Sleepless childhoods raise obesity risks

Children who don’t get enough sleep are more likely to be obese when they grow up, the Daily Mail reported on September 22 2007. The report said that research has found that hormones which affect appetite and metabolism are disrupted when we have insufficient sleep.

The research behind this story is from a study of children born in the 1980s in Australia who were monitored from birth until they reached 21. Information given by their mothers on the child's sleeping habits between the ages of 2 and 4 was used to see whether there was any link between their weight as young adults and sleep problems.

This was a large, well-conducted study which shows there is an association between sleeping patterns in childhood and weight as a young adult. However, it does not prove, or aim to prove that the two are directly related.

It is sensible to ensure that children are getting enough sleep, most important, however, is to address the accepted risk factors for obesity such as diet and activity.

Where did the story come from?

Drs Abdullah al Mamun and colleagues from the School of Population Health at the University of Queensland in Brisbane, Australia conducted this research. The study was funded by the National Health and Medical Research Council of Australia. The study was published in the peer reviewed journal, the American Journal of Epidemiology .

What kind of scientific study was this?

The research is an analysis of some of the data collected through a large prospective cohort study that began in Australia in 1981.

The study included over 7,000 women who had given birth at a particular hospital in Brisbane. The women responded to questionnaires when their children were 6 months, 5 years, 14 years and 21 years old. The children also had physical, developmental and cognitive examinations at these times after they were 5 years old. At ages 14 and 21years, the children themselves also completed questionnaires about their health, wellbeing and lifestyle.

In total, the authors analysed data from 2,494 children. They looked at information on the childrens’ sleeping patterns at ages 6 months and 2 to 4 years (from the mothers’ responses to the questionnaire at 5 years). Beyond this age, the childrens’ sleep patterns were not monitored. Information on their height and weight at 21, and data on other factors that may affect weight such as diet, physical activity, and maternal characteristics were also analysed.

The researchers performed several different analyses, using the information collected through the mothers’ and childrens’ questionnaires to determine which childhood factors had contributed to the childrens’ body mass index (BMI) at 21.

What were the results of the study?

The researchers found that the average mean BMI at age 21 increased depending on the frequency of sleep problems between the ages of two and four. In one analysis (which didn’t take into account any of the other potential factors that could affect BMI) young adults were nearly twice as likely to be obese at 21 if they had sleeping problems between the ages of two and four, than those who had no sleeping problems.

In another analysis, which took into account factors such as television watching, diet, maternal BMI etc., young adults were 1.67 times more likely to be obese. There was no link between sleep problems at age 6 months and BMI at age 21 years.

What interpretations did the researchers draw from these results?

The researchers believe that their study provides evidence that a long-term impact of childhood sleeping problems is the later development of obesity. However, they accept that “further research is needed”.

What does the NHS Knowledge Service make of this study?

This large study shows that there is an association between sleep problems in childhood and weight in adulthood. However, it does not prove that the two are directly related and that adult obesity is caused by sleep problems as a child.

Excluding any exceptional circumstances, a common sense interpretation of these results could be that not enough sleep in a 3-4 year old infant is a symptom of a lack of parental control. It could also be argued that childhood obesity, which is mainly caused by bad diet and lack of exercise, also stems from a lack of parental control. We can probably assume that the lifelong influence of a parent upon their child is more likely to affect the childs health as an adult than their sleep patterns in infancy.

Regarding the influence of hormones upon appetite and metabolism as mentioned in the Daily Mail; although previous research may have looked at links between sleep and these hormones, this particular study only looked at sleep problems between the ages of 2 and 4 years, and body mass index at the age of 21 years. A causal relationship that spans the 17 year gap between these events seems unlikely.

Sleep problems may indeed affect lifestyle by reducing energy levels, affecting food consumption, or hormone levels. However, obesity is a condition with many contributing factors. Parents should try their best to ensure that their children get enough sleep and most importantly, that their diet is healthy and physical activity is encouraged. Ultimately, more research is needed before a causal link between sleep problems in childhood and obesity as a young adult can be claimed.

Sir Muir Gray adds...

There are already enough reasons for parents to try to ensure that their children sleep well. This evidence, although highlighting some interesting biological links, is unlikely to persuade parents to try even harder.