It is a widely held belief that sleep quality can be improved by avoiding exercise in the evening. However, as researchers from the Institute of Human Movement Sciences and Sport at ETH Zurich have demonstrated, it is not generally true. The scientists combed through the literature on the subject and analyzed all 23 studies that met their quality requirements. They concluded that doing exercise in the four hours before going to bed does not have a negative effect on sleep. "If doing sport in the evening has any effect on sleep quality at all, it's rather a positive effect, albeit only a mild one," says Christina Spengler, head of the Exercise Physiology Lab at ETH Zurich.
The researchers showed that in the night after study participants had done some sport in the evening, they spent 21.2 percent of their sleeping time in deep sleep. Following an evening without exercise, the average figure was 19.9 percent. While the difference is small, it is statistically significant. Deep sleep phases are especially important for physical recovery. Vigorous training within an hour before bedtime is an exception to the rule.
It is the only type of evening exercise that may have a negative effect on sleep, according to this analysis. "However, this preliminary observation is based on just one study," Spengler says. "As a rule of thumb, vigorous training is defined as training in which a person is unable to talk. Moderate training is physical activity of an intensity high enough that a person would no longer be able to sing, but they could speak." One example of vigorous training is the kind of high-intensity interval training that competitive athletes often perform. In many cases, though, a longer endurance run or a longer ride on a racing bike would fall into the moderate training category.
As the analysis showed, it took study participants who completed an intensive training session shortly before bedtime longer to fall asleep. The study also provided insight into why this is the case: the test subjects were not able to recover sufficiently in the hour before they went to bed. Their hearts were still beating more than 20 beats per minute faster than their resting heart rate.
Improving Sleep Quality
People should do at least 150 minutes of moderate exercise each week, according to the official recommendations of sport physicians. Many may ask themselves: Should I exercise in the evening if I didn't have time during the day or will that have a negative effect on my sleep? "People can do exercise in the evening without hesitation,” says Jan Stutz, a doctoral student in Spengler's research group and lead author of the analysis, which was published in the journal Sports Medicine. “The data shows that moderate exercise in the evening is no problem at all. Moderate exercise did not cause sleep problems in any of the studies examined, not even when the training session ended just 30 minutes before bedtime. However, vigorous training or competitions should be scheduled earlier in the day, if possible."
Stutz and Spengler point out that they examined average values over the course of their analysis, which made only general statements possible. "Not everyone reacts to exercise in the same way, and people should keep listening to their bodies,” Stutz says. “If they notice they are having problems falling asleep after doing a sport, they should try to work out a little earlier." "It is well known that doing exercise during the day improves sleep quality," Spengler added. "Now we have shown that, at the very least, exercising in the evening doesn't have a negative effect."
Teens Get More Sleep With Later School Start Time
When Seattle Public Schools announced that it would reorganize school start times across the district for the fall of 2016, the massive undertaking took more than a year to deploy. Elementary schools started earlier, while most middle and all of the district's 18 high schools shifted their opening bell almost an hour later - from 7:50 a.m. to 8:45 a.m. Parents had mixed reactions. Extracurricular activity schedules changed. School buses were redeployed. And as hoped, teenagers used the extra time to sleep in.
In a paper published in the journal Science Advances, researchers at the University of Washington and the Salk Institute for Biological Studies announced that teens at two Seattle high schools got more sleep on school nights after start times were pushed later - a median increase of 34 minutes of sleep each night. This boosted the total amount of sleep on school nights for students from a median of six hours and 50 minutes, under the earlier start time, to seven hours and 24 minutes under the later start time. "This study shows a significant improvement in the sleep duration of students - all by delaying school start times so that they're more in line with the natural wake-up times of adolescents," says senior and corresponding author Horacio de la Iglesia, a UW professor of biology.
The study collected light and activity data from subjects using wrist activity monitors rather than relying solely on self-reported sleep patterns from subjects, as is often done in sleep studies to show that a later school start time benefits adolescents by letting them sleep longer each night. The study also revealed that, after the change in school start time, students did not stay up significantly later: They simply slept in longer, a behavior that scientists say is consistent with the natural biological rhythms of adolescents. "Research to date has shown that the circadian rhythms of adolescents are simply fundamentally different from those of adults and children," says lead author Gideon Dunster, a UW doctoral student in biology.
In humans, the churnings of our circadian rhythms help our minds and bodies maintain an internal "clock" that tells us when it is time to eat, sleep, rest and work on a world that spins once on its axis approximately every 24 hours. Our genes and external cues from the environment, such as sunlight, combine to create and maintain this steady hum of activity. But the onset of puberty lengthens the circadian cycle in adolescents and also decreases the rhythm's sensitivity to light in the morning. These changes cause teens to fall asleep later each night and wake up later each morning relative to most children and adults. "To ask a teen to be up and alert at 7:30 a.m. is like asking an adult to be active and alert at 5:30 a.m.," says de la Iglesia.
Scientists generally recommend that teenagers get eight to 10 hours of sleep each night. But early-morning social obligations such as school start times force adolescents to either shift their entire sleep schedule earlier on school nights or truncate it. Certain light-emitting devices such as smartphones, computers and even lamps with blue-light LED bulbs can interfere with circadian rhythms in teens and adults alike, delaying the onset of sleep, de la Iglesia added.
Only one-quarter of high school age adolescents reported sleeping the minimum recommended eight hours each night, according to a survey of youth released in 2017 by the U.S. Centers for Disease Control and Prevention. "All of the studies of adolescent sleep patterns in the United States are showing that the time at which teens generally fall asleep is biologically determined but the time at which they wake up is socially determined," says Dunster. "This has severe consequences for health and well-being, because disrupted circadian rhythms can adversely affect digestion, heart rate, body temperature, immune system function, attention span and mental health."
The UW study compared the sleep behaviors of two separate groups of sophomores, all enrolled in biology classes at Roosevelt and Franklin high schools. One group of 92 students, drawn from both schools, wore wrist activity monitors all day for two-week periods in the spring of 2016, when school still started at 7:50 a.m. The wrist monitors collected information about light and activity levels every 15 seconds, but no physiological data about the students. In 2017, about seven months after school start times had shifted later, the researchers had a second group of 88 students - again drawn from both schools - wear the wrist activity monitors.
Researchers used both the light and motion data in the wrist monitors to determine when the students were awake and asleep. Two teachers at Roosevelt and one at Franklin worked with the UW researchers to carry out the study, which was incorporated into the curriculum of the biology classes. Students in both groups also self-reported their sleep data. The information obtained from the wrist monitors revealed the significant increase in sleep duration, due largely to the effect of sleeping in more on weekdays. "Thirty-four minutes of extra sleep each night is a huge impact to see from a single intervention," said de la Iglesia.
The study also revealed other changes beyond additional shut-eye. After the change, the wake-up times for students on weekdays and weekends moved closer together. And their academic performance, at least in the biology course, improved: Final grades were 4.5 percent higher for students who took the class after school start times were pushed back compared with students who took the class when school started earlier. In addition, the number of tardies and first-period absences at Franklin dropped to levels similar to those of Roosevelt students, which showed no difference between pre and post-change.
The researchers hope that their study will help inform ongoing discussions in education circles about school start times. The American Academy of Pediatrics recommended in 2014 that middle and high schools begin instruction no earlier than 8:30 a.m., though most U.S. high schools start the day before then. In 2018, California lawmakers nearly enacted a measure that would ban most high schools from starting class before 8:30 a.m. In 2019, Virginia Beach, home to one of the largest school districts in Virginia, will consider changes to its school start times.
More than a third of Americans don’t get enough sleep, and growing evidence suggests it’s not only taking a toll on their physical health through heart disease, diabetes, stroke, or other conditions, but hurting their mental health as well. Those who are sleep deprived lose some of their ability to be positive-minded people, according to a recent study led by Postdoctoral Fellow Ivan Vargas, Ph.D., in the journal Cognitive Therapy and Research. That may not sound serious, but medical experts say an inability to think positively is a serious symptom of depression that could be dangerous if left unaddressed. An estimated 16.1 million adults experienced a major depressive episode in 2014. “In general, we have a tendency to notice positive stimuli in our environment,” says Vargas. “We tend to focus on positive things more than anything else, but now we’re seeing that sleep deprivation may reverse that bias.”
The study team took 40 healthy adults and randomized them to either 28 consecutive hours awake or a full eight hours of sleep. All participants participated in a computer test measuring their accuracy and response time at identifying happy, sad and neutral faces to assess how they pay attention to positive or negative information. The team found that those who were acutely sleep deprived were less likely to focus on the happy faces. They didn’t necessarily focus more on the negative, but were less likely to focus on the positive. The study may have implications for those experiencing depression and/or anxiety.
There are many symptoms of depression including feeling sad and no longer being able to enjoy things you typically would, but poor sleep is associated with a particularly serious sign of the condition. “Depression is typically characterized as the tendency to think and feel more negatively or sad, but more than that, depression is associated with feeling less positive, less able to feel happy,” Vargas says. “Similarly, if you don’t get enough sleep, it reduces your ability to attend to positive things, which over time may confer risk for depression.”
In the present study, those with a history of insomnia symptoms were less sensitive to the effects of the sleep loss. The authors believe this might be because those with a history of insomnia symptoms have more experience being in sleep-deprived conditions and have developed coping methods to modulate the effect of sleep loss. Vargas and colleagues recently presented a related study on the association of insomnia and suicide, finding that people who suffer from insomnia are three times more likely to report thoughts of suicide and death during the past 30 days than those without the condition.
The study comes amid a growing body of knowledge associating sleep disorders and depression. For example, ongoing research presented at SLEEP 2017 from a multi-center NIH-sponsored Treatment of Insomnia and Depression study suggests that cognitive-behavioral therapy for insomnia (CBT-I) may help achieve depression remission in those suffering from both depression and insomnia who sleep at least seven hours each night. Additionally, a study in the journal Child Development furthers our understanding of the connection between late night cell phone use, mental health, and disrupted sleep, finding that using a cell phone at night can increase depression in teenagers and lower their self-esteem.
Understanding Sleep-Wake Rhythms
The sleep rhythms that reflect circadian systems peak later in teenagers than in adults, and vary as much as 10 hours in individuals across at any ages, according to a study published in the journal PLOS ONE by Dorothee Fischer from Harvard T.H. Chan School of Public Health, and colleagues. People's circadian systems synchronize with light and darkness in the environment, giving rise to chronotypes: individual rhythms in physiology, cognition and behavior. For example, people with early chronotypes have earlier sleep times, while those with late chronotypes have later sleep times and can sleep into the day. Currently, 30 percent of the U.S. workforce has unusual work schedules, such as alternating or extended shifts and on-call duty. These unusual schedules are linked with health and safety risks. Chronotype-tailored schedules might help minimize those risks.
To investigate chronotypes variation in the U.S., Fischer and colleagues analyzed self-reported data from 53,689 respondents of the American Time Use Survey from 2003 to 2014. The researchers used the mid-point of sleep on weekends as a proxy for chronotype. The researchers found that sleep chronotypes vary widely, both over an individual's lifetime amongst age groups as well as amongst individuals. The greatest difference in chronotypes is during adolescence and early adulthood. Chronotypes become later during adolescence, peaking in lateness at about age 19. The average chronotype, or mid-point of sleep, at age 17 to 18 was 4:30 a.m., compared to 3:00 a.m. at age 60. Most U.S. public schools start at 8:30 a.m. or earlier, suggesting that high school students go to school during their biological night. This work supports delaying school start times to benefit the sleep and circadian alignment of high school students.
In addition, the researchers found that chronotypes vary up to 10 hours from individual to individual regardless of age. This may provide opportunities for tailoring work schedules to chronotypes, which is important because syncing workers with their optimal work times could help minimize health and safety risks. "The timing for optimal sleep can be as different as 10 hours among individuals, meaning that opposite chronotypes could share a bed without knowing that they do. What chronotype you are, is influenced by age and gender: on average, older people are earlier chronotypes than younger people and women are earlier chronotypes than men during the first half of their lives."
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