"Set bedtimes can lead to cleverer children," the Daily Express reports, while BBC News and others report that late nights "sap children's brain power". But looking at the study these headlines are based on, it appears that most of these claims are misleading.
The news comes from a large UK study looking at whether regular bedtimes affect children's reading, maths and spatial ability scores at age seven.
The study found that irregular bedtimes at age three were independently associated with slightly lower cognitive scores at age seven. It also found that in all three tests, girls (but not boys) who had irregular bedtimes at age seven had slightly lower scores than those with regular bedtimes.
The researchers suggest that disrupted sleep patterns may hamper kids' concentration, and that lack of sleep may disrupt the brain's ability to learn.
However, regularity of bedtimes is hard to measure and may be caused by underlying factors, such as a chaotic family life, which may contribute towards lower cognitive functioning.
While the researchers attempted to adjust for these factors (known as confounders), this is unlikely to have completely removed their influence.
Where did the story come from?
The study was carried out by researchers from University College London and was funded by the Economic and Social Research Council.
It was published in the peer-reviewed Journal of Epidemiology and Community Health.
As might be expected, the study was widely covered in the media, with some reports stressing the advantages of set bedtimes. For example, ITV News claimed regular bedtimes could "boost brain power", a headline that is not supported by this study's findings.
The results actually suggest that irregular bedtimes may disrupt the normal pattern of child development – set bedtimes neither "boost" nor disrupt "brain power".
And while most news reports were basically fair, some of the claims overinterpreted the study's results. Researchers tested the children's maths, reading and spatial ability only once. While important, this is hardly a reliable measure of how clever the children were, or of the "power" of their brains.
What kind of research was this?
This was a large cohort study of more than 11,000 seven year olds in the UK. It looked at whether there were any links between regular bedtimes in early childhood and cognitive test scores at age seven.
A cohort study enables researchers to follow large groups of people for lengthy periods, and to study any associations between lifestyle (such as bedtimes) and a particular outcome (such as cognitive test scores). However, on its own it cannot prove a direct cause and effect relationship (causality).
The researchers say that in childhood, reduced or disrupted sleep at key times of development could have an important impact on health throughout life. But most research into sleep and cognitive function has been done in adults and adolescents.
The researchers also say that busy family lives and full-time employment could leave parents and carers feeling as if they do not have enough time with their children. This means there could be an increasing number of parents or carers who delay bedtimes or do not stick to a routine.
What did the research involve?
The researchers used a sample of children from the Millennium Cohort Study. This is an ongoing nationally representative cohort study looking at health outcomes in children who were born in the UK between 2000 and 2001.
Families were visited at home when the children were aged nine months, and three, five and seven years old. During these visits, parents were asked a range of questions about socioeconomic circumstances and family routines.
When the children were aged three, five and seven, their mothers were asked whether they always, usually, sometimes or never went to bed at a regular time on weekdays and during term time. Information about bedtimes at weekends was not collected by the researchers. For five and seven-year-olds with regular bedtimes, researchers also asked what time they went to bed.
At age seven, trained interviewers carried out cognitive assessments of the children. Using established tests, the interviewers assessed three aspects of cognitive performance – reading, maths and spatial ability (the capacity to think about objects in two or three dimensions, such as using a map to navigate).
The researchers conducted two analyses:
- whether the time a child goes to bed and the consistency of his or her routine was associated with performance in tests at the same age (a cross-sectional analysis)
- whether there was any association between test performance at seven and bedtimes at the earlier ages of three and five – this was to see if there was any "cumulative effect" of bedtime on cognitive ability, or if there were "sensitive periods" during early childhood where bedtime is more critical, for example, if a disruption of bedtime routine in early childhood leads to future problems
The researchers created various models to take account of confounders that might influence the results of the study, including:
- child's age
- mother's age
- family income
- educational qualifications of parents
- mother's psychological health
- methods of discipline
- daily activities
- hours spent watching TV or using a computer
The researchers used three types of statistical model:
- model A, which adjusted the results for the child's age
- model B, which adjusted for factors known to have an effect on cognitive development, such as parental education or whether parents read to or tell their child stories daily
- model C, which adjusted the results for factors known to effect quantity and quality of sleep, such as whether a child has a TV in their bedroom
What were the basic results?
The researchers found that irregular bedtimes were most common at age three. At this age, around one in five children went to bed at varying times. By age seven, more than half the children went to bed regularly between 7.30 and 8.30pm.
- At age seven, girls who did not have a regular bedtime performed worse than those who did in tests for reading, maths and spatial ability. This result was found in all three statistical models. The same association was not found in boys of the same age.
- Irregular bedtimes at age three were independently associated with lower reading, maths and spatial ability scores at age seven in both girls and boys.
- Girls who never had regular bedtimes at ages three, five and seven had significantly lower reading, maths and spatial scores at seven years than girls who did have regular bedtimes. For boys, this was the case for those with irregular bedtimes at any two of the ages.
The researchers found that children who had irregular or later bedtimes tended to come from more socially disadvantaged backgrounds.
They were also more likely to have mothers with poor mental health and have more unfavourable routines, such as skipping breakfast or having a TV in the bedroom.
However, time pressures, parental employment and whether parents felt they spent enough time with their child were not associated with later or inconsistent bedtimes.
How did the researchers interpret the results?
The researchers suggest that inconsistent bedtime schedules might affect cognitive development by disrupting circadian rhythms or by affecting the brain's "plasticity" – the ability to acquire and retain information.
They also suggest that the effect is cumulative and that age three could be a sensitive period where cognitive development is affected by late or inconsistent bedtimes. They say girls might be more susceptible to irregular bedtimes than boys.
They also suggest that inconsistent bedtimes during childhood could have knock-on effects throughout life.
They add that policies are needed to better support families to "provide conditions in which young children can flourish".
This was a large nationally representative sample of children who were followed for several years, so the results are more likely to be reliable than small, short studies.
Getting regular sleep is important for children's health, and children require more sleep than adults, so it is not surprising that children going to bed late at age seven also perform worse in mental tests.
Of concern, too, is the suggestion that irregular bedtimes at earlier ages might affect children's mental performance at the age of seven.
However, it should be noted that the study has the following limitiations:
- children were only tested for cognitive ability once
- not having a regular bedtime at three was associated with only a small difference in test scores at seven
- it is possible that other factors, such as social deprivation, affected test scores, although the authors tried to take these into account
- the study relied on parental recall of bedtimes, which might affect the reliability of the reported data
- as the authors point out, direct data on the children's actual sleep quantity and quality was not available – a study recording this could have led to more accurate results
Bedtime routines are important for children. Anyone who has persistent problems getting young children to bed should talk to their GP.
Read more about common sleep problems in children.
Analysis by Bazian
Edited by NHS Website
Links to the headlines
BBC News, 9 July 2013
The Guardian, 8 July 2013
Mail Online, 9 July 2013
The Independent, 9 July 2013
Sky News, 9 July 2013
ITV News, 9 July 2013
Links to the science
Journal of Epidemiology and Community Health. Published online July 8 2013