FRIDAY, Oct. 11, 2019 (HealthDay News) -- Even light smoking causes long-term damage to lungs, researchers warn.
In a new study, they compared lung function -- how much air a person can breathe in and out -- from more than 25,000 people. The analysis included nonsmokers, light smokers (fewer than five cigarettes a day) and heavy smokers (more than 30 cigarettes a day).
The light smokers' lung function declined at a rate more similar to heavy smokers than to nonsmokers. Compared to people who had never smoked, lung function decline was 7.65 mL/year greater among light smokers and 11.24 mL/year greater among heavy smokers.
The upshot: A light smoker could lose roughly the same amount of lung function in one year as a heavy smoker might lose in nine months, according to the Columbia University-led study.
"Many people assume that smoking a few cigarettes a day isn't so bad," study leader Dr. Elizabeth Oelsner said in a university news release. "But it turns out that the difference in loss of lung function between someone who smokes five cigarettes a day versus two packs a day is relatively small."
Oelsner is an assistant professor of medicine at Columbia's Vagelos College of Physicians and Surgeons in New York City.
Starting in the 20s, lung function declines naturally with age, and smoking speeds the decline.
"Smoking a few cigarettes a day is much riskier than a lot of people think," Oelsner said. "Everyone should be strongly encouraged to quit smoking, no matter how many cigarettes per day they are using."
When a smoker quits, the decline in lung capacity slows, but the rate of decline doesn't return to normal for at least 30 years, the study showed.
"That's consistent with a lot of biological studies," Oelsner said. "There are anatomic differences in the lung that persist for years after smokers quit and gene activity also remains altered."
The accelerated lung function decline explains why smokers are more likely to develop chronic obstructive pulmonary disease (COPD). It's diagnosed when lung function falls below a set level.
Light smokers may have a greater risk of developing COPD than most researchers have thought, according to Oelsner, who noted most COPD studies have focused on heavy smokers.
"We probably need to expand our notions of who is at risk," she said. "In the future, if we find therapies that reduce the risk of developing COPD, everyone at increased risk should benefit."
The study was published online Oct. 9 in The Lancet Respiratory Medicine.
The U.S. National Heart, Lung, and Blood Institute has more on COPD.