To help your body adjust to daylight saving time, try sunlight and exercise

How to Switch to Daylight Saving Time Without Leaving Your Body and Brain Behind

By Matt Fuchs edited by Tanya Lewis

On Sunday at 2 a.m. local time, Daylight Saving Time will begin in most US states and clocks there will move forward one hour. Research shows that hospital admissions increase just after this annual clock change and many people lose sleep for a week or more. The time change can also worsen sleep problems and depression.

But researchers have identified two behaviors that, combined in the morning, can stabilize circadian rhythms and ease the transition.

Daylight, absorbed by the eyes early in the morning, activates a pair of pea-sized clusters of cells located deep in the brain called the suprachiasmatic nucleus, or SCN. The SCN’s tiny dimensions belie its importance as the body’s primary alarm clock. It sends rhythmic signals to millions of other timers, called peripheral clocks, located in almost every cell with a nucleus in the body. These cells, in turn, activate genes that prepare our organs for the actions of the day, such as eating and digesting food.

On supporting science journalism

If you enjoy this article, please consider supporting our award-winning journalism by subscription. By purchasing a subscription, you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.

The light-triggered SCN has been called the body’s “master” clock. But recent research shows that light is just one of many factors that determine our internal perception of time; another is exercise. Karyn Esser, a physiologist at the University of Florida, and colleagues found that exercise performed early in the morning is a powerful signal to the body’s peripheral clocks in oxygen-sensing organs such as muscles. And other researchers have made similar findings in studies of the lungs and kidneys. “Healthy circadian rhythms require coordination of clock systems throughout the body,” explains Esser.

Since light and exercise influence circadian rhythms separately through the SCN and peripheral clocks, respectively, scientists believe that the combination of these cues—exercise and morning sunlight—might work better to shift internal clocks to the time of both cues than light or exercise alone.

Shawn Youngstedt, a professor of exercise science at Arizona State University’s Edson College, and colleagues tested this combination on a small sample of adults. Researchers found that this produced a greater change in the timing of the internal clock than simple exercise or exposure to light (bright enough to simulate sunlight). This combination still needs to be tested in larger studies, Youngstedt says, but exercise “has a significant impact” on the body’s ability to adapt to time differences.

And scientists know that strong dawn triggers help ensure smooth dusk. Circadian clocks, once activated, begin a precise countdown to the release of melatonin that evening, the hormone that lulls us into a state of relaxation and preparation for sleep.

Exercise and daylight exposure may be synergistic in other ways: Exercise causes our eyes’ pupils to dilate and capture more light, which could be particularly helpful when eyes lose sensitivity to light as people age.

Modern schedules and artificial light often interfere with individuals’ 24-hour biological cycles. Regular disruption of these cycles, or circadian rhythms, is linked to chronic disease and premature death.

The loss of an hour when the clocks move forward on March 8 may seem insignificant, but the sudden shift between our internal and external clocks can compromise sleep, well-being, road safety and heart health.

To manage these risks, experts suggest preparing for the transition a few days in advance using the light and locomotion strategy. Wake up 15 to 20 minutes earlier each day from March 5 to 8 and take an outdoor walk or jog an hour after you wake up (indoor light is usually not bright enough to reset internal clocks). These gradual changes will gradually acclimate your body to the clock change.

The more body parts you exercise, the better, says Esser. She suggests that you try to get out of breath a little by exercising at about 50 to 75 percent of your full effort.

This preparation is especially important for the elderly or those suffering from chronic illnesses. Around age 40, circadian rhythms begin to lose flexibility, leading to “longer clock shift adjustments and a higher likelihood of problems,” says Esser.

Certain habits could cancel out the advantages of the light and locomotion strategy. Eating late at night or bright light later in the day can change rhythms later, just as mornings get brighter earlier, says Gad Asher, a biochemist at the Weizmann Institute of Science in Rehovot, Israel, who studies the body’s internal clocks.

After you’ve established an earlier, stronger circadian rhythm—and emerged unscathed—don’t throw away your new light and exercise habit, says Asher. Keep your pace stable to maintain your health in the long term. “What really matters is your daily habits,” he says.

It’s time to defend science

If you enjoyed this article, I would like to ask for your support. Scientific American has been defending science and industry for 180 years, and we are currently experiencing perhaps the most critical moment in these two centuries of history.

I was a Scientific American subscriber since the age of 12, and it helped shape the way I see the world. SciAm always educates and delights me, and inspires a sense of respect for our vast and magnificent universe. I hope this is the case for you too.

If you subscribe to Scientific Americanyou help ensure our coverage centers on meaningful research and discoveries; that we have the resources to account for decisions that threaten laboratories across the United States; and that we support budding and working scientists at a time when the value of science itself too often goes unrecognized.

In exchange, you receive essential information, captivating podcasts, brilliant infographics, newsletters not to be missed, unmissable videos, stimulating games and the best writings and reports from the scientific world. You can even offer a subscription to someone.

There has never been a more important time for us to stand up and show why science matters. I hope you will support us in this mission.