New Zealand study finds just 39 minutes of sleep can make or break a child's health, happiness and school day

Stock image of a child struggling in class at his desk
After one week of receiving 39 minutes less of sleep per night, the children reported lower overall well-being and ability to cope at school, the study said. Photo credit: Getty Images

By Madeline Holcombe of CNN

One of the keys to keeping your child happy and healthy is making sure they get enough sleep consistently, a new study has found.

That's no surprise to parents, right? But it turns out even 39 minutes can make a difference, the results showed.

In the study published Wednesday in JAMA Network Open, researchers monitored 100 children ages eight to 12 living in New Zealand. The children alternated between a week of going to bed one hour earlier and one hour later - with one week at normal time in between the two.

Then, using a questionnaire, the children and their parents rated their sleep disturbances and impairment during the day. Researchers also administered a survey to the children about their health-related quality of life.

The kids who participated in the study regularly slept between eight and 11 hours a night and were considered generally healthy, the study said.

After one week of receiving 39 minutes less of sleep per night, the children reported lower overall well-being and ability to cope at school, the study said.

"We all know that we feel better with a good night's (sleep) but there is very little data using experimental designs that actually show just (how) big the impact might be," said lead study author Rachael Taylor in an email. "This sort of interventional data is the only way we can 'prove' that changing one behaviour actually does affect another."

The study covered many aspects of well-being, including an assessment of how the children felt physically, and psychologically, in their relationships with parents and peers, and how they felt about school, said Taylor, a research professor of medicine at the University of Otago in New Zealand.

The assessment included questions about whether the kids felt they were able to pay attention at school and felt physically fit, and whether they had energy to have fun and spent time with their friends.

Not all children were able to cut back their sleep the full hour in the study, Taylor said. But whatever amount they reduced caused a decline in their well-being, she said. And the impacts were greater if the study participants lost a half an hour or more of sleep, she added.

"We haven't seen this type of study look at health-related quality of life or quality of life outcomes, which we know are really important because that is often something that really can resonate with families, with teachers, with public health officials, when we're thinking about how important it is to promote healthy sleep," said Ariel Williamson, a paediatric sleep expert in at the Children's Hospital of Philadelphia.

Williamson, who is also an assistant professor of psychiatry and paediatrics at the University of Pennsylvania Perelman School of Medicine, was not involved in the research.

Prioritising sleep

The children in the study were monitored from July 4 to September 1, 2022, and there are still questions regarding the longer-term impacts, Taylor said.

"We don't know what the long term effect might be - maybe children adapt, maybe they don't and their wellbeing worsens even more," Taylor said in an email.

In the meantime, she advised families "not to underestimate the value of sleep and to prioritise sleep as much as is feasible."

It may be easy to brush off a little lost sleep, but getting less good-quality sleep could result in eating more treat foods, worsening school performance and declines in mental health, Taylor added.

And though sound, sufficient sleep is important, it is also crucial to make a plan that is individualised to your family, Williamson said.

Some children with neurodevelopmental differences, such as autism or attention deficit hyperactivity disorder, have variations in sleep needs, for example, or work or activity schedules may make it hard to be in bed as early as you would like your child to be, she added.

If you think your child could benefit from more sleep, Williamson recommends starting out small and even moving bedtime back by 15 minutes.

And quality is as important as quantity. To get more restful sleep, she recommends children have the same bedtime every night (even on weekends), turn off their screens 30 minutes before bed, and follow a bedtime routine, she added.

For some kids, that could mean calming activities that move them toward their bed, but for other children that may mean dancing or stretching to get their bodies ready, Williamson said.

Some families may prioritise the bath, books and bed routine for younger children, but older kids and even adults can benefit from following a schedule that alerts the brain and body it is time to settle in, she said.

"Sometimes I think if we concentrated more on sleep, many other aspects of children's health and wellbeing would be greatly improved," Taylor said. After all, she said, who doesn't like a good night's sleep?