Snoring may significantly increase susceptibility to chronic bronchitis, investigators here have found.

Regular snoring was associated with a 25% to 68% increased frequency of new-onset chronic bronchitis compared with those who never snored, Chol Shin, M.D., Ph.D., of Korea University Ansan Hospital, and colleagues reported today in the Archives of Internal Medicine.

The combination of smoking and snoring almost tripled the likelihood of chronic bronchitis compared with those who did not smoke or snore.

"Our findings may provide novel information that snorers are at greater risk of developing chronic bronchitis than persons who do not snore during sleep," the authors concluded.

The findings are consistent with previous studies showing that patients with chronic bronchitis are more likely to snore and that nonsmokers with chronic bronchitis are twice as likely to snore regularly compared with nonsmokers without chronic bronchitis, the authors said. However, a causal relationship between chronic bronchitis and snoring has not been demonstrated, and mechanistic explanations remain largely nonexistent.

Continuing the exploration of associations between snoring and chronic bronchitis, Dr. Shin and colleagues examined data on 4,270 Korean adults who participated in a prospective health examination. The participants enrolled from June 25, 2001 to Jan. 29, 2003 and were followed through Nov. 17, 2006. Information on snoring was collected at enrollment.

During follow-up, investigators documented 314 cases of new-onset chronic bronchitis (27.1 cases per 1,000 person-years). In a multivariate analysis that controlled for age, smoking, and other risk factors for chronic bronchitis, snoring five or fewer times weekly increased the risk of chronic bronchitis by 25% compared with never-snorers (RR 1.25, 95% CI 0.95 to 1.64). More frequent snoring bumped the relative risk to 1.68 (95% CI 1.17 to 2.42).

Stratification by chronic bronchitis risk factors that included smoking, occupation, and body mass index showed stronger associations among never-smokers, house workers, and overweight people.

An examination of the joint effect of snoring and smoking on chronic bronchitis revealed a relative risk versus nonsmoking-never-snorer of:

* 1.39 for nonsmoking and snoring (95% CI 1.01 to 1.90)
* 2.31 for smoking and never-snoring (95% CI 1.38 to 3.87)
* 2.86 for smoking and snoring (95% CI 1.91 to 4.27)

The authors acknowledged that information on chronic bronchitis was self-reported, not documented by medical records, and the information on snoring was not verified. They also acknowledged that they could not rule out potential confounding effects of unknown and uncontrolled factors.