Smokers who have passed a lung-function test may not be able to breathe easy for long, as a study published online June 22 in JAMA Internal Medicine has found that more than half of long-term smokers labeled “disease-free” in fact have some form of respiratory impairment.
“Many of those smokers likely have the early stages of chronic obstructive pulmonary disease," said Elizabeth Regan, MD, PhD, lead author and assistant professor of medicine at Denver’s National Jewish Health, in a statement. "We hope these findings will help debunk the myth of the healthy smoker and highlight the importance of smoking prevention and cessation to prevent lung disease and other long-term effects of smoking."
Among the conditions that can arise from long-term smoking is chronic obstructive pulmonary disease (COPD), which is the third leading cause of death in the U.S. It is diagnosed by having patients blow into a spirometer to measure the amount of air that can be forced out of the lungs.
Regan and colleagues wanted to look at a cohort of patients who did not meet the spirometric criteria for COPD and evaluate their results on chest CT scans, a six-minute walk exercise and questionnaires that assessed quality of life. Participants were recruited from 21 sites across the U.S.
The authors focused on a group of patients from the COPDGene study aged 45 to 80, who had all smoked at least 10 pack-years (a pack of cigarettes a day for 10 years), though the authors noted that most smoked significantly more, in the 35 to 50 pack-year range. Their results were compared to a smaller cohort of never smokers.
Of the 4,388 smokers who were considered disease-free based on their lung-function tests, 54.1 percent had one or more respiratory-related impairments. CT scans revealed emphysema or airway thickening in 42 percent of these seemingly healthy participants.
In addition to red flags on imaging, smokers fared significantly worse on the walking test, exhibited shortness of breath and had worse quality of life when compared with never smokers.
Regan and colleagues suggested that measures of forced expiratory volume on lung-function tests are useful at identifying obstruction when it is below population-defined limits of normal, but may not be effective at defining loss of function in cases where it has declined for an individual yet remains above population norms.
“Based on these results, we project that there are 35 million current and former smokers older than 55 years in the United States who may have unrecognized disease or impairment,” wrote the authors. “The effect of chronic smoking on the lungs and the individual is substantially underestimated when using spirometry alone.”