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As any parent knows, an exhausted child is an ill-behaved one. So it’s no surprise that a new study finds that young children who snore persistently — which can disrupt the quality of their sleep — are more likely to have behavioral problems like hyperactivity, depression and inattention than kids who don’t snore.

“A lot of kids snore every so often, and cartoons make snoring look cute or funny. But loud snoring that lasts for months is not normal,” said lead author and neuropsychologist Dean Beebe of the Cincinnati Children’s Hospital Medical Center in a statement, “and anything that puts young kids at that much risk for behavioral problems is neither cute nor funny.”

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Previous studies have associated persistent snoring with new or worsening behavior problems in older children, but the authors of the new research say the effects of chronic snoring haven’t been studied in very young children until now, even though symptoms of sleep-disordered breathing spike at about age 2 or 3.

“Care decisions for preschool-aged children who snore are based on guidelines developed largely for older children,” the authors write, noting that doctors must resort to weighing the real, if rare, risks of such interventions as surgery to remove tonsils and adenoids (enlargement of which often causes snoring) against the suspected but unknown risks associated with snoring.

The current study, published Monday in Pediatrics, seeks to clarify some of those risks. Researchers tracked 249 children and their mothers, who were enrolled in an ongoing study of children’s health beginning in 2003 when the mothers were still pregnant. When their children were aged 2, and again when they were 3, the mothers completed questionnaires about the kids’ snoring and behavior.

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Most children (170, or 68% of the group) were classified as non-snorers; their mothers reported them snoring only rarely at both age 2 and 3. Fifty-seven kids (23%) fell into the “transient” snoring category, snoring loudly at least twice a week at either age 2 or 3, but not at both time points. And a smaller number of children (22, or 9% of the group) snored persistently, two or more times a week at age 2 and 3.

The researchers found that the persistent snorers had significantly worse behavior, particularly when it came to hyperactivity, attention and depression, than non-snorers or transient snorers — an association that remained even after the authors adjusted for other factors like gender, race and socioeconomic status.

Thirty-five percent of persistent snorers showed “at risk” behavior, compared with 10% of non-snorers and 12% of transient snorers, the study found.

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“Snoring can disrupt the quality of sleep, and a tired toddler has a much lower tolerance for frustration. When you add chronicity to the problem, over time, that lack of sleep sets up negative interactions within the toddler’s environment, which may change the way they respond,” Beebe told HealthDay. “This is a developing brain. The connections that are made and retained are about their experiences. A lack of sleep could fundamentally alter those experiences.”

As in previous studies of older children, the researchers didn’t see differences in intellectual or motor development in 2- or 3-year-olds based on snoring. Also, because of the study’s observational design, the researchers couldn’t definitively say that snoring caused kids’ behavior problems, only that there was an association.

The study did identify certain predictors of persistent snoring, however: snorers were more likely to be African American and of low socioeconomic status. Further, among the non-African American children in the study (94% of whom were white), snorers were more likely to be exposed to secondhand smoke.

Another strong predictor of snoring: how long kids were breast-fed. None of the children in the study who were breast-fed for more than 12 months developed persistent snoring, but nearly a quarter of those who were never breast-fed or who nursed for less than a month became chronic snorers. Again, the associations held up after the researchers controlled for confounding demographic factors.

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The researchers note that previous studies have also linked breast-feeding to risks of sleep-disordered breathing, finding that kids who were nursed longer between 2 and 5 months of age were less likely to develop sleep apnea. It’s not clear why that’s so, but scientists have suggested that breast-feeding helps babies develop healthy upper airway structures and that breast milk may offer immune protection against infections that encourage sleep-disordered breathing.

Based on their findings, the authors urge pediatricians to screen preschool-age children for loud, chronic snoring, especially in poorer or black families. “Failing to screen, or taking a ‘wait and see’ approach on snoring, could make preschool behavior problems worse,” said Beebe. “I encourage parents to talk to their child’s doctor about loud snoring, especially if it happens a lot and persists over time.”