California now requires most high schools to start no earlier than 8:30 a.m. to support students’ well-being and safety.
June 28, 2022
Most American teenagers are sleep deprived: Fewer than one in four U.S. high school students gets the recommended eight hours of sleep per night.1
Researchers who study the relationship between sleep and depression are unanimous: Adequate sleep could greatly improve many U.S. teenagers’ mental health.
“Perpetually fatigued adolescents look and feel depressed,” says Rachel Widome of the University of Minnesota. Her research links adequate sleep to fewer symptoms of depression among teenagers.2
“Poor sleep and depression are reinforcing—depression interferes with sleep, and not enough sleep leaves someone feeling like they don’t have energy to engage in life, which is a symptom of depression.”
The notion that anyone “can push through on little sleep with little cost to mental health is a myth,” says Andrew Fuligni of the University California, Los Angeles. His research demonstrates that despite some individual variation, most teenagers need about 8.5 hours of sleep to function at their best.3
“Mental health is very sensitive to sleep,” he explains. “To operate at peak levels—emotionally and intellectually—most teens should sleep between eight and 10 hours each night. Less than seven and more than 11 hours is unhealthy.”
Telling teenagers to go to bed earlier is not the answer. The entire circadian-driven sleep cycle—both sleep and wake times—is temporarily pushed later in adolescence because of hormonal changes, Fuligni explains. Child health advocates have been calling for later school start times since the 1980s and 1990s, he notes.
Growing scientific evidence on the benefits of later school start times is behind a new California law, which goes into effect July 1, 2022, that will bar most high schools from starting classes before 8:30 a.m.
The key findings spurring school districts to consider later school start times come from Widome and colleagues, who tracked students at five public Minnesota high schools using wrist monitors (actigraphy) that accurately measured the students’ sleep.4 They showed that when schools instituted later start times, students slept longer and their need for catch-up sleep on the weekends shrank. Students’ bedtimes did not move with the later start time, and they continued to get better sleep over two years.
Additional evidence comes from analysis of a multi-year study conducted by Kayla Wahlstrom and colleagues at the University of Minnesota.5 They examined data on more than 9,000 students attending eight high schools in three states that switched to later start times and documented improved sleep. When schools started after 8:30 a.m., attendance, standardized test scores, and academic performance in math, English, science, and social studies increased, while tardiness declined. One school that shifted start times from 7:35 a.m. to 8:55 a.m. saw a 70% decline in the number of local car accidents among drivers ages 16 to 18.
Despite the documented benefits of later school start times, only about 15% of U.S. high schools start at 8:30 a.m. or later, while 42% start before 8:00 a.m., Widome reports. “Early high school start times are strictly a United States phenomenon,” she notes. “Europe and Australia do not start school so early.”
Some parents and school officials have voiced opposition to changing school start times because the current timing facilitates after-school sports and allows the same school buses to transport high schoolers early in the morning and young children afterward. Family schedules are also often built around early start times that enable “the older kids to get home first to watch the younger ones,” she says.
“It’s appalling that our nation is willing to accept that teens are extremely fatigued during their adolescent years,” says Widome, “when there is a straightforward evidence-based solution—starting school later.”
The mental health crisis among American youth began growing long before the coronavirus pandemic: In 2019, more than one in three high school students reported “persistent feelings of sadness or hopelessness,” representing a 40% increase from 2009, according to the U.S. Centers for Disease Control and Prevention (CDC).6
During that same period, teenagers’ nightly sleep dropped sharply: The share of high school students getting the recommended minimum of eight hours of sleep declined from nearly 31% in 2009 to around 22% in 2019.7
Research shows a strong connection between sleep and symptoms of depression. In a 2019 study, Widome and colleagues showed that about one in three students who slept less than six hours per night had a high number of depression symptoms compared with about one in 10 students who got adequate sleep.8 But inadequate sleep is one of many factors affecting teenagers’ mental health.
The rise in sleep-deprived teenagers is a long-term trend, reports Widome. “A lot in our society has changed in the last decade, including more time spent using screens—phones, games, computers—and marketing caffeine drinks to adolescents.” In her 2019 study, teenagers who had inadequate sleep tended to spend twice as much time on devices with screens than their peers and were more likely to use those devices after they went to bed.
“We know people feel better when they get enough sleep,” notes Widome. “If we improved sleep, how much of that is addressing the tiredness that looks like depression? It is easy to forget how critically important sleep is to our lives.”
One way that poor sleep appears to heighten the risk of depression is by activating the body’s stress response system. Fuligni and colleagues identified altered levels of cortisol—the stress hormone—in the saliva of teenagers with consistently inadequate sleep.9 In a related study, the researchers showed that inadequate sleep exacerbated the connection between daily stress and inflammation-triggering genes, another biological sign of stress.10
Poor sleep can keep the body’s stress response system on high alert long term, which can have a profound impact on many of the body’s systems—not just increasing the risk of depression but laying a foundation for chronic conditions such as heart disease later in life, according to Fuligni.
The researchers found that students in 10th and 11th graes who consistently reported inadequate sleep were more vulnerable to depression several years later.11 Interventions designed to improve sleep during the high-school years may prevent depression among young people in their early 20s, when an individual’s risk of depression is highest, the researchers suggest.
Starting high schools later in the morning is the number one way to improve teenagers’ sleep, both Fuligni and Widome say. They express concerns over legislation to make Daylight Saving Time permanent because more high school students would go to school in the dark and wouldn’t see the sun rise until after their first period classes.
Widome favors permanent Standard Time, which would set sunrise earlier—helpful to teenagers’ waking—despite earlier evening sunsets. Both Fuligni and Widome agree that the current switch from Daylight Saving Time that moves clocks ahead in spring is a challenging adjustment for teenagers.
Along with later school start times, Fuligni would like to see school administrators and teachers assess whether students are sacrificing sleep for homework and adjust their expectations. If Widome were making school policy, she also would eliminate online assignments that have midnight due dates and ban high school clubs from meeting before 8:00 a.m.
“We need to really value sleep,” she says, “not see it as something extraneous that is only for the weak.”
This article was produced under a grant from the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD). The work of researchers from the following NICHD-funded Population Dynamics Research Centers was highlighted: University of Minnesota (5P2CHD041023-19) and University of California, Los Angeles (5P2CHD041022-19).
 Centers for Disease Control and Prevention (CDC), High School Students Who Got 8 or More Hours of Sleep, YRBS Explorer.
 Aaron T. Berger, Kyla L. Wahlstrom, Rachel Widome, “Relationships Between Sleep Duration and Adolescent Depression: A Conceptual Replication,” Sleep Health 5, no. 2 (2019): 175-9, doi:10.1016/j.sleh.2018.12.003.
 Andrew J. Fuligni et al., “Individual Differences in Optimum Sleep for Daily Mood During Adolescence,” Journal of Clinical Child and Adolescent Psychology 48, no. 3 (2019): 469-79.
 Rachel Widome et al., “Association of Delaying School Start Time With Sleep Duration, Timing, and Quality Among Adolescents,” JAMA Pediatrics 174, no. 7 (2020): 697-704, doi:10.1001/jamapediatrics.2020.0344.
 Kayla L. Wahlstrom et al, Examining the Impact of Later School Start Times on the Health and Academic Performance of High School Students: A Multi-Site Study (Center for Applied Research and Educational Improvement, University of Minnesota, St. Paul, MN: 2014).
 CDC, “Adolescent and School Health: Mental Health,” n.d.
 CDC, High School Students Who Got 8 or More Hours of Sleep.
 Rachel Widome et al., “Correlates of Short Sleep Duration Among Adolescents,” Journal of Adolescence 77 (2019): 163-7.
 Kate Ryan Kuhlman et al., “Sleep Problems in Adolescence Are Prospectively Linked to Later Depressive Symptoms Via the Cortisol Awakening Response,” Developmental Psychopathology 32, no. 3 (2020): 997-1006.
 Jessica J. Chiang et al., “Daily Interpersonal Stress, Sleep Duration, and Gene Regulation During Late Adolescence,” Psychoneuroendocrinology 103 (2019): 147-55, doi: 10.1016/j.psyneuen.2018.11.026.
 Kate Ryan Kuhlman et al., “Persistent Low Positive Affect and Sleep Disturbance Across Adolescence Moderate Link Between Stress and Depressive Symptoms in Early Adulthood,” Journal of Abnormal Child Psychology 48, no. 1 (2020): 109-21, doi: 10.1007/s10802-019-00581-y.