 24 hours. But the sun doesn’t “spring ahead” on March 9, and neither does your inner clock.

Let’s say your daily rhythm is going to sleep at 11 p.m. and waking up at 7 a.m.. If you live somewhere near the middle of the continental US, that means that during the first week of March, while you’re still on Standard Time, you wake up to find the sun is already up. So far, so good. But come Monday, March 10, when you get up as usual at 7 a.m., it’ll still be dark out for another half an hour or more. You’ve lost an hour of sleep, and your daily rhythm of energy and mood lags an hour behind where it usually is.

To adjust to this, you have to reset your inner clock. That means making a correction of a full hour, plus the daily correction of 20 minutes or so. Not so easy, especially when the morning light that helps you do it doesn’t show up until an hour later. Most of us need a week or more to adjust, and some researchers suggest that our clocks never fully adjust to Daylight Time.

The loss of an hour in March is hard on a lot of people. It is particularly hard on those who are battling winter depression. After March 9, according to the clock, sunrise will come as late as it did at the end of December, during the darkest days of the year. Sure, we also get an hour added on at the end of the day, but that’s no help. It is early morning light that our inner clocks rely on to keep in sync with the external world.

Can we do anything to make this transition easier? Well, yes, we can—but it means thinking ahead. The key is to be proactive. Make the adjustment ahead of time. Help the inner clock accommodate to the change gradually, before it happens. In a nutshell, that means waking up and turning up the lights 10 minutes earlier each day for the six days prior to the time change.

To make this still easier, go to Twitter (or @mychronotherapy if you’re already into tweets), sign up to follow us, and you’ll receive daily reminders throughout the week of March 2, 2014 on what to do for a smooth adjustment to Daylight Saving Time. The start date of the series was February 26, 2014, so look back to the introductory tweets.

Michael and Ian co-authored the 2013 Penguin paperback, Reset Your Inner Clock. They invite you to follow them on Twitter for news updates, opinions, and challenging Q-and-A’s. If you want to stay on top of body-clock matters, light therapy, and more — and take advantage of confidential, online self-assessments of inner clock time, depression, and seasonality — you should become part of the nonprofit Center for Environmental Therapeutics community. Email so we can stay in contact.

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