wpe17.jpg (6911 bytes)
March 1999

Sorry I'm Late...
It's My Circadian Rhythms

AG00041_.gif (503 bytes) Back to the College's Home Page

By Marina Quattrocchi

Ever wonder why 12 students are late to your first period class every Monday? Why those who do make it on time are continually dozing off? Why detentions, phone calls home and losing marks do not seem to have any effect? Why this never seems to be a problem in elementary school?

Chances are, if you've had time to look into it, you’ll find that Sally, who has been late 20 times in two months, never had a problem before she hit high school. She's not chronically late for her other classes, and she is never late for her job at Pizza Hut; in fact she's a model employee. She’s only there on time because she's being paid, you say. Not so.

Research shows that the thousands of high school students who drag themselves in like reluctant canines to a soapy bath may have good reason to growl in the morning. It all has to do with their circadian rhythms, that internal clock that governs sleep patterns. If you’ve ever had jet lag, you know exactly how it feels to upset your circadian rhythm. Unfortunately for Sally in your period one class, she may be in a continual state of jet lag if she goes to bed at 11:30 after doing her homework, then tries to get up 6:30 a.m. for school.


The first researcher to delve into circadian rhythms was French scientist Jean Jacques d’Ortous de Mairan. He wondered why plants opened their leaves during the day, then closed them at night. He hypothesized that plants respond to the external cues of the sunlight. To his amazement, he found that when the plants are kept in a completely dark room their leaves open and close on the same schedule. Like humans, plant rhythms are governed by an internal clock.

Only in the last two decades have researchers fully understood the dynamics of circadian rhythms. Circadian comes from the Latin word circa meaning about and dian meaning a day. For most adults and children, this natural rhythm is close to a 24-hour cycle. But for teenagers this rhythm slows. Typical teenagers do not want to go to bed at 11 p.m. because their internal clock is telling them it’s only 8 p.m.

This is why it is like pulling teeth to get a teenager out of bed in the morning. When their alarm clock rings at 7 a.m., their body is telling them it’s 4 a.m. For roughly 10 years, teenagers groggily deal with an internal clock that runs much slower, on a cycle of 26 to 30 hours. "It is not that the younger generation is bad, lazy or shiftless, their clocks simply are running on a slower time," say researchers Shirley Linde and Peter Hauri. Hauri is director of the Mayo Clinic Insomnia Program.

As adolescents mature their internal clocks undergo a shift, pushing their pre-programmed period of wakefulness about an hour later than most children and adults. This shift is due to a delay in the timing of a nightly squirt of melatonin from the pineal gland, inside the brain. Melatonin, which induces sleepiness, helps set the body’s circadian rhythms. This squirt of melatonin occurs at roughly 9:30 p.m. for younger adolescents, then changes to 10:30 for teenagers.

This means that starting times in many schools are backwards. Elementary schools could begin much earlier, since children at this age are more alert and ready to learn early in the morning. A perfect scenario for many teens would be a school day beginning at 10 a.m.


Much of what we know about teenagers and sleep grew from research in the United States in the 1980s by Mary Carskadon, who now directs the E.P Bradley Hospital sleep research laboratory in Providence, Rhode Island, and Ronald E. Dahl, director of the child and adolescent sleep laboratory at the University of Pittsburgh Medical Center.

Teenagers have a physiological need for extra sleep, particularly in the morning. Carskadon found that if teenagers are able to sleep as much as they want, they average about nine and a quarter hours. She now believes that teens should get at least eight and a quarter hours of sleep each day. The problem with most adolescents is that they never get enough. Many operate in a constant state of sleep deprivation.

Since adolescence is a time when most teens are driven by a desire to assert their independence, they equate later bedtimes with adulthood. This desire may have been fuelled for years by parents who used early bedtimes as a punishment and permission to stay up late as a reward. Besides, all types of diversions keep teens up late: part-time jobs, homework, all-night television, computers and the Internet.

The problem is that if their wake up time is not pushed ahead, which rarely happens, teens miss out on an essential phase of sleep, the final phase of dreaming or Rapid Eye Movement (REM) sleep, which is essential for that feeling of a good night’s sleep. Going to bed an hour earlier doesn’t work, since teens can’t change their circadian rhythm. If they go to bed an hour earlier they will probably spend the time staring at the ceiling.

There are many side effects for teens who do not receive that extra sleep in the morning. Their reaction times are slowed considerably. This factor has been linked to countless car accidents. It is also why most athletes are told to get a good night’s sleep before a big game. Sleep deprivation also affects cognitive functioning, especially divergent thinking, which is needed for creative problem solving or answering essay questions.

Dahl’s research has found that sleep deprivation leads to emotional and behavioural problems. During adolescence, parts of the brain shift to more adult characteristics such as making long term goals and waiting for gratification. Eventually these replace less mature areas of the brain that lead children to emotional outbursts and temper tantrums. This is made possible by what researchers call cross-temporal processing, where we remember the past to help us decide the best course of action in the future. For example, a child who is sent to his room for not sharing with a friend may decide that sharing is the best course of action. Dahl believes teens who are sleep deprived are less likely to suppress childlike emotions. He says, "It’s dangerous to generalize, but there are a large number of teens for whom a simple lack of sleep may really tip the balance for having emotional difficulties."

Several other researchers have found that sleep deprivation leads to memory loss, impaired information processing, increased irritability, anxiety and depression, decreased socialization and humour, hypersexuality, mental fatigue, reduced memory concentration, increased potential for drug and alcohol use, lower grades and decreased ability to handle complex tasks or to be creative. One 1995 study found that 20 per cent of all high school students fall asleep in school and are accustomed to "a low level of alertness." A 1989 study found that half of the students surveyed reported being most alert after 3 p.m.

This growing body of research suggests the delayed melatonin surge in teens means they desperately need to sleep past 7 a.m. Carskadon believes that early school starting times result only in grogginess, lack of attention, poor performance on exams and increased chances of behavioural and discipline problems. "Kids are waking up and going to school at a time when their brains are still in the nighttime mode," Carskadon says. "Even in the second period, they are not ready to learn, not ready to be engaged in education."


To remedy this problem, 16 school districts in Minnesota began experimenting with changes in school start times. The results are impressive. School officials in Edina changed their start time from 7:20 to 8:30. "Previously, 20 per cent of these kids were sleeping during the first hour of school," says school administrator Kyla Wahlstrom. "Now none are. They are participants instead of zombies."

Administrators received fewer referrals for discipline problems, and the number of students reporting depression or illness dropped dramatically. Student scores were higher than in previous years for Grades 11 and 12. Many teachers agreed that they did not have as many students with "their heads down on the desk, they seem to be more engaged in what they’re doing, they seem to be more focused." Most administrators noted that the halls just seemed to be calmer. They believed the later start time seemed to have a positive impact on the overall atmosphere in the school.

Generally, teachers came to school at the same time, but used the first hour for meetings or to prepare for classes. Parents were also happier with the later start time. One teacher polled the parents of her 160 students to determine if they saw a change in behaviour. She discovered it was an overwhelming "yes" particularly with behaviour and attitudes.

Another district decided to offer a two-tiered system where students could choose between start times of 7:30 or 8:30. Only one third of the student body chose the earlier start time. This corresponds exactly with sleep research, which has found that 30 per cent of the population are naturally "larks" or morning people.

This individual need for sleep is a mystery that continues to baffle scientists. Dahl explains that while some people can get by with as little as four and a half hours of sleep, others desperately need nine hours. Only five per cent of adults can function well on less than six. Each person also has a different peak time. Dahl says, "Some have no problem getting up early in the morning while others are inexplicably but unquestionably night people and look upon dawn with Dracular dread." Sleep researchers refer to them as larks and owls.

Experts generally agree that newborns need to sleep about 18 hours. Toddlers and young children need about 12. Children from age eight up to the late teens need eight and a quarter to nine and a quarter hours each night. Older teens need to fall asleep later and sleep longer in the morning. The average adult needs about eight and a quarter hours.

Unfortunately, it is not only teenagers who are walking around in a constant state of sleep deprivation. Sleepless nights have become an epidemic for two-thirds of the population. Sleep disorder clinics are popping up everywhere. William Dement of Stanford University estimates that 24,000 Americans die in accidents caused by sleeplessness every year.

This all goes back to 1879 when Edison perfected the light bulb. With light and the ability to read late into the night, radio, television, all night stores and the Internet we have altered our circadian rhythms. In 1910 most people averaged nine hours of sleep a night. Today it has dropped to seven.

Stanley Cohen in his 1996 study, Sleep Thieves, wrote that since "apes and monkeys sleep 10 hours or more each day, we might conclude that human beings are sleeping around two-and-a-half hours less than they should." This is not surprising, since the sleep-wake cycle of apes is closest to humans.

So don’t despair if you need eight to 10 hours of sleep. Many sleep researchers have found that creative people and problem solvers often need more.

You are in good company. It was through a series of dreams that Albert Einstein formed his theory of relativity. Apparently, Einstein wandered into work at mid-morning every day after receiving his daily quota of 10 hours of sleep.

Perhaps those 12 students who are chronically late for their first period class are doing their own form of research.

Marina Quattrocchi, an owl, teaches English at St. Augustine Secondary School in Brampton. She has also taught elementary school. She can be reached at marina.quattro@sympatico.ca