A new study by researchers at McGill University announced on July 22 could help explain why people who have quit smoking remain at elevated risk of lung disease long after their last cigarette.
The paper, published in Translational Research, provides a detailed picture of how quitting smoking affects the human lung at the cellular level. "Current smokers have the highest risk of deadly diseases such as lung cancer, but former smokers still face a higher risk than people who never smoked. Despite more than a century of research on smoking, we don't fully understand why," said Carolyn Baglole, Professor in McGill's Department of Pharmacology and Therapeutics and researcher at the Research Institute of the McGill University Health Centre.
"Our findings show that while some damage appears reversible, other changes persist long after people stop smoking," Baglole said. The research team analyzed more than 100,000 lung cells from 21 individuals—nine who had never smoked, five current smokers and seven former smokers—using publicly available data. This data captured molecular activity across over 40 different types of lung cells to offer a detailed view of how lungs respond to both active smoking and recovery after quitting.
Some lung cells recovered following cessation, while others showed persistent changes in genes linked to tissue structure, immune function, and blood vessel health. In certain cases, former smokers displayed molecular patterns not seen in either current or never-smokers. This suggests that quitting leaves its own biological signature on the lungs.
"These findings are an important step toward understanding what damage caused by smoking can heal and what may be permanent," said Nicole Heimbach, first author and doctoral student at McGill. "By knowing what damage remains after quitting, we can better understand how smoking-related diseases develop and how to treat them."
Although rates have declined over several decades, about one in eight Canadian adults still uses tobacco—a leading cause of preventable death.
