The return to "standard time" is better for our health according to sleep scientists, but the time change can be disruptive, and our bodies must also adjust to more hours of darkness as we head towards winter.
The body is an exquisite time-keeping machine. And growing evidence shows that if you align your daily habits with your circadian rhythms — including when you sleep, eat, and exercise — you can help fend off chronic disease and optimize good health.
Let's start with a quick primer: "Your body is filled with clocks," explains Emily Manoogian, a researcher and chronobiologist at the Salk Institute for Biological Studies. In addition to the master clock in your brain, there are time-keeping mechanisms in every organ and in your cells.
"Every cell in your body that has DNA has a molecular clock that keeps its own time," she says. They're all part of your body's circadian system helping you stay in sync with the 24-hour cycle.
But our bodies don't keep perfect time on their own. Every day, we stray a bit from the 24-hour cycle, and need a reset, explains Salk Institute researcher Satchin Panda, author of The Circadian Code: Lose Weight, Supercharge Your Energy, and Transform Your Health from Morning to Midnight.
"The master clock in your brain coordinates all the other clocks through a series of different cues," Manoogian explains, including external cues — such as light, food, and movement. And that's why the timing of our habits can play a pivotal role in keeping our clocks in sync.
Light from the sun serves as the external cue to resynchronize the master clock. That's why it's helpful to open the blinds in the morning and spend time outdoors.
And, it turns out, our first bite of food each day also works as an external cue to sync the clocks in our digestive system and throughout our bodies.
"Food is also a signal to reset the clocks, especially your gut," Manoogian says. "That's one of the reasons why making sure you're eating at the right time relative to light is important."
Eating is a cue to wake up your digestive and metabolic organs, which are primed to function best during the day. By nighttime, the metabolic system is ready for rest, too.
"When you're asleep, your body expects to fast. And so it shuts down the part of the system that captures glucose from the blood and stores it away," she explains.
When people eat too close to bedtime or in the middle of the night, their metabolic organs aren't optimized to do their job. The misalignment can lead to poor blood sugar control. Her research shows that restricting the number of hours you eat during a day to about a 10 hour window, can lead to significant improvements in metabolic health.
There's lots of evidence that eating out of sync with your circadian rhythms can increase the risk of metabolic diseases, including diabetes and obesity. Studies show that shift workers who work rotating, overnight shifts have a higher risk of developing these conditions due, in part, to the disruption of the natural rhythms.
And when it comes to exercise, some people find they do best in the morning, others in the afternoon, says Dr. Phyliss Zee, director of the Center for Sleep and Circadian Medicine at Northwestern University Feinberg School of Medicine. But the science shows exercising late at night, just before bed can disrupt sleep.
"There's a peak time for almost every physiological process," Zee says. "The timing of feeding, the time that you exercise, the physical activity, all of these help entrain the clocks in your body so that they're in sync," she says.
If you eat dinner and go to bed around the same time most nights, your 'creature of habit' ways could pay off. "The science shows that regularity is very important for the circadian system and for health," Zee says.
And while each person is unique she says, a general rule of thumb is to begin limiting exposure to light, food and heavy exercise starting a few hours before bedtime.
But as scientists have learned more about the importance of keeping our biological clocks in sync, society has moved in the opposite direction. Manoogian points to advertisements for midnight food menus, and around the clock work and entertainment as examples of our 24/7 modern life.
One way to push back is to track your daily habits. Michelle Pittsley, who lives in Vista, Calif., started using an app called myCircadianClock to log her eating and blood sugar. She says it helped her stick to a "time-restricted eating" window and helped her track her progress. The app was developed by Salk scientists as a research tool, and is used in Salk Institute studies. It's free to any adult who downloads it. The app provides guidance on when to sleep, eat, and exercise. (Note: if you sign up, you're sharing data with researchers.)
When we have "broken" circadian rhythms, the risk for chronic disease rises, including obesity, diabetes, heart disease, fatty liver disease, gut diseases and common cancers, say Panda and Manoogian. If you want to be more intentional about aligning your habits for better health, here are three strategies to try.
1. Drop the late night snack, and limit the hours you eat.
People who restrict their eating to a ten hour window can reduce their risk of Type 2 diabetes, Manoogian says. She and Panda co-authored a study of 108 adults, average age 59, who had symptoms of metabolic disease. They found those who followed time-restricted eating saw a significant reduction in their hemoglobin A1c (which is a person's average glucose level over a few months), compared to participants who did not restrict their eating window.
Participants were not asked to reduce calories, only to restrict the eating window for a period of three months.
"It was exciting to see that just the time restricted eating was able to reduce their risk for Type 2 diabetes by 60%," Manoogian says, because the reduction in blood sugar, if maintained, reduces the risk of the disease.
Research also suggests that eating your biggest meal of the day in the afternoon, as opposed to later in the evening can be beneficial for those who want to lose weight. A study from Spain found early eaters lost 25 percent more weight than late eaters. Panda says when his mother gave up a late night snack that included tea with sugar and milk and an occasional snack, that one change led to a significant drop in her blood sugar levels.
2. Go to bed about the same time most nights
"Keeping the same sleep schedule is optimal," Manoogian says. The consistency gives your body a chance to anticipate and keep internal clocks synchronized. During sleep, waste is cleared out of our brains, and memories are consolidated, and there's a pile of evidence to show rest is critical for our health.
But don't beat yourself up when you have a late night out. And of course, there will be disruptions due to travel, work deadlines or weekend celebrations. "Going off your circadian system is not like breaking an arm," Manoogian says. Think of the harms of erratic schedules akin to the way dripping water can erode stone. "Little hits, time after time, can wear down the system," she says. And the result is you can feel slower and older.
There are lots of bedtime rituals to foster a good night's sleep, including limiting light before bed and sleeping in darkness. Zee's research shows even small amounts of light while sleeping can have adverse effects on cardiovascular and metabolic health.
3. Time exercise to your 'sweet spot,' but not too late at night
Whether you're a morning lark or a night owl can influence the ideal time for you to exercise, so this will vary from person to person, Zee says. "The better time to exercise depends, in part, on what we call your chronotype," she says, which is a person's innate preference for timing of sleep or when they feel more alert and energetic. One way to estimate your tendency is with a Morningness-Eveningness questionnaire.
"If you're a morning person, then morning exercise can be beneficial," creating a consistent structure, Zee says, but people who grow more alert later in the day, may want to put it off until later. As people juggle competing obligations, exercise may be shoehorned into the time it fits on your calendar, even if it's not your body clock's preferred window. She says it's important to remember that exercise is beneficial, no matter what time you do it.
But keep this in mind: "Exercise is a stimulatory cue to tell your body you should be awake," Manoogian says, so it's not a surprise that recent research shows that exercise just before sleep can disrupt sleep quality .
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