Twice a year, switching between daylight saving time and standard time throws us off our usual routine. We might expect to feel a bit sleepy or maybe even a little “off.” But springing forward or falling back an hour can have other surprising effects: It’s linked to changes in our health, diet and even tendency to get into an accident.
“Sleep is a kind of outward symbol of the timing processes of our body,” explained Chris Winter, M.D., author of “The Sleep Solution” and president of the Charlottesville Neurology and Sleep Medicine clinic in Virginia. “Our bodies function on an internal schedule, from hormone release to body temperature to cognition – and sleep is linked to them all.”
Blame this one on the hormones. “Appetite in general is often not the body requesting food; it’s the body anticipating food,” Dr. Winter explained. “When your body knows you eat lunch around 12:30 p.m. or so every day, it anticipates and prepares for the meal.”
Your body receives those signals from hormones, like ghrelin, which increases our cravings so we’re motivated to eat, and leptin, which affects feelings of satiety. “These two hormones are intimately associated with sleep, which is part of why when we’re not sleeping well, we tend to overeat,” Dr. Winter said. “It’s a tight hormonal balance and daylight-saving shifts can absolutely throw it off.”
Speaking of being thrown off, you may find daylight saving time shifts make you feel mentally fuzzy or slow. Sleep disruptions can conversely affect cognitive performance.
Back in 1999, Johns Hopkins and Stanford University researchers published a comprehensive study that analyzed 21 years’ worth of fatal car crash data. They found a small but notable increase in car crash deaths on the Monday after the switch to daylight saving time in the spring: 83.5 deaths, compared with 78.2 deaths on the average Monday.
And studies of workplace-specific accidents have uncovered similar links. Research published in 2009 showed the Monday after switching to daylight saving time saw a 5.7 percent jump in workplace injuries, and nearly 68 percent more workdays lost to injuries, meaning they were more severe. These conclusions were reached by analyzing U.S. Department of Labor and Mine Safety and Health Administration injury data from 1983 to 2006.
Here again, disruptions in our normal sleep schedule can throw off hormonal balances. Lack of proper sleep can exacerbate depressive feelings, anxiety, irritability, and mental exhaustion.
Studies show even partial sleep deprivation can have a negative effect on mood, and as Dr. Winter pointed out, this effect can snowball: When you feel stressed and anxious thanks to lack of sleep from the previous night, it’s hard to settle down for that night’s rest, too.
If you have teens in the house, take special note: “The effects of [daylight saving time] can have more impact on adolescents,” said André U. Aguillon, M.D., assistant professor at the University of Toledo’s medical school and program director of the university’s Sleep Medicine Fellowship Program. “Not only do they require more sleep than adults, but their habitual sleep-wake timing is typically delayed.”
The spring forward has links to heart attack and certain strokes
“The heart has a pretty significant circadian rhythm,” said Winter, who has studied brain-blood flow during sleep. “We tend to see that disrupted sleep may make people more vulnerable when we wake up – not causing a heart attack but perhaps exacerbating underlying conditions.”
A 2014 U.S. study showed one hour of sleep during the "spring forward" to daylight saving time raised the risk of having a heart attack the following Monday by 24 percent compared to other Mondays during the year. By contrast, when “falling back” later in the year to gain an extra hour of sleep, heart attack risk fell 21 percent on the following Tuesday after returning to standard time.
Similarly, a study presented at the American Academy of Neurology’s 2016 conference showed daylight saving time transitions may be linked to an increased risk of ischemic stroke.
Tips to adjust: Do's and don’ts
Do get as much light as possible when you wake up. Sure, you may not feel like throwing open those curtains as soon as you open your eyes. But this is “by far the most effective way to jumpstart the change,” Dr. Winter said. “Your body sets its rhythm in large part by light.”
Do exercise in the A.M. This gets you up and moving, as well as exposing you to light and raising your body temperature – all great ways to wake your body up.
Do go to bed at your typical time Saturday night before the clocks change. “As we are a typically sleep-deprived society, we should take advantage of the extra hour of sleep,” Dr. Aguillon said.
Don’t over-caffeinate. Enjoy your morning cup, or whatever your usual coffee habit may be. But don’t alter your caffeine routine by, for example, chugging a cup or two in the afternoon because you feel a slump.
Don’t take a nap. “This is where people fall off the wagon,” Dr. Winter said. “They’re tired so they nap in the middle of the day, but then when it’s time to go to bed that night or the next night they’re not ready, which can have a bad snowball effect.”
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