A simple good night's sleep may be one unexpected solution to a major health crisis facing New Zealand - child obesity.
A leading New Zealand researcher in sleep, Sarah-Jane Paine, a senior research fellow at the University of Auckland's Faculty of Medical and Health Sciences, says evidence is increasingly pointing to lack of good quality sleep as a factor for obesity in children under 5.
"The reasons why are not well known," she says, "but we do know preschool kids who have poor sleep are more likely to be heavier than those who get good sleep - and they are more likely to be heavier in later childhood.
"The cost of poor sleep is much greater than many people think and it may have profound consequences for our long-term health."
Paine says she is not sure New Zealanders have fully grasped how significant good sleep is to the health and well-being of children: "If sleep helps give our kids the best opportunities in life then we would be foolish to ignore it."
Her comments come as the Ministry of Health has released sleep guidelines for children under 5 called Sit Less, Move More, Sleep Well. The guidelines say infants, toddlers and preschoolers who regularly sleep less than recommended amounts each day - up to 17 hours for newborn babies - are "at a greater risk of obesity".
It says poor sleep habits in early life are consistently associated with poorer health in later life.
Paine was a member of the report's advisory group while based at the University of Otago Wellington. Part of the Government's Childhood Obesity Plan, it was produced by the ministry and an advisory group of experts on physical activity and child health and well-being and also included guidelines on active play and the use of electronic devices like iPads.
The report - based on an interpretation of key international evidence - says regular physical activity, limited time spent sitting for prolonged periods and an adequate amount of good quality sleep all contribute to better health in young children and reduce the risk of developing obesity.
Obesity in children is a growing problem. The latest New Zealand Health Survey shows 11 per cent or one in nine Kiwi children aged 2-14 are obese, up from 10 per cent at the last survey, while 7 per cent of those aged 2-4 are obese.
A further 21 per cent of children are considered overweight, but not obese. Up to 80 per cent of obese children also suffer the condition as adults.
Paine says more research is needed into the link between sleep and obesity in children but a number of hypotheses exist. "We know in adults poor quality sleep can lead to changes in the hormones dealing with appetite, meaning the body is not getting the biological message it is satiated, and this may be the same with children.
"Not getting enough sleep can create more opportunity to eat and how often as adults do we crave something sweet to eat when we can't sleep at night? Lack of sleep may leave us too tired the next day to burn off the calories, possibly this is the same for kids."
Paine says having a television or other electronic devices in the bedroom can replace some of the time a child spends sleeping.
"There is evidence suggesting reading stories at bedtime sets a child up for a good sleep so it would seem quite sensible to give children an iPad or e-reader," she says. "But there seems to be something about the light emitted from these devices which interferes with sleep promotion systems in the body.
"Perhaps the old-fashioned book is best for this. Studies show children who do not watch TV before bed go to sleep earlier and sleep for longer than those who do."
Paine says sleep is as important a factor in fighting obesity as exercise or nutrition and the new guidelines will give parents and the medical profession a baseline to have conversations around the issue.
The report says only 66 per cent of toddlers (2-year-olds) get the recommended amount of sleep compared to 84 per cent of 3 and 4-year-olds.
"A 2016 study of the relationship between bedtime and obesity found preschoolers who were put to bed after 9pm were twice as likely to become obese by adolescence as those put to bed before 9pm," it says.
In the United States a Harvard Medical School study also links sleep disorder with obesity and other conditions like hypertension and diabetes.
"Research has revealed that people who consistently fail to get enough sleep are at an increased risk of chronic disease," the Harvard study says. "Treating sleep as a priority rather than a luxury may be an important step in preventing a number of chronic medical conditions.
"Several studies have linked insufficient sleep with weight gain. Sleep is now being seen as a potential risk factor for obesity along with lack of exercise and overeating, the two most commonly identified risk factors."
The daily sleep guidelines recommended by the Sit Less, Move More, Sleep Well report are:
• Babies (birth to 3 months) 14-17 hours
• Infants (4 to 12 months) 12-15 hours
• Toddlers (1-2 years) 11-14 hours
• Preschoolers (3-4 years) 10-13 hours