"Regular bedtimes make children less likely to be obese as adults," is the slightly misleading Mail Online headline. This follows a study looking at the link between household routines in early childhood and obesity at age 11.
Researchers analysed data about children in the UK that had been collected as part of a previous large study (the UK Millennium Cohort Study).
Parents were asked questions about their child's routines at three years of age, including whether they had a regular bedtime. The children then had their height and weight measured at age 11 to see if they were obese.
The study looked at whether there was a link between obesity at age 11 and certain routines earlier in life. They found young children with an inconsistent bedtime were almost twice as likely to be obese aged 11 as those with a regular bedtime.
But this doesn't prove an irregular bedtime directly causes obesity by itself. It could be that children with irregular bedtimes are more likely to have a less healthy lifestyle overall. For example, they may have a poorer diet and exercise less – neither of which was measured in this study.
Also, the parents in the study weren't asked how much sleep the child actually got, which is likely to be an important factor.
Overall, this study alone doesn't prove that an irregular bedtime during childhood directly increases the risk of later obesity.
Where did the story come from?
The study was carried out by researchers from The Ohio State University College of Public Health, Temple University, Philadelphia, and University College London. Funding was provided by the National Institutes of Health and the UK Economic and Social Research Council.
The study has been accepted for publication by the International Journal of Obesity. However, it has not yet gone through the full review process, so some further changes could be made ahead of the final publication.
Despite the Mail Online saying regular bedtimes make children less likely to be obese "as adults" the study only went as far as 11 years of age.
Media reports also claimed the study found that watching lots of TV was linked to a higher risk of obesity, but the researchers actually found no link between the two after several other factors had been taken into account.
In general, the media stories might have benefitted from considering the other limitations to this research, notably the fact that other environmental and lifestyle factors could have influenced the results.
What kind of research was this?
This was a cohort study that used data collected as part of the ongoing UK Millennium Cohort Study to see whether household routines when a child is three, such as sleep times and meal times, are linked with child obesity at the age of 11.
As the researchers say, young children benefit from regular routines and a previous study has suggested that this is likely to help them regulate their behaviours as older children and adults. However, no previous studies have looked at whether household routines and self-regulation are linked with later obesity.
The main limitation with this study is that although it can find links, it is very difficult to pin down a single cause, such as sleep, to a general health outcome like obesity. It is most likely that obesity is influenced by a variety of environmental and lifestyle factors.
What did the research involve?
The study used data collected as part of the UK Millennium Cohort Study (MCS), which in 2000-2002 recruited 19,244 nationally-representative families with a baby aged nine months in the household. A first home assessment was carried out when the child was nine months, followed by repeat assessments at three, five, seven and 11 years of age.
When the child was aged three household routines were assessed. This included asking parents whether the child went to bed at regular times or ate meals at regular times. Those who replied "always" were said to have regular routines, while those who replied "sometimes" or "never" were regarded as inconsistent.
Child self-regulation was also assessed at age three using the Child Social Behaviour Questionnaire. Parents were asked to reply "not true", "somewhat true", "certainly true" or "can't say" to questions around child emotions (such as whether they're easily frustrated) and cognitive self-regulation (for example, whether they persist with difficult tasks).
At age 11 the child's height and weight were measured to see if the child was obese. The researchers modelled the links between child sleep and self-regulation aged three and obesity aged 11. They took account of various potential confounders that could be having an influence, such as ethnicity, parent's age at child's birth, educational level, household size and income.
The final sample included 10,995 children who had full assessment data available.
What were the basic results?
At the age of three 41% of children always had a regular bedtime, 47% had regular mealtimes, and only around a quarter (23%) were restricted to viewing no more than one hour of TV a day. At age 11, 6.2% of children were obese. Obesity was more common in families with lower educational level and lower household income.
Having regular bed and meal times and limited TV viewing were all linked with better emotional regulation, but only regular meal times were associated with better cognitive regulation.
When adjusted for all confounders, children with inconsistent bedtime at three years of age were almost twice as likely to be obese aged 11 (odds ratio 1.87, 95% confidence interval 1.39 to 2.51). Poor emotional regulation was also linked with increased risk (OR 1.38, 95% CI 1.11 to 1.71).
TV viewing wasn't linked with risk of obesity and, interestingly, children with inconsistent mealtimes were actually less likely to be obese.
How did the researchers interpret the results?
The researchers conclude: "Three-year-old children who had regular bedtimes, mealtimes, and limits on their television/video time had better emotional self-regulation. Lack of a regular bedtime and poorer emotional self-regulation at age 3 were independent predictors of obesity at age 11."
This study aimed to look at whether child routines and behavioural regulation are linked with child obesity aged 11. The study made use of data collected at regular home assessments for a large, nationally representative UK sample.
The data suggests that inconsistent bedtimes are linked with increased likelihood of the child being obese at age 11. But before drawing firm conclusions about this, there are a couple of points to bear in mind.
- Though the researchers have tried to adjust for sociodemographic factors, there is a high possibility that this link is being influenced by confounding factors. The most likely confounding factors apparently missing from the analysis are diet and physical activity. It could be that inconsistent bedtimes are linked with less healthy lifestyle patterns in general, and together these all contribute to risk of obesity. It's very difficult to accurately blame a single factor such as sleep.
- Sleep routines weren't assessed in much depth. Parents were only given very brief options when asked if their child has regular bedtimes – "always", "usually", "sometimes" or "never". It's not always possible to be accurate and these responses may mean different things to different people. It also gives no indication of the duration or quality of the child's sleep.
- This study doesn't include any analysis of how the child's sleep patterns or behaviour have changed between three and 11 years of age. For example, the child may have been having problems with behaviour and difficulties going to bed around the age of three but this may have settled down in the years since.
- Obesity has only been assessed at 11 years of age. This doesn't tell us whether the child is going to be obese in later adolescence or adulthood.
Overall this supports understanding that it can be helpful for young children to have regular routines. But this study provides no proof that if a child doesn't have a regular bedtime, this will directly increase their risk of later obesity.