The very best of sleep medicine and research is being presented at the World Sleep Congress in Prague this week. Among that research are findings from work by Child of our Time Editor, Professor Yvonne Kelly and colleagues at the ESRC International Centre for Lifecourse Studies. They have been trying to find out what it is about sleep that matters most when it comes to giving children the best possible start in life. Here Yvonne explains what they have found to date and why regular bedtimes are key to a healthy happy childhood.
What happens in the early years has profound implications for what happens later on in life. Thousands of research papers, many of them using the wonderful rich data in the British Birth Cohort studies, have documented the enduring impacts of the way we live our lives as children on how we fare later on. Children who get a poor start in life are much more likely to experience poor outcomes as adults, whether that’s to do with poor health or their ability to enjoy work and family life later on.
So what has all that got to do with getting enough sleep as a toddler you might ask? Well our research shows it is one of a number of important factors related to getting children off to the best possible start in life and here’s why.
The National Sleep Foundation recommends that toddlers should get around 11 to 14 hours sleep every day. For 3-5 year-olds, the recommendation is 10-13 hours and it suggests 9-11 hours for children once they’re at primary school. But is it all about the number of hours sleep children get, or is there more to it than that? Those are the questions we have been addressing in our research into children’s sleep and how it ties in with how they get on at home and at school across the first decade of their life.
Digging into one of those studies mentioned earlier, the Millennium Cohort Study, which has followed the lives of some 20,000 children since the turn of the century, we found that it’s not just the number of hours a child sleeps that matters, but also having consistent or regular bedtimes.
First we looked at the relationship between regular and irregular bedtimes and how the children got on in a range of cognitive tests. The results were striking. Children with irregular bedtimes had lower scores on maths, reading and spatial awareness tests.
Parents who took part in the MCS were asked whether their children went to bed at a regular time on weekdays. Those who answered “always” or “usually” were put in the regular bedtime group, while those who answered “sometimes” or “never” were put in the irregular bedtime group.
Interestingly, the time that children went to bed had little or no effect on their basic number skills, and ability to work with shapes. But having no set bedtime often led to lower scores, with effects particularly pronounced at age three and the greatest dip in test results seen in girls who had no set bedtime throughout their early life.
The key to understanding all this is circadian rhythms. If I travel from London to New York, when I get to there I’m likely to be slightly ragged because jet lag is not only going to harm my cognitive abilities, but also my appetite and emotions. That’s for me, an adult. If I bring one of my children with me and I want them to do well at a maths test having just jumped across time zones, they will struggle even more than I will. The body is an instrument, and a child’s is especially prone to getting out of tune.
The same thing happens when children go to bed at 8 p.m. one night, 10 p.m. the next and 7 p.m. another — we sometimes call this a “social jet lag effect.” Without ever getting on a plane, a child’s bodily systems get shuffled through time zones and their circadian rhythms and hormonal systems take a hit as a result.
Bedtimes and behaviour
Having established the importance of sleep to a child’s intellectual development, we turned our attention to the relationship between regular bedtimes and their behaviour.
At age 7, according to parents and teachers, children in the MCS who had irregular bedtimes were considerably more likely to have behaviour problems than their peers who had a regular bedtime. In addition, the longer a child had been able to go to bed at different times each night, the worse his or her behaviour problems were. In other words the problems accumulated through childhood.
One really important piece of good news was that we found that those negative effects appeared to be reversible, so children who changed from not having to having regular bedtimes showed improvements in their behaviour. There seems to be a clear message here that it’s never too late to help children back onto a positive path and a small change could make a big difference to how well they get on. Of course, the reverse was also true so the behaviour of children with a regular bedtime who switched to an irregular one, worsened.
Bedtimes and obesity
In a follow up study, which looked at the impact of routines including bedtimes on obesity, we reported that children with irregular bedtimes were more likely to be overweight and have lower self-esteem and satisfaction with their bodies.
In fact, of all the routines we studied, an inconsistent bedtime was most strongly associated with the risk of obesity, supporting other recent findings which showed that young children who skipped breakfast and went to bed at irregular times were more likely to be obese at age 11.
Even children who ‘usually’ had a regular bedtime were 20 per cent more likely to be obese than those who ‘always’ went to bed at around the same time.
So we have a body of robust evidence now that shows very clearly that regular bedtimes really matter when it comes to a child’s health and development over that important first decade of their life.
Providing that evidence in the form of advice to parents and all those caring for young children alongside recommended hours of sleep could make a real difference, helping protect our children from ‘social jet-lag’ and getting them off to a flying start instead.
- Download Yvonne’s slides from the World Sleep Congress –Sleep and child development: findings from the Millennium Cohort Study
- Changes in Bedtime Schedules and Behavioral Difficulties in 7 Year Old Children is research by , ,
- Time for bed: associations with cognitive performance in 7-year-old children: a longitudinal population-based study is research by , ,
- Self-regulation and household routines at age three and obesity at age eleven: longitudinal analysis of the UK Millennium Cohort Study is research by Sarah Anderson,