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.