Around the world, children get an hour less sleep than they did thirty years ago. The cost: IQ points, emotional well-being, ADHD, and obesity.
Morgan Fichter is a ten-year-old fifth-grader in Roxbury, New Jersey. She’s fair-skinned and petite, with freckles across her nose and wavy, light brown hair. Her father, Bill, is a police sergeant on duty until three a.m. Her mother, Heather, works part-time, devoting herself to shuffling Morgan and her brother to their many activities. Morgan plays soccer (Heather’s the team coach), but Morgan’s first love is competitive swimming, with year-round workouts that have broadened her shoulders. She’s also a violinist in the school orchestra, with two practices and a private lesson each week, on top of the five nights she practices alone. Every night, Heather and Morgan sit down to her homework, then watch Flip This House or another design show on TLC. Morgan has always appeared to be an enthusiastic, well-balanced child.
But once Morgan spent a year in the classroom of a hypercritical teacher, she could no longer unwind at night. Despite a reasonable bedtime of 9:30 p.m., she would lay awake in frustration until 11:30, sometimes midnight, clutching her leopard-fur pillow. On her fairy-dust purple bedroom walls were taped index cards, each a vocabulary word Morgan had trouble with. Unable to sleep, she turned back to her studies, determined not to let her grades suffer. Instead, she saw herself fall apart emotionally. During the day, she was crabby and prone to crying easily. Occasionally Morgan fell asleep in class.
Morgan moved on from that teacher’s classroom the next year, but the lack of sleep persisted. Heather began to worry why her daughter couldn’t sleep. Was it stress, or hormones? Heather forbade caffeinated soda, especially after noon, having noticed that one cola in the afternoon could keep her daughter awake until two a.m. Morgan held herself together as best she could, but twice a month she suffered an emotional meltdown, a kind of overreacting crying tantrum usually seen only in three-year-olds who missed their nap. “I feel very sad for her,” Heather agonized. “I wouldn’t wish it on anyone—I was worried it was going to be a problem forever.”
Concerned about her daughter’s well-being, Heather asked the pediatrician about her daughter’s sleep. “He kind of blew me off, and didn’t seem interested in it,” she recalled. “He said, ‘So, she gets tired once in a while. She’ll outgrow it.’ ”
The opinion of Heather’s pediatrician is typical. According to surveys by the National Sleep Foundation, 90% of American parents think their child is getting enough sleep.
The kids themselves say otherwise: 60% of high schoolers report extreme daytime sleepiness. A quarter admit their grades have dropped because of it. Depending on what study you look at, anywhere from 20% to 33% are falling asleep in class at least once a week.
The raw numbers more than back them up. Half of all adolescents get less than seven hours of sleep on weeknights. By the time they are seniors in high school, according to studies by Dr. Frederick Danner at the University of Kentucky, they’re averaging only slightly more than 6.5 hours of sleep a night. Only 5% of high school seniors average eight hours. Sure, we remember being tired when we went to school. But not like today’s kids.
It is an overlooked fact that children—from elementary school through high school—get an hour less sleep each night than they did thirty years ago. While modern parents obsess about our babies’ sleep, this concern falls off the priority list after preschool. Even kindergartners get thirty minutes less a night than they used to.
There are as many causes for this lost hour of sleep as there are types of family. Overscheduling of activities, burdensome homework, lax bedtimes, televisions and cell phones in the bedroom—they all contribute. So does guilt; home from work after dark, parents want time with their children and are reluctant to play the hardass who orders them to bed. (One study from Rhode Island found that 94% of high schoolers set their own bedtimes.) All these reasons converge on one simple twist of convenient ignorance—until now, we could ignore the lost hour because we never really knew its true cost to children.
Using newly developed technological and statistical tools, sleep scientists have recently been able to isolate and measure the impact of this single lost hour. Because children’s brains are a work in progress until the age of 21, and because much of that work is done while a child is asleep, this lost hour appears to have an exponential impact on children that it simply doesn’t have on adults.
The surprise is not merely that sleep matters—but how much it matters, demonstrably, not just to academic performance and emotional stability, but to phenomena that we assumed to be entirely unrelated, such as the international obesity epidemic and the rise of ADHD. A few scientists theorize that sleep problems during formative years can cause permanent changes in a child’s brain structure—damage that one can’t sleep off like a hangover. It’s even possible that many of the hallmark characteristics of being a tweener and teen—moodiness, depression, and even binge eating—are actually just symptoms of chronic sleep deprivation.
Dr. Avi Sadeh at Tel Aviv University is one of the dozen or so bigwigs in the field, frequently collaborating on papers with the sleep scholars at Brown University. A couple years ago, Sadeh sent 77 fourth-graders and sixth-graders home with randomly-drawn instructions to either go to bed earlier or stay up later, for three nights. Each child was given an actigraph—a wristwatch-like device that’s equivalent to a seismograph for sleep activity—which allows the researchers to see how much sleep a child is really getting when she’s in bed. Using the actigraphy, Sadeh’s team learned that the first group managed to get 30 minutes more of true sleep per night. The latter got 31 minutes less of true sleep.
After the third night’s sleep, a researcher went to the school in the morning to give the children a test of neurobiological functioning. The test, a computerized version of parts of the Wechsler Intelligence Scale for Children, is highly predictive of current achievement test scores and how teachers rate a child’s ability to maintain attention in class.
Sadeh knew that his experiment was a big risk. “The last situation I wanted to be in was reporting to my grantors, ‘Well, I deprived the subjects of only an hour, and there was no measurable effect at all, sorry—but can I have some more money for my other experiments?’ ”
Sadeh needn’t have worried. The effect was indeed measurable—and sizeable. The performance gap caused by an hour’s difference in sleep was bigger than the gap between a normal fourth-grader and a normal sixth-grader. Which is another way of saying that a slightly-sleepy sixth-grader will perform in class like a mere fourth-grader. “A loss of one hour of sleep is equivalent to [the loss of] two years of cognitive maturation and development,” Sadeh explained.
“Sadeh’s work is an outstanding contribution,” says Penn State’s Dr. Douglas Teti, Professor of Human Development and Family Studies. His opinion is echoed by Brown’s Dr. Mary Carskadon, a specialist on the biological systems that regulate sleep. “Sadeh’s research is an important reminder of how fragile children are.”
Sadeh’s findings are consistent with a number of other researchers’ work—all of which points to the large academic consequences of small sleep differences. Dr. Monique LeBourgeois, also at Brown, studies how sleep affects prekindergartners. Virtually all young children are allowed to stay up later on weekends. They don’t get less sleep, and they’re not sleep deprived—they merely shift their sleep to later at night on Fridays and Saturdays. Yet she’s discovered that the sleep shift factor alone is correlated with performance on a standardized IQ test. Every hour of weekend shift costs a child seven points on the test. Dr. Paul Suratt at the University of Virginia studied the impact of sleep problems on vocabulary test scores taken by elementary school students. He also found a seven-point reduction in scores. Seven points, Suratt notes, is significant: “Sleep disorders can impair children’s IQ as much as lead exposure.”
If these findings are accurate, then it should add up over the long term: we should expect to see a correlation between sleep and school grades. Every study done shows this connection—from a study of second- and third-graders in Chappaqua, New York, up to a study of eighth-graders in Chicago.
These correlations really spike in high school, because that’s when there’s a steep drop-off in kids’ sleep. University of Minnesota’s Dr. Kyla Wahlstrom surveyed over 7,000 high schoolers in Minnesota about their sleep habits and grades. Teens who received A’s averaged about fifteen more minutes sleep than the B students, who in turn averaged fifteen more minutes than the C’s, and so on. Wahlstrom’s data was an almost perfect replication of results from an earlier study of over 3,000 Rhode Island high schoolers by Brown’s Carskadon. Certainly, these are averages, but the consistency of the two studies stands out. Every fifteen minutes counts.