CHICAGO (AP) - New research suggests children who snore face nearly double the risk of being inattentive and hyperactive, providing fresh evidence of an intriguing link between sleep problems and attention deficit disorders.

While the study doesn't answer whether one condition causes the other, the researchers believe snoring and other sleep problems may be the culprit in some cases because children often express sleepiness by being inattentive and "hyper."

If it turns out to be true, this theory could help explain the paradox over why stimulants such as Ritalin can effectively treat children with conditions like attention deficit/hyperactivity disorder who already seem over-stimulated, said Dr. Ronald Chervin, a University of Michigan neurologist and sleep researcher, and the study's lead author.

"If there is indeed a cause-and-effect link, sleep problems in children could represent a major public health issue," Chervin said. "It's conceivable that by better identifying and treating children's snoring and other nighttime breathing problems, we could help address some of the most common and challenging childhood behavioral issues."

ADHD is the most common neurobehavioral disorder in childhood, affecting between 4 percent and 12 percent of school-age children - or as many as 3.8 million youngsters. Data cited by Chervin suggest that between 7 percent and 12 percent of children snore frequently, with apnea - brief breathing lapses during sleep that can cause snoring - present in up to 3 percent of school-age children.

Numerous other studies have found a link between sleep problems and ADHD, but many sleep specialists and psychiatrists are divided over which condition might cause the other.

"There's absolutely a connection," said Dr. Stephen Sheldon, a sleep specialist at Children's Memorial Hospital in Chicago. "There is a proportion of youngsters that have sleep pathology causing their daytime symptoms that appear virtually identical to ADHD."

Dr. Timothy Wilens, a child psychiatrist at Massachusetts General Hospital in Boston, is more skeptical.

"I would say the verdict is still out," said Wilens. ADHD is thought to have a genetic cause and runs in families, Wilens said. The sleep disturbances his research has found in ADHD children, including restlessness and difficulty falling asleep, are likely the result of behavioral problems, not vice versa, he said.

Chervin's study involving 866 children aged 2 through 13 is published in the March issue of Pediatrics. It is based on surveys of parents about their children's behavior and sleep patterns.

Parents rated their children's behavior based on a list of psychiatric criteria for ADHD, which includes impulsiveness, inability to pay attention and excessive activity. Parents weren't asked if their children had been diagnosed with ADHD, which Chervin acknowledged limits being able to generalize the results.

Overall, 16 percent were frequent snorers and 13 percent scored high on the ADHD scale.

Among frequent snorers, 22 percent had high ADHD scores, compared with only 12 percent among infrequent snorers.

Since snoring is often caused by apnea, which in turn is frequently caused by large tonsils, removing the tonsils might in some cases improve behavior, Chervin said.

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