Researchers found that two- and three-year-olds who snored loudly at least a couple of times per week tended to have more problems with inattention and hyperactivity.

More than one-third of those "persistent" snorers were considered to be at least at risk of a behavioral disorder, like attention-deficit hyperactivity disorder (ADHD).

That compared with 10 percent to 12 percent of their peers who either did not snore or had shorter-lived problems.

The study, published in the journal Pediatrics, adds to others that have linked children's behavior to so-called sleep-disordered breathing - when kids chronically snore, mouth-breathe or seem to stop breathing for several seconds at a time as they sleep (what doctors call "apnea").

The findings do not prove that the breathing problems directly lead to behavioral problems - or that treating the underlying cause of snoring can improve kids' behavior.

But they suggest that problem snoring is something parents and pediatricians should take seriously, according to lead researcher Dean W. Beebe, of Cincinnati Children's Hospital Medical Center.

"Kids are going to snore sometimes, especially when they have a cold," Beebe said in an interview. "It's when the snoring persists that it gets concerning."

Chronic, loud snoring, he said, "should be on parents' radar, and it's something they should bring up to their pediatrician."

The American Academy of Pediatrics already recommends that pediatricians ask parents about kids' snoring, in order to catch cases of sleep-disordered breathing. But in real life, that may or may not happen, Beebe said.

For many kids, especially three- to six-year-olds, loud snoring is caused by enlarged tonsils or adenoids, and removing the tissue can improve their ability to breathe at night.

Another treatment option is continuous positive airway pressure (CPAP), which involves wearing a special mask that delivers steady air pressure through the nose during sleep.

The current study does not say anything about whether such treatments prevent or ease behavior issues.

Beebe said some research has found that kids who get their enlarged tonsils and adenoids removed show behavior improvements.

But those studies were not controlled clinical trials, in which kids would be randomly assigned to have the surgery or not. Those types of studies are considered the "gold standard" in showing that a treatment actually works.

"There is reason to believe that treatment might be helpful," Beebe said. "But we don't have the strong evidence we'd like."

There is, however, a clinical trial underway to test whether tonsil and adenoid surgery does help some kids' behavior problems.

The current study included 249 children who were followed from birth to age three. Overall, nine percent were considered persistent snorers, based on parents' reports. That meant they'd snored loudly at least twice a week at the ages of both two and three.

Another 23 percent were "transient" snorers, meaning they'd snored at least twice a week at either age two or three, but not both. The rest of the children, 68 percent, were considered non-snorers.

Overall, 35 percent of the persistent snorers scored high enough on a standard questionnaire to at least be considered "at risk" of a behavioral disorder. That doesn't mean they had one, though.

"It's not necessarily diagnostic," Beebe said. "But they're showing more problems than is typical."

There is a possibility that parents who complain of snoring problems are also more likely to complain about their kids' behavior, Beebe acknowledged.

But if that were the case in this study, he said, you'd probably see parents of transient snorers also report more behavior problems than parents of non-snorers did.

"But that's not what we see," Beebe said. "It's only if they're snoring at both ages."

There are reasons to believe that sleep-disordered breathing would affect children's behavior, according to Beebe. One reason is that poor sleep quality could make kids tired and more easily frustrated.

One study, Beebe noted, found that "nap-deprived" preschoolers had a tougher time with puzzles than their peers who got their nap.

And based on animal research, it's possible that when apnea causes oxygen levels to go down repeatedly overnight, there might be effects on the brain circuitry.

But there could also be other factors that explain the connection between snoring and behavior problems. Beebe's team accounted for family income, children's exposure to cigarette smoke and certain other factors, and the snoring-behavior link still held.

But, Beebe said, with these types of studies, it's always possible that there are other explanations.

For now, he recommended that parents be aware that persistent snoring is "not normal," and is something they should tell their pediatrician about.

SOURCE: bit.ly/jsoh2P Pediatrics, online August 13, 2012.

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