A large South Korean study found frequent snoring was associated with the development of chronic bronchitis, but the researchers themselves said they aren't sure why.

"The mechanisms underlying the association between snoring and chronic bronchitis are largely unknown," said the report, published in the Jan. 28 issue of Archives of Internal Medicine, that was conducted by researchers at Korea University Ansan Hospital, in Ansan.

Bronchitis is inflammation of the air passages within the lungs. Acute bronchitis is often caused by an infection and goes away after treatment or on its own. Chronic bronchitis is most often caused by smoking or exposure to lung-irritating substances such as chemical fumes or dust, and does not go away quickly.

The Korean study of 4,270 individuals found that those who said they snored six to seven nights a week were 68 percent more likely to develop chronic bronchitis than those who said they never snored. The incidence of chronic bronchitis was 25 percent greater for people who snored five times a week or less.

Dr. Robert Keeton, a research fellow at the University of Michigan Sleep Disorders Center, called the findings an interesting association, "but you can't say it's conclusive. It can't be something you can cite to tell patients in the clinic that they have chronic bronchitis because they snore."

The Korean study proposed two possible reasons for the association. One is that the vibrations caused by snoring lead to inflammation in the airways. The other is that the inflammation comes first, causing the snoring and possibly sleep apnea, in which breathing stops or becomes very shallow periodically for 10 or 20 seconds.

"It's not unusual for people with obstructive sleep apnea to have such symptoms," Keeton said. "A common cause of snoring is obstructive sleep apnea."

Sleep apnea causes a distinctive kind of snoring, a loud gasping every time the airways are obstructed. Obese people are more likely to experience sleep apnea, but it can occur in persons of normal weight.

The incidence of sleep apnea is an unanswered question in the Korean study, said Dr. Charles Bae, a neurologist at the Cleveland Clinic Sleep Disorders Center. All the information in the study was based on reports by the participants, Bae noted, and there does not seem to have been an attempt by the researchers to determine how many of the patients may have had sleep apnea.

"There is certainly a relationship between sleep apnea and increased inflammation in the body," he said.

The bottom line, Bae said, is that the Korean paper "points out an interesting relationship that needs further research."