In the study, researchers at the University of Michigan Center for Human Growth and Development followed nearly 800 students in grades three through six. They found that elementary school children who got 9.25 hours of sleep per night had an obesity rate of 12.5%. But those who slept fewer than 8.5 hours per night were almost twice as likely to be obese - 23%.
The study was published on the November issue of the journal Pediatrics.
"We found that children who got less sleep were more likely to be obese," said Dr. Julie Lumeng, an assistant research scientist at the University of Michigan center.
The study suggested that there were three likely reasons the lack of sleep affects weight:
- Tired children might be less likely to be active and exercise during the day.
- Tired, irritable children might be more likely to consume junk food to regulate their moods.
- It is possible that there is a connection between sleep and metabolizing fat.
The study followed 785 children from third grade through sixth. Parents were interviewed about their children's sleep habits at the start of the study when children were in third grade, and again when they were in grade six.
To determine the rate of obesity, researchers also measured height and weight of the children. Obesity was defined as having a body mass index higher than the top 5% of children for their age, height and weight. Eighteen percent of children in the study were obese by this measure by the sixth grade.
Researchers took into account demographic data, such as maternal education, race and quality of home environment and parenting skills, to see if those things had bearing on obesity. Regardless of demographics, too little sleep had the most significant correlation.
"Pediatricians and parents really need to start paying closer attention to sleep-wake habits," said Dr. Stephen Sheldon, director of the Sleep Medicine Center at Children's Memorial Hospital in Chicago.
"In this society, we put a premium on being awake, and that premium may hurt us in the long run. Sleep may be as important as food to our health and well-being."
The University of Michigan obesity study appears to reinforce other studies showing that elementary school children need at least 10 hours of sleep per night to achieve optimal health peak school performance.
TIPS FOR CHILDREN
The National Sleep Foundation offers these tips to help parents and schoolchildren get a good night's sleep:
- Keep a regular sleep schedule, and avoid extremes on weekends. Having a regular bedtime increases the likelihood that children - including teens - will get optimal sleep.
- Establish a relaxing bedtime routine. Reading before bed is a good choice for children of all ages and for parents.
- Create a sleep environment that is cool, quiet, dimly lit and comfortable.
- Keep television, video games and other electronics out of the bedroom. NSF's 2006 Sleep in America poll revealed that having electronic devices in the bedroom is associated with an increased risk of falling asleep in class and while doing homework.
- Eliminate exposure to electronic media - television, video and computer games etc. - within an hour of bedtime. Studies show looking into bright lights, such as TV and computer screens, an hour or less before bedtime makes it difficult to fall asleep.
- Limit caffeine, especially after lunchtime.
- Eat well and exercise.
Here are more pointers for parents:
- Be an example. By practicing good sleep habits, your children are less likely to adopt bad ones.
- Talk to your children about the importance of healthy sleep and the consequences of sleepiness, including drowsy driving.
- Recognize that children - including teens - need more sleep than adults.
- Children who have difficulty waking in the morning on more than three days a week or who snore might not be getting adequate sleep and should be evaluated by a specialist.
- Establish a one-hour electronic-free time before bedtime.
- Ask teachers whether your child is alert or sleepy during class and take steps to improve your child's sleep if you feel that he or she may have a sleep problem.
