New United States research has found that quitting smoking can improve lung health, even in those were previously heavy smokers, but cutting down is not enough to preserve lung function.
Carried out by researchers at various universities across the United States, the study gathered data from 3,140 participants who were taking part in the Coronary Artery Risk Development in Young Adults (CARDIA) study.
The participants had an average age of 25 when they enrolled in the study, and data was collected over a 30-year period, with participants completing spirometry tests to assess lung function and chest CT scans 15, 20 and 25 years after enrolling.
“The CARDIA dataset gave us a unique opportunity to learn about the impact of different levels of smoking on lung health and lung disease risk,” said lead author Amanda Mathew at Northwestern University Feinberg School of Medicine. “Participants were asked about their smoking each year, which minimized recall bias and allowed us to model changes in smoking habits over time.”
The team found that compared to those who never smoked, those in the group who had been consistent heavy smokers experienced the greatest decline in lung function.
In addition, this group were also 26 times more likely to develop emphysema and nearly eight times more likely to develop obstructive lung disease.
The researchers also looked at light smokers, a group who they say are rarely included in clinical trials and so less is known about their lung health outcomes. Light smokers were defined as having a less than a 10 pack-years smoking history, with pack-years calculated by multiplying the number of cigarette packs smoked a day times the number of years a person smoked.
The team then compared the consistent light smokers (who had a 6.4 pack-year history) with smokers who had quit (who had a 9.8 pack-year history).
They found that despite having smoked more cigarettes during their life, the heavier smokers who had quit preserved more lung function and had a lower risk of developing emphysema than the light smokers.
“We were surprised to find that those who quit had lower disease risk than the group we identified as stable, low-rate smokers, even though those who quit had a greater lifetime exposure to cigarettes,” said Dr. Mathew. “There is no safe threshold of smoking on lung health. Cutting down can be a great first step, but quitting for good is the most effective way to reduce lung disease risk.”
The findings can be found published online in the American Journal of Respiratory and Critical Care Medicine. JB