Young children who snore a lot or have other breathing problems at night may have a heightened risk of behavioral and emotional problems later in life, according to a US study of more than 10,000 children.
The study, published in the journal Pediatrics, is not the first to link behavioral issues to so-called sleep-disordered breathing - where children chronically snore, mouth-breathe or seem to stop breathing for seconds at a time, known as apnea.
"We didn't invent the association," said lead researcher Karen Bonuck, at New York's Albert Einstein College of Medicine.
But the work by her team, which followed more than 13,000 children from infancy to the age of seven, is the largest study yet to examine the issue, she added.
Of those children, 45 per cent remained free of nighttime breathing problems, according to reports from parents. The rest had symptoms at some point during infancy or early childhood.
Eight per cent of the children fell into what researchers dubbed the "worst case" group, with breathing problems that peaked between the ages of two and three, and then persisted.
Overall, Bonuck's team found, children with sleep-disordered breathing at any time were more likely to develop symptoms of behavioral or emotional disorders, such as attention deficit hyperactivity disorder (ADHD) or anxiety, by age seven.
About 13.5 per cent had such symptoms at age seven, versus just over eight per cent of children who'd been free of sleep-disordered breathing.
The biggest risk was seen in the worst-case group. By age 7, nearly 18 per cent of those children had possible behavioral or emotional disorders.
The researchers couldn't say for sure whether all of those children had outright disorders, such as ADHD, since their results are based on a screening questionnaire given to parents. The children would have to be further evaluated to get a diagnosis, Bonuck said.
In addition, it's not certain that the breathing problems are directly to blame.
But Bonuck said the researchers did factor in a range of variables that could help account for the link, such as parents' income and education, race, birth weight and whether their mothers smoked during pregnancy.
"Even considering all those variables, overall, sleep-disordered breathing seemed to have the strongest effect," Bonuck said.
Among the worst-case children, for example, sleep-disordered breathing was linked to a 72 per cent increase in the risk of behavioral and emotional symptoms at age seven, even with other factors considered.
Bonuck stressed that nobody is saying that sleep-disordered breathing is the whole story and advised parents not to panic.
"Certainly, emotional and behavioral disorders are multi-factorial," she added.
"But parents can pay attention to their child's breathing, and if they have a concern, they should ask their pediatrician about it."