Getting more exercise or spending more time sedentary—even for just one day—can change a teenager’s sleep, a new study shows.
In a one-week, micro-longitudinal study, researchers found that when teens got more physical activity than they usually did, they fell asleep earlier, slept longer, and slept better that night.
Specifically, for every extra hour of moderate-to-vigorous physical activity, the teens fell asleep 18 minutes earlier, slept 10 minutes longer, and had about one percent greater sleep maintenance efficiency that night.
“Adolescence is a critical period to obtain adequate sleep, as sleep can affect cognitive and classroom performance, stress, and eating behaviors,” says Lindsay Master, a data scientist at Penn State. “Our research suggests that encouraging adolescents to spend more time exercising during the day may help their sleep health later that night.”
In contrast, researchers also found that being sedentary more during the day was associated with worse sleep health. When participants were sedentary for more minutes during the day, they fell asleep and woke up later but slept for a shorter amount of time overall.
The findings, which appear in Scientific Reports, help illuminate the complex relationship between physical activity and sleep, says Orfeu Buxton, professor of biobehavioral health.
“You can think of these relationships between physical activity and sleep almost like a teeter totter,” Buxton says. “When you’re getting more steps, essentially, your sleep begins earlier, expands in duration, and is more efficient. Whereas if you’re spending more time sedentary, it’s like sitting on your sleep health: Sleep length and quality goes down.”
Tossing and turning
While previous research suggests that adolescents need 8 to 10 hours of sleep a night, recent estimates suggest that as many as 73 percent of adolescents are getting less than eight.
Previous research also shows that people who are generally more physically active tend to sleep longer and have better sleep quality. But less is known about whether day-to-day changes in physical activity and sedentary behavior affected sleep length and quality, researcher say.
For the new study, researchers used data from 417 participants in the Fragile Families and Child Well-being study, a national cohort from 20 United States cities. When they were 15, participants wore accelerometers on their wrists and hips to measure sleep and physical activity for one week.
“One of the strengths of this study was using the devices to get precise measurements about sleep and activity instead of asking participants about their own behavior, which can sometimes be skewed,” Master says.
“The hip device measured activity during the day, and the wrist device measured what time the participants fell asleep and woke up, and also how efficiently they slept, which means how often they were sleeping versus tossing and turning.”
In addition to finding links between how physical activity affects sleep later that night, the researchers also found connections between sleep and activity the following day. When participants slept longer and woke up later, they engaged in less moderate-to-vigorous physical activity and sedentary behavior the next day.
“This finding might be related to a lack of time and opportunity the following day,” Master says. “We can’t know for sure, but it’s possible that if you’re sleeping later into the day, you won’t have as much time to spend exercising or even being sedentary.”
Becoming your best self
Improving health is something that can, and should, take place over time, Buxton says.
“Becoming our best selves means being more like our best selves more often. We were able to show that the beneficial effects of exercise and sleep go together, and that health risk behaviors like sedentary time affect sleep that same night. So if we can encourage people to engage in more physical activity and better sleep health behaviors on a more regular basis, it could improve their health over time.”
The researchers will continue to follow up with the participants to see how health and health risk behaviors continue to interact, and how sleep health influences thriving in early adulthood.
Additional researchers are from Penn State, Stony Brook University, the University of South Florida, and Harvard Medical School. The Eunice Kennedy Shriver National Institute of Child Health and Human Development of the National Institutes of Health and several private foundations funded the work.
Source: Penn State