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

How to “spring forward” for daylight saving time without leaving your body and brain

By Matt Fuchs edited by Tanya Lewis

On Sunday at 2:00 a.m. local time, daylight saving time will begin in most US states, and clocks will jump forward one hour. Research shows that hospital admissions increase immediately after this annual clock change, and many lose sleep for a week or longer. The time change can also worsen sleep disorders and depression.

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

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

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

Because light and exercise affect circadian rhythms separately through the SCN and peripheral clocks, respectively, researchers believe that combining these signals—exercise and morning sunlight—may work better to shift internal clocks to the time of both signals than either light or exercise alone.

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

And scientists know that powerful triggers at dawn help ensure a steady twilight. The circadian clocks, once triggered, start a precise countdown to the evening release of melatonin – the hormone that lulls us into a relaxed state ready for sleep.

Exercise and exposure to daylight can be synergistic in other ways: exercise causes the pupils in our eyes to dilate and capture more light, which can be especially helpful as the eyes lose sensitivity to light as people age.

Modern schedules and artificial light often disrupt people’s 24-hour biological cycles. Regular disruptions of these cycles, or circadian rhythms, are linked to chronic diseases and premature death.

The loss of a single hour when the clocks jump forward on March 8 may sound trivial, but the sudden mismatch between our internal clocks and the external ones can compromise sleep, well-being, road safety and heart health.

To manage these risks, experts suggest preparing for the transition a few days ahead by using the light-and-motion strategy. Wake up 15 to 20 minutes earlier each day from March 5 to 8 and go for a walk or jog outside one hour after waking (indoor light is usually not bright enough to reset internal clocks). These incremental changes will gradually acclimate your body to the clock change.

The more body parts you train, the better, explains Esser. She suggests trying to get a little out of breath by exercising at about 50 to 75 percent of full effort.

This preparation is especially important for elderly people or those with chronic diseases. Around age 40, people’s circadian rhythms begin to lose flexibility, resulting in “longer clock adjustments and a higher likelihood of a problem,” Esser says.

Certain habits can negate the benefits of the light-and-motion strategy. Food late at night or bright light later in the day can shift rhythms later, just as mornings lighten earlier, says Gad Asher, a biochemist at the Weizmann Institute of Science in Rehovot, Israel, who studies the body’s internal clocks.

After establishing an earlier, stronger circadian rhythm—and emerging unscathed—don’t throw out your new light-and-exercise habit, says Asher. Keep the rhythm steady to maintain health for a long time. “What really matters is your daily habits going forward,” he says.

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