As if parents need another reason to enforce their little one's bed times: A new study has found a link between lack of sleep and unhealthy bodyweight.
The report, published in the latest issue of Pediatrics, said young children who skimp on sleep both during the week and on the weekends have a four-fold risk of obesity compared with their more well-rested peers.
Using a special wrist device, University of Chicago investigators tracked the sleep patterns 308 children from Louisville, Ky., between the ages of four and 10 for a week. Before the study the young subjects were identified as normal, overweight, or obese based on their body mass index (BMI) scores, a measure of body fat based on height and weight.
Total sleep time for obese children was more variable on weekends than on school days and they tended to get less catch-up sleep compared with normal and overweight youngsters. Those who got the least amount of sleep overall had a 4.2 times higher risk of tipping the scales in the obese range than other children. When the researchers drew blood samples from a third of the children at random, the heaviest children also had the unhealthiest blood profiles.
Even children who slumbered little during the week but managed to make up for a small portion of missed sleep on the weekends tripled their risk of obesity. This indicates that the children at the heaviest end of the weight range don't seem to be getting as much "catch-up sleep" on the weekends as children with lower BMIs.
"If a child has a tendency to be obese but gets adequate sleep he is more likely to be protected than if he is not sleeping as much as he needs," commented Dr. David Gozal, one of the study's lead researchers and the chair of the pediatrics department at the University of Chicago in Illinois. "Catch-up sleep is better than nothing and can help but we don't think it can offer complete protection."
Prominent sleep researcher Dr. Phyllis C. Zee, the director of the Sleep Disorders Center at Northwestern Memorial Hospital, agreed. "There is growing evidence for a link between sleep duration and childhood obesity. What is new … is that perhaps even more important than sleep duration is the effect of day to day variability of sleep wake timing on weight regulation."
Whether sleep is short, interrupted or disordered, researchers believe that lack of shuteye contributes to a supersized waist line by wreaking havoc on metabolism and the endocrine system -- and this is especially true when the body is young and still growing. Gozal said there are numerous studies where sleep deprivation has been shown to disrupt levels of gherlin and leptin, two hormones which regulate hunger and appetite. When the body craves sleep, it interprets it as hunger causing leptin levels to crash and ghrelin levels to spike; this in turn, seems to trigger overeating and may also signal the body to cling to fat stores more tenaciously.
Other studies indicate that poor sleep can throw off the body's biological clocks -- also known as circadian rhythms -- particularly the clock that regulates glucose and insulin, two hormones that when out of balance, are closely associated with weight gain, heart disease and diabetes. Sleep deficit has also been found to elevate levels of cortisol, a hormone that among other things regulates how the body uses energy; elevated cortisol levels have been linked to insulin resistance and a higher BMI.
Beyond metabolic disruptions, many experts believe that part of the problem is what kids are doing when they're not tucked between the sheets: They're watching TV, playing video games and chowing down on high-calorie junk foods, activities associated with higher childhood obesity rates.
However, not all experts agree that catch-up sleep can help in the fight against childhood obesity. "I'm not sure what definite conclusions can come from a study that lasted only one week but I do think the connection between getting enough sleep and obesity may be there. As far as catch-up sleep on the weekend, other studies have shown the opposite, that you are much better off staying on same schedule including the weekend to keep your circadian rhythms steady and consistent," said Dr. Vicky McEvoy, chief of pediatrics at Mass General West Medical School in Boston.
Gozal said that as a first pass on an important issue, the Pediatrics study is by far the most thorough and extensive to date. "Other studies have only looked at two or three days. This study took place during school year versus summer vacation and reflects the majority of time a child is engaged in typical activities. It's also the first to show an inconsistency between weekday and weekend sleep and we were able to at least pick up suggestion to that effect."
Regardless of weight category, the average child in the study slept eight hours a night during the week – far less than the nine to10 hours recommended by the National Institutes of Health and other health groups. And that's really the take-home message Gonzal wants parents to hear.
"Clearly sleeping is a good healthy proposition and our recommendation is to make every possible effort to have a regular bedtime schedule for your child. Adequate sleep can help reduce obesity as well as other health problems like cardiovascular disease and diabetes now and in the future."