Researchers from University College London (UCL) analysed the ‘bedtime data’ of more than 10,000 children involved in the UK Millennium Cohort Study at three, five and seven years old.
Alongside the data, they also looked at reports on the children’s behaviour from their mothers and teachers.
They found that at the age of three, children were most likely to have irregular bedtimes, with around one in five going to bed at varying times.
However, the effects of erratic bedtimes on children’s behaviour built up over time.
According to the researchers, as children progressed through early childhood without a regular bedtime, their behavioural scores, which included hyperactivity, conduct problems, problems with peers and emotional difficulties, worsened.
The reason given for this is because irregular bedtimes disrupt circadian rhythms, leading to sleep deprivation that affects the developing brain.
Circadian rhythms are physical, mental and behavourial changes that follow a 24-hour cycle and respond to light and dark.
Professor Yvonne Kelly from UCL’s Epidemiology and Public Health department, said, ‘Not having fixed bedtimes, accompanied by a constant sense of flux, induces a state of body and mind akin to jet lag and this matters for healthy development and daily functioning.
‘We know that early child development has profound influences on health and well-being over a lifetime. It follows that disruptions to sleep, especially if they occur at key times in development, could have important lifelong impacts on health.’
In contrast, the findings also revealed that the effects on behaviour are reversible if children start going to bed at a regular time.
Ms Kelly said, ‘It appears the effects of inconsistent bedtimes are reversible. Children who change from not having to having regular bedtimes show improvements in their behaviour.