A new US study has found that lack of sleep in children aged 9 to 12 is linked to increased risk of being overweight.
The study is published in the 5th November issue of Pediatrics and is the work of Dr Julie C Lumeng, assistant research scientist at the University of Michigan Center for Human Growth and Development, Ann Arbor, Michigan, and colleagues.
The researchers were working on a project called Sleep ImageIn that explored the link between sleep duration in third and sixth grade children and their risk of being overweight.
“Many children aren’t getting enough sleep, and that lack of sleep may not only be making them moody or preventing them from being alert and ready to learn at school, it may also be leading to a higher risk of being overweight,” said Lumeng.
Scientists have already shown that adults who do not get enough sleep are at increased risk of obesity. Other researchers in Japan and the UK have shown there is a link between insufficient sleep and being overweight in childhood, but those studies did not rule out race and socioeconomic status said Lumeng, who is also assistant professor in the Department of Pediatrics and Communicable Diseases at the University’s CS Mott Children’s Hospital.
Lumeng and colleagues found that children who slept for fewer than 9 hours a day were at increased risk of being overweight, and this was unaffected by sex, race, socioeconomic status, or quality of their home environment.
Among the sixth graders, those who slept the least were the most likely to be overweight, and among the third grade children, those who slept the least were most likely to be overweight in sixth grade, regardless of their BMI (body mass index, a measure of obesity that relates body weight to height) in third grade.
Lumeng said it was important to ensure that children get enough sleep, “primarily through enforcing an age-appropriate bed time”.
The researchers looked at the data on reported sleep problems, sleep duration and BMI for 785 children aged 9 to 12. Half of the participants were male, 81 per cent were white, and 18 per cent of those in the sixth grade were overweight. The records were from the National Institute of Child Health and Human Development Study of Early Child Care and Youth Development.
They found that sixth grade children who were overweight slept less than children who were not overweight and most of the overweight sixth graders were boys.
While boys reported sleeping fewer hours, girls reported more sleep problems. However, sleep problems were not linked with being overweight.
On a more optimistic note, the study found that every extra hour of sleep in the sixth grade was linked to a 20 per cent reduction in risk of being overweight in the sixth grade, while in the third grade this was linked to a 40 per cent reduction in being overweight in the sixth grade.
Speculating on their findings Lumeng said that “sleep may have a behavior impact on children”.
It could be the case that children who get enough rest have more energy to exercise, said Lumeng, for instance they may go out and play instead of lying around watching TV. And perhaps “when children are tired, they may be more irritable or moody, and may use food to regulate their mood,” she added.
However, there could also be a biological reason, because new research is beginning to show links between disrupted sleep and hormones that control the storage of body fat, appetite and the metabolism of glucose, said Lumeng.
Insufficient sleep changes the way the body uses carbohydrates, leading to changes in glucose tolerance, which can affect weight. Day and night rhythms are also known to affect glucose and insulin levels. Levels of leptin, a hormone that helps to control appetite and metabolism, are also affected.
Noting that the links between leptin and sleep is an area of research for which more evidence is required, Lumeng said that:
“Weight gain may not be a result of sleep’s effect on behavior, but rather sleep’s effect on hormone secretion in the body, specifically, leptin and grehlin.”
Grehlin (or ghrelin) is another hormone that works with leptin to control appetite and the feeling of fullness.
Lumeng and colleagues said that the bottom line is:
“If families are struggling to get their children to go to sleep at a reasonable hour, they should seek help from their health care provider.”
“Revising school start times may also provide a solution to increasing the amount of sleep a child gets each day,” they added.
According to the National Sleep Foundation, preschoolers should get 11 to 13 hours sleep a night, elementary school kids between 10 and 12 hours, pre-teens 9 to 11 hours, and teenagers should get 8.5 to 9 hours of sleep a night.
“Shorter Sleep Duration Is Associated With Increased Risk for Being Overweight at Ages 9 to 12 Years.”
Lumeng, Julie C., Somashekar, Deepak, Appugliese, Danielle, Kaciroti, Niko, Corwyn, Robert F., Bradley, Robert H.
Pediatrics Vol. 120 No. 5 November 2007, pp. 1020-1029.
doi:10.1542/peds.2006-3295
Click here for Abstract.
Click here for University of Michigan CS Mott Children’s Hospital.
Written by: Catharine Paddock