People with small airways relative to the size of their lungs may have an increased risk for COPD, regardless of whether they smoke, new research shows.

The retrospective observational study in JAMA of more than 6,500 older adults enrolled in three major lung studies in the United States and Canada found that individuals with smaller airways relative to lung size had the poorest lung function and were up to eight times more likely to develop COPD (defined by an  FEV1:FVC) of less than 0.70 with respiratory symptoms).

Airway to lung ratio statistically accounted for a greater proportion of variation in FEV1:FVC than smoking and other COPD risk factors.

According to the authors their findings may help explain why only some heavy smokers develop COPD and why up to 30% of COPD occurs among people who never smoked.

“Larger than predicted airway tree size may signal physiological reserve to sustain noxious particulate-pollutant–induced or asthma-induced airway narrowing (and associated reduction in airflow) without reaching the FEV1:FVC threshold that defines COPD…conversely, people with smaller than predicted airway tree size who never smoked may require no additional risk factor to meet the spirometric criteria for COPD,” they wrote in their paper published in JAMA.

“Our findings suggest that dysanapsis is a major COPD risk factor — on par with cigarette smoking,” concluded lead author Benjamin M. Smith, MD, assistant professor of medicine at Columbia University Vagelos College of Physicians and Surgeons.

“Dysanapsis is believed to arise early in life. Understanding the biological basis of dysanapsis may one day lead to early life interventions to promote healthy and resilient lung development,” he added.