The Article: Shortened Nighttime Sleep Duration in Early Life and Subsequent Childhood Obesity by Drs. Janice Bell (University of WA, Seattle) and Frederick Zimmerman (UCLA). Arch Pediatr Adolesc Med 2010; 164: 84-845.
Summary: The authors conducted a secondary analysis (meaning they used data already made public to look at something they were interested in) of a US government funded study that, in part, asked families in 1997 and again in 2002 to use time-diaries to record their children's sleep habits. Infants and children in the study were also measured (weight and height) at follow up. The final sample included 822 children who were between 0-59 months and 1108 between 60 to 154 months of age in 1997. They found that children in the younger group (0- 59 mo) with a short duration of nighttime sleep (in the bottom 25%) at baseline had a greater chance of becoming overweight or obese by 2002. This was not found in the older group. Daytime napping did not seem to make a difference.
The Media "Take": I've seen the press coverage from more than 2 dozen news agencies and blogs; most seem to give the impression that infants and children should be sleeping 13 to 14 hours at night in order to reduce the risk for obesity. They don't account for differences in sleep patterns in infancy vs. preschool children.
The Problem: The researchers grouped the children into the 2 groups for statistical and practical purposes (we don't know how many children in the study group were less than 1 year of age) but doing so was not clinically appropriate. I'm sure that the researchers would not say that parents should worry if their newborns sleep less than 10 hours at night. As all of our readers know, newborns and young infants need to wake for many reasons and that while they will sleep a total of 13 or 14 hours, it won't be all at once.
The Reality: The researchers put a whole bunch of kids (from newborns to 4-year-olds) in a big group and found that sleeping more than 10 hours at night was associated with a reduced odds of being overweight later on. Having this "association" does not mean that less sleep causes kids to become heavier. The authors were not able to control for a lot of things that might have made a difference in the children's weight status. More importantly, putting kids with such different expectations for sleep in one big group isn't useful, especially when it confuses parents and reporters. It would have been better to put the infants in a separate group. But of course, the researchers didn't ask me.
I hope this helps you understand this study a little better.
Next time: Back to Twins!
Thank you for explaining the mechanics of the study!ReplyDelete