“Light” smoking — lighting up just a few cigarettes a day — can be almost as damaging to the lungs as heavy smoking, a new study has found.
A team of American researchers analyzed data from half a dozen previous studies involving thousands of current smokers, former smokers and people who had never smoked. Not surprisingly, they found that lung function — how much air a person can breathe in and out — declined faster among people who smoked than among those who had never smoked.
But they also found that the deterioration of lung function among “light” or occasional smokers (less than five cigarettes a day) was almost as fast as among heavy smokers (more than 30 cigarettes a day).
Lung function also continued to worsen for decades among the former smokers in the study, although not as quickly as among those who were still smoking.
The acceleration of lung function observed in the study helps to explain why smokers are at such high risk of developing chronic obstruction pulmonary disorder (COPD), a debilitating condition that makes it progressively more difficult to breathe.
“Many people assume that smoking a few cigarettes a day isn’t so bad,” says Dr. Elizabeth Oelsner, the study’s lead author and an assistant professor of medicine at Columbia University, in a released statement. “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.”
How the analysis was done
The researchers analyzed data from six U.S. studies involving more than 25,000 current, former and never smokers. The participants, who ranged in age from 17 to 93, were recruited into the studies between 1983 and 2014. They were given at least two lung-function tests (using a spirometer) at an average interval of seven years.
Using that data, the researchers calculated the rate of lung function decline among the participants. (Lung function weakens naturally with age, but it does so more quickly among people who smoke.)
After adjusting for confounding factors that can affect lung function, such as age, height, other lung diseases and exposure to secondhand smoke, the researchers found that the lung function of current smokers declined an average of 9.21 milliliters faster per year than that of never smokers.
The lung function of former smokers also declined faster than that of the people who never smoked, but at an average of 1.82 milliliters per year. The greater the number of years since people had given up smoking, the slower the decline.
Little difference was found between the light and the heavy smokers, however. Among light smokers, lung function declined 7.65 milliliters a year faster than among never-smokers. Among heavy smokers, it declined 11.24 millimeters per year faster.
Another way of looking at this, say the researchers, is that a light smoker lost the same amount of lung function in a year that a heavy smoker lost in nine months.
“Our results therefore reinforce the view that there is no safe level of tobacco smoke exposure and that smoking cessation is the most effective means of harm reduction,” Oelsner and her colleagues conclude.
Limitations and implications
The study comes with several caveats. The participants self-reported their smoking habits, and such reports are not always reliable. In addition, only 118 of the 2,462 participants who were current smokers said they smoked fewer than five cigarettes daily. Such a small number makes the lung function results of that group less trustworthy.
Still, the very serious risks that smoking poses to the lungs are well documented. What this new study adds is the finding that ex-smokers experience a decline in lung function that goes on for much longer than previously believed — up to 30 years, according to Oelsner.
“That’s consistent with a lot of biological studies,” Oelsner says. “There are anatomic differences in the lung that persist for years after smokers quit and gene activity also remains altered.”
The new study also suggests that light smokers are at much greater risk of developing COPD than once thought.
Both those findings underscore the need to avoid smoking — at any level.
“Smoking a few cigarettes a day is much riskier than a lot of people think,” Oelsner says. “Everyone should be strongly encouraged to quit smoking, no matter how many cigarettes per day they are using.”
FMI: The study was published in The Lancet Respiratory Medicine. You’ll find an abstract of the study on the journal’s website, but the full paper is behind a paywall. For help with quitting smoking, go to the American Lung Association’s website.