Snoring linked to chronic bronchitis

People who snore a few times a week are at a greater risk of developing chronic bronchitis, The Daily Telegraph reported today. GMTV added that a study has found that “those who snore six or seven times per week are 68% more likely to develop the condition than those who never snore”. Chronic bronchitis occurs when there is inflammation and obstruction of the air passages and symptoms include a cough that produces phlegm and shortness of breath. The Telegraph reported that “people who snore five times or less have a 25 per cent higher chance of developing bronchitis.”

The reports are based on a four-year study following 4,000 people in Korea, to see if they developed chronic bronchitis. However, this study cannot say that snoring causes the increase in risk, or whether some common factor increases the risk of both snoring and chronic bronchitis. There is no readily understood link between the two conditions, so using devices to stop snoring may or may not have an effect on the risk of chronic bronchitis. Smoking remains the strongest risk factor for developing chronic bronchitis and the findings of this study support this. Stopping smoking is the best strategy for people who want to reduce their risk of chronic bronchitis.

Where did the story come from?

Dr Inkyung Baik and colleagues from Korea University, Shiga University of Medical Science in Japan, and the University Of Virginia School Of Medicine in the US, carried out this research. The study was funded by the Korea Centres for Disease Control and Prevention, and the Japan Society for the Promotion of Science. It was published in the peer-reviewed medical journal: Archives of Internal Medicine .

What kind of scientific study was this?

This was a prospective cohort study looking at whether people who snored were more likely to develop bronchitis. The researchers enrolled 5,015 people aged 40 to 69 between June 2001 and January 2003, living in Ansan, a city near Seoul, Korea. The volunteers had a medical examination and were questioned about themselves, their health, lifestyle and their family disease history. The interview also included questions about whether they snored and how often (infrequently, once to three times a week, four to five times a week, or six to seven times a week). Those who reported that they coughed and produced phlegm on most days for three or more months of the year, or that they had been diagnosed with chronic obstructive pulmonary disease, cancer, tuberculosis, cardiovascular disease, or asthma, were excluded from the study. This left 4,270 people for analysis.

Researchers followed these participants for up to four years, and asked them to fill in questionnaires about their health every two years, to see if they developed chronic bronchitis. The researchers defined chronic bronchitis as coughing and production of phlegm on most days for three or more months of the year, for at least two successive years. Those who still met inclusion criteria after the first two years of the study were included in the second two years.

The researchers then looked at whether the proportion of people who developed chronic bronchitis differed between snorers and non-snorers. Snoring was classified as: never, five times a week or less, or almost every night (six to seven times a week). The researchers took into account factors that might affect risk of developing bronchitis, including age and smoking. They also looked at the joint effects of snoring and other risk factors for chronic bronchitis, including smoking, occupation, and body mass index (BMI).

What were the results of the study?

There were 314 new cases of chronic bronchitis during the four years of the study. People who snored six to seven nights a week were more likely to develop chronic bronchitis than people who did not snore. Although those who snored five times a week or less were at increased risk of chronic bronchitis, this increase did not reach statistical significance. People who smoked and snored were almost three times more likely to develop chronic bronchitis than people who did not smoke or snore.

What interpretations did the researchers draw from these results?

The researchers concluded that their results “support…the hypothesis that snoring influences the development of chronic bronchitis”. They suggest that more research is needed to confirm these findings and to understand exactly how it happens.

What does the NHS Knowledge Service make of this study?

This study has the advantages of being relatively large and collecting data prospectively over a period of time, and these factors increase the reliability of its results. However, there are some points to consider in interpreting the study, which the authors acknowledge:

• In this type of study, where researchers cannot randomly assign people to one group or another, there is always the problem that the groups differ in more ways than the one tested (in this case whether they snored), and that any differences seen in the outcomes (in this case chronic bronchitis) may be due to these imbalances. In this study, snorers were more likely to be male, older, have a higher body mass index, smoke, and drink more alcohol than non-snorers. Although the authors do try to account for these differences in their analyses, it may be that they, or other factors, are still having an effect.
• The researchers only asked participants whether they snored, and how frequently. It is not clear how accurate a person’s own report of their snoring is, and it may have improved accuracy to ask their sleeping partners, or to monitor them for snoring in their own homes. The authors acknowledge this, and aimed to counteract this by using the broad categories to classify snoring, so that misclassifications should have less effect on the results.
• In addition, chronic bronchitis was diagnosed only based on the participants’ reports, and was not confirmed by a doctor. This could lead to incorrect and missed diagnoses.
• This study was carried out in Korea, and the results may not apply to people living in different countries or with different ethnic backgrounds.

Smoking remains the strongest risk factor for developing chronic bronchitis and stopping is a far better strategy for people to reduce their risk of chronic bronchitis, than any changes that might affect snoring.

Sir Muir Gray adds...

If you want to avoid chronic bronchitis, don’t worry about the snoring, stay off the cigarettes.