A child sleepingFor many parents of young children, bedtime means tantrums, fits, and requests for just one more glass of water. Why do some kids refuse to go to bed? Research from the University of Colorado Boulder, led by assistant professor Monique LeBourgeois, has found that toddlers fall asleep fastest when their bedtimes are after their body’s nightly melatonin release. The study is the first to explore the connection between toddler physiology and parent-chosen bedtimes. These findings could help kids get to sleep at night and may contribute to understanding how sleep disorders develop.

The researchers enlisted the cooperation of 14 families with toddlers. The children were between the ages of 30 and 36 months. All slept at least 10.5 hours at night and napped for at least 45 minutes during the day. The scientists used saliva samples from the children, taken on one evening every 30 minutes in the six-hours before bedtime. Since light suppresses melatonin production, the families converted their homes into “caves,” covering windows and using low-watt light bulbs. In addition to the melatonin evaluations, the children’s sleep habits were studied for six days.

The results demonstrated that toddlers who had more time between their nightly melatonin rise and bedtime fell asleep faster and they struggled against sleep less. The average melatonin onset time was 7:40 PM, which was around 30 minutes before the parent-selected bedtimes. Toddlers who were put to bed before their natural rise in melatonin took 40 to 60 minutes longer to fall asleep. This could lead to children associating being in bed with wakefulness, which may increase the risk of developing insomnia later on.

Approximately one-quarter of toddlers have sleep-related problems, which can manifest as difficulties falling asleep, bedtime tantrums, or repeatedly getting out of bed before falling asleep. Adjusting a child’s bedtime has the potential to mitigate the challenges of getting a toddler to sleep. Furthermore, sleeping at the “wrong” time according to one’s body can lead to insomnia in adults. Teaching children to work with their own body rhythms could help prevent later sleep disorders.

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

This research is published in the journal Mind, Brain and Education.

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