The connection between insufficient sleep and overweight and obesity in all ages is well recognized and has been demonstrated in multiple studies conducted over the last several years. In the November 2009 issue of Pediatrics, Wing et al* report the results of a study conducted in Hong Kong in which they looked at whether differences in sleeping patterns that allowed school age children to "catch up" on the sleep deficit acquired during the school week had an effect on their becoming overweight or obese. The researchers conducted their study by reviewing questionnaires completed by the parents of 5185 children between the ages of 5-15 in which the parents were asked to comment on what times their children usually went to bed and got up on weekdays, weekends, and vacation during the preceding 12 months. The investigators found that children who slept < 8 hours/night during the week and did not compensate for their sleep deprivation by sleeping in late on weekends or vacation were significantly more likely to be overweight than those who did.
However, there are many problems with this study. Among them: the wide age range of the children (5 year olds have quite different sleep needs and patterns than 15 year olds); the fact that the data collected was based upon a recollection of the typical patterns of an entire year (generating what is known as "recall bias"); and the very small numbers of children in the "non-compensated groups" (38 who did not sleep in on weekends and 29 who did not sleep in on vacations, both each less than 1% of the entire cohort) all make drawing meaningful conclusions from this study very difficult. In fact, when looking at the data of the entire cohort, one sees that the overweight and obese children slept only 6 minutes less on school nights, 9 minutes less on weekends, and 10 minutes on vacation than their non-overweight counterparts.
For all these reasons, it is very difficult to accept the authors' conclusions that children should be allowed to sleep in late on weekends as a means to prevent them from becoming overweight. In fact, there are compelling reasons not to adopt such a strategy. The two main forces which drive our sleep are the sleep deficit, which builds up the longer we remain awake, and the internal circadian clock. When the internal circadian clock is synchronized with the external clock, we start to feel sleepy around our usual bedtime and wakeful around our usual wake up time (provided, of course, that we have gotten enough sleep). However, it is relatively easy to desynchronize the internal from the external clock by shifting sleep onset and wakeup times, exposure to bright light in the evening and/or the morning, the consumption of melatonin. This is especially true for adolescents, who have a natural tendency to "push back" their internal clocks. When the clocks become desynchronized, it becomes quite difficult to fall asleep and to wake up at the appropriate "external clock" times, as anyone who has travelled across time zones and become jetlagged knows all too well.
The last thing a child who is not getting enough sleep during the week because she or he is getting to bed too late needs is to sleep in two, three, or four hours late on the weekend. While allowing the child to "catch up" on some of the lost sleep, it can also decouple the two clocks and make it very difficult for the child to get out of bed on Monday morning in time for school and to really get going before the school day is half gone.
Yes, getting enough sleep is very important, not just for controlling body weight, but for a whole host of other important reasons as well, including good cognitive function, development, school performance, and behavior. But a better solution would be to establish a schedule which gets the child to bed regularly at an hour which allows for an age appropriate amount of sleep, and maintains a regular wake up time on weekdays and weekends. One should also minimize exposure to bright light in the evening, eliminate caffeine at least 8 hours before bedtime, and remove distractions such as television, computers, video games, cell phones media players and pets from the bedroom. Doing all of the above will increase the likelihood of the child getting an adequate amount of sleep, with all the attendant benefits, and without turning weekday mornings into a nightmare for child and parents alike.
*Wing YK et al. The Effect of Weekend and Holiday Sleep Compensation on Childhood Overweight and Obesity. Pediatrics Vol. 124 No. 5 November 2009, pp. e994-e1000
