Clock changes disrupt sleep, health, and well-being
Indira Gurubhagavatula of the Perelman School of Medicine explains how seasonal time changes affect the body’s internal clock, and offers tips for an easier transition.
3 min. read
Image: Rudzhan Nagiev via Getty Images
This weekend, many people across the country will engage in a twice-a-year ritual: changing their clocks by one hour. At this time of year, “falling back” marks the end of daylight saving time (DST), which was first formally adopted by the United States in 1918.
But what began as a wartime effort to save energy has since sparked more than a century of debate over its value. The U.S. has tried adopting it, repealing it, making it permanent, and shortening or lengthening it, all in search of the right balance between aligning daylight with active hours and maximizing safety, productivity, and energy savings.
The impact of seasonal time changes to health and well-being can range from fatigue and nausea to more serious outcomes. Penn Today spoke with Indira Gurubhagavatula, director of the Sleep Medicine Fellowship at the Perelman School of Medicine, to better understand how to cope with these disruptions to the sleep cycle.
The body does ‘tell time’
Everyone has a “master” internal clock controlled by an area of the brain called the suprachiasmatic nucleus (SCN), Gurubhagavatula says, that generates circadian rhythms—internal 24-hour cycles that regulate biological functions.
“Most people are aware of the sleep-wake rhythm, but this is just one of the rhythms,” she says, adding that circadian rhythms also regulate body temperature, digestion, hormone levels, and immune function.
But there are also “local clocks in various tissues in the body, our social clock, which dictates when we have to go to work or school, and the solar clock, which relates to the timing of sunrise and sunset,” Gurubhagavatula says. “We function best when all of these clocks are aligned.”
Penn researcher Indira Gurubhagavatula in the sleep lab.
(Courtesy of Indira Gurubhagavatula)
DST happens in spring and summer, while fall and winter follow standard, or “natural,” time. Under standard time, morning and evening light are more evenly balanced around noon, when the sun is highest overhead (solar noon).
By shifting the clock so that solar noon happens at 1 p.m., “we are not actually ‘saving daylight.’ We are just redistributing it by changing our social clocks so that more light happens in the night and less in the morning,” Gurubhagavatula says.
These shifts have implications.
“The time change is stressful on the cardiovascular system,” she says. “People may also feel a general sense of being unwell and may experience physical exhaustion, fatigue, headaches, nausea or queasiness, forgetfulness, or difficulty concentrating.”
Most people find “springing ahead” more challenging, Gurubhagavatula says. She explains that shifting light away from the morning to the evening makes it harder to fall asleep earlier and can lead to chronic sleep deprivation, with some people never fully adapting.
Certain populations struggle more
The SCN is under genetic control, Gurubhagavatula says, meaning that genes help set people’s circadian rhythms(e.g., night owls or morning larks). But the body also uses cues such as light to align internal clocks.
Both night owls and workers whose shifts start early in the morning tend to struggle during the DST period.
“Many high school students are night owls, and yet their schools often start the earliest,” Gurubhagavatula says. “During daylight saving time, they are at even greater risk for sleep deprivation,” adding that some schools are delaying start times to match adolescent circadian rhythms.
On the other hand, she says, “Older adults may have a harder time adjusting to standard time. They tend to have the opposite pattern of teens. More of them fall asleep in the early evening and are wide awake by 2 to 4 a.m.”
Small changes can help
For most people, strategies to ease the transition are usually more crucial when we “spring forward” versus when we “fall back.”
In the fall, Gurubhagavatula says, exposure to bright light, evening outdoor exercise, or a small amount of afternoon caffeine can help people stay awake longer in the days leading up to the switch to standard time.
In the spring, she recommends transitioning five to seven days ahead of the switch to DST by going to bed 10-15 minutes earlier; avoiding screens and lights an hour before bedtime; limiting caffeine, alcohol, marijuana, and cigarettes; and exercising to build up a “hunger” for sleep.
Time for a change
DST also poses a public health risk, says Gurubhagavatula, especially during the week after the time change in the spring. “Dark mornings can be dangerous,” she says, noting that when the U.S. tried permanent DST in 1973, there was an increase in the number of school children who died during that winter.
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