An extra hour's sleep each night can slash a preschooler's risk of obesity, according to Growing Up in New Zealand (GUNZ) research.

Researchers of our country's largest longitudinal study of child development have found sleep is crucial to protecting those already "at-risk" from becoming overweight.

Countless Kiwi parents wrestle with their children's sleeping habits each night, and getting preschoolers off to bed, particularly given our scorching hot summer.

The GUNZ researchers identified "at-risk" youngsters using nearly 20 categories, including whether children lived in poverty or were from families experiencing financial stress which could lead to purchasing low-cost but nutrient-poor foods.

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Lead author, Dr Samantha Marsh from the University of Auckland's National Institute for Health Innovation, told the Herald it was already known that children could maintain a healthy body weight despite being exposed to a range of obesity risk factors.

"We wanted to know why that is. If we could figure that out, then we could look at ways to help children who may be on a pathway to becoming overweight or obese," Marsh said.

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Childhood obesity remains one of the nations biggest public health issues, with one-in-three New Zealand children aged 2-4 years overweight or obese.

The research found an hour's extra sleep could slash vulnerable preschoolers' risk of obesity by 24 per cent.

The Sleep Foundation says preschoolers typically need 11-13 hours' sleep each night.

"As with toddlers, difficulty falling asleep and waking up during the night are common," the foundation's website says.

"With further development of imagination, preschoolers commonly experience night-time fears and nightmares."

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Top tips to keep tot asleep included maintaining a regular and consistent sleep schedule, a relaxing bedtime routine ending in the room where the child sleeps and a consistent sleeping environment which is cool, quiet and without television.

However Marsh didn't want to put a figure on how much sleep children needed, saying different kids needed different amounts.

Researchers of our country's largest longitudinal study of child development found sleep crucial to protecting those already
Researchers of our country's largest longitudinal study of child development found sleep crucial to protecting those already "at-risk" of becoming overweight or obese. Photo / 123RF

Her research into "body weight resilience" tracked 1400 of the 6000 children participating in the GUNZ study, who fitted the criteria for being "at-risk" of becoming obese or overweight.

When these children turned four-and-a-half, parents were interviewed about "resilience" factors - including family routine, sleep, screen use and the family mealtime environment.

These factors were measured against each child's Body Mass Index (BMI) and researchers analysed common trends.

They found that while less screen time and higher quality family meals were important, night-time sleep was crucial, Marsh said.

This was significant because it showed families who faced many of the traditional barriers to health could still take action to help keep their preschool children at a healthy weight.

Massey University's Dr Dee Muller said it was great when preschoolers were able to get sufficient sleep, which lowered their risk of obesity.

"But for me, it really highlights how we need to really be careful that the message isn't that parents need to do better if children aren't sleeping so long," she said.

"There were a number of things going on for the children in the study and what we need to thinking about is what are the political drivers that mean that some children are living in situations where they do have higher risk."

Muller's doctoral research looked at preschooler's sleep and found ethnic and socio-economic inequities in children's sleep duration.

She found that Māori children Māori are twice as likely to have short and inconsistent sleep, and preschoolers living in the most deprived neighbourhoods were four times more likely to have short sleep during the week.

"It's a double edged sword, because we want to get the message out there that sleep is really important for children wellbeing, but also need to be really careful that we're not creating stress by blaming parents if the children aren't sleeping well.

"If we can provide families with the support so that they can support their young children to get the sleep that they need, that's going to really, clearly from this research lower that risk of some really negative consequences."

Marsh said further research was needed to establish the exact relationship between night-time sleep and family organisation.

For now, it was important to focus on how to build long-term healthy sleep routines in preschoolers in a way that was developmentally safe, culturally appropriate and protected the parent-child relationship.

It is 12 years since the study started and the 6000 children, recruited from the greater Auckland, Counties Manukau and Waikato district health board areas, have turned 10 and 11.

OFF TO BED

Mum-of-three Miriam Minnée-Kent said she's been lucky her trio of children are good sleepers, but her and husband Aaron have bedtime rules.

"The oldest one just came out a good sleeper, so I was really lucky in that way and he has set the tone."

Levi, 5, Hope, 4 and two-year-old Asher all sleep in the same room.

"Routine is key, I reckon. They know we've got half and hour of down time before bed, so there's this process of going to sleep."

Miriam Minnée-Kent and Aaron Minnée, with Levi, 5, Hope, 4 and two-year-old Asher. Photo / Supplied
Miriam Minnée-Kent and Aaron Minnée, with Levi, 5, Hope, 4 and two-year-old Asher. Photo / Supplied

The Minnée-Kent children have a sun clock in their room, and are discouraged from leaving bed other to go to the toilet until the sun has risen.

"Usually, they're asleep by eight and awake again between six and six-thirty (in the morning). They usually sleep through the night."

Minnée-Kent said the trio usually fell asleep in 15 - 30 minutes.

As for keeping each other awake, perhaps plotting their escape? She said it doesn't really happen.

"They've grown up with noise. When I first had little people, my mum told me: 'don't keep their rooms and lives quiet'...mum said 'when you were little, I vacuumed in your room while you were asleep'.

Husband Aaron said it was important the kids don't bed-hop at night.

"Never let them sleep in your bed. We haven't done that. Morning cuddles are fine."