Later bedtimes, after 9pm, appeared to double a child’s chances of suffering from the condition later in life, according to an American study of 977 children.
‘For parents, this reinforces the importance of establishing a bedtime routine,’ said Sarah Anderson (pictured below right), lead author and associate professor of epidemiology at The Ohio State University College of Public Health in Columbus.
‘It’s something concrete that families can do to lower their child’s risk and it’s also likely to have positive benefits on behavior and on social, emotional and cognitive development.’
Previous research has connected short sleep duration and obesity, with one study finding a correlation between late bedtimes and obesity risk five years later.
The new study is the first to use data across a decade beginning in the early years.
The research, published in the The Journal of Pediatrics, used data from 977 children who had taken part in the Study of Early Child Care and Youth Development, which followed healthy babies born in 1991 across ten US locations.
The epidemic of childhood obesity has taken a firm hold in the UK, with 12 per cent of children starting nursery overweight or obese, rising to 22 per cent at reception age, and 33 percent on arrival at secondary school.
By adulthood, the problem can be harder to tackle, leading to health complications such as heart disease.
The academic and her co-authors divided pre-school bedtimes into three categories: before 8pm; 8pm - 9pm, and after 9pm.
The children were aged around four-and-a-half when their mothers reported their typical weekday bedtime.
The researchers linked preschoolers’ bedtimes to obesity when the kids were teens, at an average age of 15.
They found a striking difference: Only ten per cent of the children with the earliest bedtimes became obese teenagers.
That was compared 23 percent of those who went to bed latest, and 16 percent of children with mid-range bedtimes.
Half of the cohort of children had middle category bedtimes, while the remainder were split equally across early and late.
The researchers also looked at the role of ‘maternal sensitivity’ in the outcomes for weight, and found the links were still strong.
Maternal sensitivity factors in the level of support given by the mothers, respect for their child’s autonomy, and hostility.
The children who went to bed latest and whose mothers had the lowest sensitivity scores, faced the highest obesity risk.
Researchers found that later bedtimes were linked to lower income backgrounds and those with poorer education.
The team’s previous research has illustrated the importance of household routines for pre-school-aged children and this builds on that work, they claim.
Assoc Prof Anderson said she and her co-authors focused on bedtimes because they have a greater impact on the duration of sleep than do wake times, over which parents have less control.
When parents and older siblings must get up and out the door early, that often means young children rise early as well.
Putting a child to bed early doesn’t guarantee he or she will fall immediately into a deep sleep, she said, adding that establishing a consistent bedtime routine makes it more likely that children will get the most beneficial amount of sleep.
She claimed that recommending early bedtimes for young children may help to prevent obesity, and paediatricians could help with techniques.
‘It’s important to recognise that having an early bedtime may be more challenging for some families than for others,’ Assoc Prof Anderson said.
‘Families have many competing demands and there are tradeoffs that get made. For example, if you work late, that can push bedtimes later in the evening.’
The majority of young children are biologically pre-programmed to be ready to fall asleep well before 9pm, according to previous research.
Questions not answered by the study concern how sleep time intertwines with a variety of other factors that can contribute to weight gain in childhood, including physical activity and nutrition, which the researchers say is a live area of study.