Snoring in children may be a manifestation of allergic disease, Australian researchers report.

In a group of 5-year-olds participating in an asthma prevention study, Dr. Nathaniel S. Marshall of the Woolcock Institute for Medical Research in Sydney and his associates found that risk factors for snoring were very similar to those for allergic disorders. These risk factors included exposure to cigarette smoke in the first year of life, asthma and eczema.

In adults, snoring is strongly tied to obesity. But in children, the swelling of the lining of their smaller airways may be a stronger risk factor, Marshall and his team suggest in the current issue of Pediatric Pulmonology.

To better understand risk factors for snoring in children and the relationship between snoring and allergic disease, the researchers looked at a subgroup of 213 participants in an asthma prevention study. The parents reported that their children had rhinitis -- an itchy, stuffy or blocked nose -- for at least a week in the previous year. Nearly 60 percent of these children snored at least once a week. Just over one quarter snored more than three nights a week.

First-born children were 2.5 times more likely to snore than children with older siblings. A number of studies have found oldest children are at greater risk of allergic diseases, the researchers note.

Having a mother who smoked in the home during a child's first year of life boosted snoring risk 2.4-fold. Children with asthma were 2.51 times more likely to be snorers, while having eczema increased the likelihood of snoring 2.29-fold.

However, children's body mass index had no relationship to whether or not they snored.

"Although the association between obesity and snoring has been well established in adults and school-age children, our findings imply that body mass is not an important contributor to snoring in pre-school age children," Marshall and his team write. "It seems likely that upper airway morphology (shape) and the manifestations of allergic disease are more important."

They conclude: "Snoring in children may be regarded as part of the spectrum of allergic diseases."