CU-Boulder study finds some toddlers may be biologically opposed to early bedtimes


(Credit: Zach Ornitz/University of Colorado)

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BOULDER, Colo. — This may not come as news to parents of toddlers, but a new study found that some young children may be biologically opposed to going bed before they’re ready.

The blame, said CU-Boulder assistant professor Monique LeBourgeois, lies with the so-called body clock governed by the hormone melatonin.

Basically, a rise in melatonin levels signals the body that it’s time to go to sleep. It’s well-documented that adults can have different hormone cycles, which affect when the person feels ready to go to sleep and wake up.

But there are not many similar studies for children.

“There is relatively little research out there on how the physiology of toddlers may contribute to the emergence of sleep problems,” said LeBourgeois, who led the study. “Sleeping at the wrong ‘biological clock’ time leads to sleep difficulties, like insomnia, in adults.”

The bedtime you select for your toddler may be out of sync with his or her internal body clock, the study of 14 toddlers suggests. This could contribute to difficulties for youngsters attempting to settle in for the night.

The average evening melatonin onset for toddlers in the study occurred at 7:40 p.m., which is about 30 minutes before parent-selected bedtimes, said LeBourgeois. On average, the toddlers fell asleep about 30 minutes after bedtime.

“It’s not practical to assess melatonin levels in every child,” LeBourgeois said. “But if your child is resisting bedtime or having problems falling asleep, it is likely he or she is not physiologically ready for sleep at that time.”

The findings are important because about 25 percent of toddlers and preschoolers have problems settling after bedtime, LeBourgeois said. Evening sleep disturbance can include difficulties falling asleep, bedtime resistance, tantrums, and “curtain calls” — coming out of the bedroom, often repeatedly, for another story, glass of water or bathroom trip, she said.

Sleep problems in early childhood are predictive of later emotional and behavioral problems, as well as poor cognitive function, that can persist into later childhood and adolescence. In addition, parents of young children with sleep problems often report increased difficulties in their own sleep patterns, which can cause chronic fatigue and even marital discord, she said.

A paper on the subject was published this month in the journal Mind, Brain and Education. Co-authors included University Children’s Hospital Zurich Director of Child Development Oskar Jenni and CU-Boulder Associate Professor Kenneth Wright Jr. The National Institute of Mental Health funded the study.

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