Any Level of Smoking Can Lead to Long-term Lung Damage, Study Says

Former smokers and people who smoke relatively few cigarettes per day may experience a faster decline in lung function than people who have never smoked, although they still have a slower decline in lung function than current smokers, a new study suggests.

The study, “Lung function decline in former smokers and low-intensity current smokers: a secondary data analysis of the NHLBI Pooled Cohorts Study,” was published in The Lancet Respiratory Medicine.

Smoking is well-established as being detrimental to lung health. In fact, smoking is known to cause the development of chronic obstructive pulmonary disease (COPD). And light smokers are not exempt from causing damage to their lungs, according to the researchers.

“Many people assume that smoking a few cigarettes a day isn’t so bad,” Elizabeth Oelsner, MD, study co-author and a professor at Columbia University Vagelos College of Physicians and Surgeons, said in a 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,” she said.

In the study, Oelsner and her colleagues analyzed data from the NHLBI Pooled Cohorts Study, which included data from 25,352 people (17–93 years old) who had multiple assessments of lung function, as measured via forced expiratory volume (FEV), the amount of air a person can exhale.

With a median follow-up time of seven years, and at a median age of 57, people who had never smoked experienced a FEV decrease at an average rate of 31.01 mL per year. This was expected, as FEV is known to decrease throughout life starting when people are in their 20s.

In former smokers, the rate of FEV decline was higher at 34.97 mL per year, while in current smokers, it was 39.92 mL per year. This suggests that smoking results in a rapid decline in lung function long after a person has quit.

“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.”

Using statistical analyses, the researchers calculated effect estimates (how much an activity, in this case smoking, is predicted to have an impact on a measurement, in this case FEV) for current smokers who smoked many or a few cigarettes per day. Among current smokers who smoked 30 or more cigarettes per day, the effect estimate was the loss of 11.24 mL per year, while for those who smoked less than five cigarettes per day, it was a loss of 7.65 mL per year.

“Former smokers and low-intensity current smokers have accelerated lung function decline compared with never-smokers. These results suggest that all levels of smoking exposure are likely to be associated with lasting and progressive lung damage,” the researchers wrote.

The data also suggested that light smokers may be at a higher risk of COPD than previously thought. Of note, COPD is diagnosed when FEV decreases below a certain point, and most studies assessing the link between COPD and smoking focused on smokers with heavier habits.

“We probably need to expand our notions of who is at risk,” Oelsner said. “In the future, if we find therapies that reduce the risk of developing COPD, everyone at increased risk should benefit.”

Overall, the results re-emphasize that smoking causes real, long-term damage to the lungs, and so smoking (at all levels) should be avoided, the researchers said.

“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.”