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A new study shows that smoking just a few cigarettes a day is harmful to lungs and that former smokers continue to lose lung function at a faster rate than never-smokers, decades after quitting.

People who smoke fewer than five cigarettes a day cause long-term damage to their lungs, according to a new study led by researchers at Columbia University Vagelos College of Physicians and Surgeons.

“Many people assume that smoking a few cigarettes a day isn’t so bad,”

“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.”

– Study leader Elizabeth Oelsner, MD, a Herbert Irving Assistant Professor of Medicine at Columbia University Vagelos College of Physicians and Surgeons.

The research team at Columbia University specifically looked at lung function and the amount of air a person can breathe in and out – in smokers, ex-smokers, and never-smokers. Lung function naturally declines with age and it’s well-known that smoking accelerates the decline.

The study is large, with more than 25,000 participants. The team could see clear differences in lung function among light smokers (<5 cigarettes/day) and heavy smokers (>30) that other studies have been unable to detect.

Their analysis found that lung function in light smokers declines at a rate much closer to that of heavy smokers than non-smokers. Their results show that light smokers could lose about the same amount of lung function in one year as a heavy smoker might lose in nine months.

The study also tested a long-held assumption, based on a 40-year-old study, that the rate of decline in lung capacity “normalizes” within a few years of quitting. Contrary to that study, however, the new study shows that although lung capacity declines at a much lower rate in ex-smokers (an extra 1.57 mL/year compared with nonsmokers) than current smokers (an extra 9.42 mL/year), the rate doesn’t normalize (reach zero) for at least 30 years.

Smoking is one of the leading causes of preventable death globally. In the United States, about 500,000 deaths per year are attributed to smoking-related diseases and a recent study estimated that as much as 1/3 of China’s male population will have significantly shortened life-spans due to smoking. Cigarettes are smoked by over 1 billion people, which is about 20% of the world’s population. About 800 million of these smokers are men.


Elizabeth C Oelsner et al. Lung function decline in former smokers and low-intensity current smokers: a secondary data analysis of the NHLBI Pooled Cohorts Study DOI:https://www.thelancet.com/journals/lanres/article/PIIS2213-2600(19)30276-0/fulltext