Health & Wellness

Why Some Non-Smokers Get COPD While Many Smokers Don’t

Small airways in the lungs may help explain pulmonary disease in non-smokers

The best-known risk factor for chronic obstructive pulmonary disease (COPD) is smoking. Despite that, more than 25% of all cases of the disease are seen in lifetime non-smokers. A new study from the McGill University Health Centre published in the Journal of the American Medical Association suggests that may be because a condition called dysanapsis is another significant risk factor for COPD.

COPD is the fourth leading cause of death in Canada and is associated with obstructed airways, chronic coughing, and shortness of breath that interferes with day-to-day activities. According to the Canadian Centre for Health and Safety, 4% of Canadians are diagnosed with the illness.

Dysanapsis involves a mismatch between airways and lung size, which occurs when airways in the lungs don’t grow to match the size of the lungs over time.

“When people breathe, they move air through their airways, beginning with the windpipe or trachea, which branches out to smaller airways called bronchi and bronchioles,” explains Dr. Benjamin Smith, the lead author of the study and an associate professor in the McGill University’s Department of Medicine. “As people grow, their airways are thought to develop in proportion to their lungs, but in some people, the airways do not get as large as expected.”

Looking over data for 6,500 COPD patients involved in three separate studies in Canada and the United States, researchers found that lifetime non-smokers with COPD tended to have smaller airways in comparison to smokers who had never had COPD but “unusually” large airways.

“With normal aging, lung function declines,” Smith said. “Because of that decline, people with smaller airways—who already have low lung function to begin with—may develop COPD later in life. On the other hand, smokers with larger airways might have some reserve to withstand the harmful effects of smoking.”

Nevertheless, Smith emphasized that quitting smoking remains “of paramount importance.” Researchers also found that smoking led to a faster decline in lung function among COPD patients than dysanapsis did.




Photo: iStock/magicmine.