Why  is an epidemic of childhood and adolescent obesity sweeping the United States? There is no single answer to that question, but if you are thinking fast food and video games are solely to blame, think again. At least part of the answer may lie in the simple process of sleep. Our kids are getting too little of it.

Consider these older research findings:

  • Texas researchers studied nearly 400 subjects ages 11-16. Those who were obese slept less than those of normal weight did. For each hour of sleep loss, the risk of obesity rose 80 percent. Disturbed sleep was related to diminished physical activity. For every hour spent awake during the night, physical activity during the day declined by 3 percent, which could contribute to gaining weight.
  • Studying more than 8,000 children, Japanese researchers found a strong relationship between late bedtime, short sleeping hours, and obesity.
  • Scientists in Spain found that people who sleep nine or more hours a day were significantly less likely to be obese than those sleeping six hours or less. They found that the risk of obesity increased by 30 percent for every hour of TV watching and decreased by 24 percent for every hour of sleeping.

Now a new study has added additional insights to what's emerging as an impressive body of evidence. In the September issue of Archives of Pediatric and Adolescent Medicine (a JAMA/Archives journal), Janice Bell of the University of Washington and Frederick Zimmerman of the University of California, Los Angeles, report on long-term studies (since 1997) of weight and sleep patterns in nearly 2,000 children. No surprise: they found that 33 percent of the younger children and 36 percent of the older ones were overweight or obese.

But when it came to sleep, the researchers did uncover a few surprises. Specifically, they found that overweight and obesity are associated with nighttime sleep duration (not napping) in two significant ways:

  • Shortened sleep in children under five years of age predicts weight problems later on. "[T]here is a critical window prior to age 5 years when nighttime sleep may be important for subsequent obesity status," say Bell and Zimmerman.

And

  • Short nighttime sleep duration increases the risk of a shift from normal weight to overweight or from overweight to obesity among early teens. In other words, adolescents who sleep less are more likely to pile on the pounds.

Although historical records show that we've grown heavier as our hours of sleep have decreased, experts caution that they can't be sure about the cause-and-effect relationship. Are we overweight because we sleep less, or do we sleep less because we are overweight? Or is some other factor, such as stress or the electric light, promoting both overweight and sleep loss? Until these questions are answered, it makes sense to include a good night's sleep in any plan for weight control--and to establish and enforce a bedtime for children and teens. "Sleep duration is a modifiable risk factor with potentially important implications for obesity prevention and treatment," say Bell and Zimmerman.

What's the best way to modify that risk factor? Put your kids to bed.

How much sleep do children and teens actually need? On average, (your child may need more):
o Toddlers (ages 18 months to 3 years): 12-14 hours in a 24-hour period
o Preschoolers (ages 3-5): 11-13 hours per night
o School children (ages 5 to 12): 10-11 hours per night
o Teens (13-17): 9 or more hours per night

For More Information:

Read about why your brain needs sleep in my book, Brain Sense.

Newest study: Janice F. Bell and Frederick J. Zimmerman. "Shortened Nighttime Sleep Duration in Early Life and Subsequent Childhood Obesity," Arch Pediatr Adolesc Med. 2010;164(9):840-845.

For additional information on sleep, visit the website of the National Sleep Foundation.

Please leave a comment if you would like a list of the older studies cited in this blog.

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