Monday, October 4, 2010

The Lost Hour

“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. . . . Even kindergartners get thirty minutes less a night than they used to.”

Chapter 2 of NurtureShock "The Lost Hour,” explores in depth and with significant research the effects of this sleep loss on children’s and teenagers’ academic performance, cognitive abilities, and moods and coping skills. There is also growing evidence that lack of sleep may contribute to childhood obesity.

The first part of this chapter considers the impact of sleep on elementary-aged children. One of the most compelling reasons for children to get enough sleep is that their brains “are a work in progress until the age of 21,” and much of that growth and development takes place while children are sleeping. Not only that, but children’s sleep is qualitatively different from adults’ sleep. Sleep scientists have found that children spend 40% more time asleep in the slow-wave state (10 times the proportion that adults spend) during which the brain stores what it has learned during the day, especially vocabulary, times tables, dates, and other factual information and synthesizes memories and makes new associations that lead to “new insights the next day.” Children process what they learn in the daytime while they sleep. And, as the authors emphasize, the intensity of what children are expected to learn today has increased greatly from 10 to 20 years ago.

The second part of this chapter explores teenagers’ need to sleep longer in the morning and argues convincingly that high schools should start an hour later. Why? Two things happen: Adolescents’ circadian systems or biological clocks do a phase shift that keeps them up later, and their brains produce melatonin (a hormone that makes us sleepy when it gets dark outside) 90 minutes later than it does in prepubescents and adults. Therefore, teenagers’ brains are still releasing melatonin when their alarm clocks go off early in the morning. In fact, this is one of the reasons that teenagers are “responsible for more than half of the 100,000 ‘fall asleep’ crashes annually.” It’s hard not to be convinced of this research when one study showed a stunning rise in SAT scores when students had an extra hour of sleep and students themselves reported higher motivation levels and lower levels of depression.

The last part of this chapter examines the recent research on childhood obesity and sleep. It’s no surprise that the less sleep children get, the less active they are during the day. However, Dr. Eve Cauter has discovered that sleep loss “increases the hormone ghrelin, which signals hunger, and decreases its metabolic opposite, leptin, which suppresses appetite.” Scientists are finding a link between “getting fatter” and “getting less sleep.” The several studies the authors cite are quite convincing.

This chapter on sleep, however, does not offer advice on how much sleep children should get each night. After consulting several websites (,,, and an article in KidsPost) there is a general consensus that children ages five to 12 years old should get 10 to 11 hours of sleep a night. Children ages 12 to 18 should get eight to nine hours of sleep a night. And children ages three to six should get 10 to 12 hours of sleep a night.

Here are five findings to consider from this chapter:

  • A loss of one hour of sleep is equivalent to [the loss of] two years of cognitive maturation and development (page 32). In other words, a slightly sleepy sixth-grader will perform in class like a mere fourth-grader.
  • There are significant academic consequences of small sleep differences.
  • Tired children can’t remember what they just learned because neurons lose their plasticity, becoming incapable of forming the new synaptic connections necessary to encode a memory.
  • Sleep-deprived people fail to recall pleasant memories, yet recall gloomy memories just fine.
  • The Centers for Disease Control now recommends that high schools consider later starts. CDC representatives support the idea that a change in school start times can change lives.
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1 comment:

  1. I enjoyed reading your article :) PLease continue publishing helpful topics like this. Regards, from beddingstock.