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And yet, in cells from ex-smokers, the airway epithelium also showed large clusters of healthy cells without smoking-related genetic damage. These cells were just as healthy as those from non-smokers and indicated a low risk of lung cancer. And once the person quit, they were beginning to repair the airway lining that had been damaged by smoking.
Unexpectedly, there were four times as many of these healthy cells in ex-smokers than in current smokers. In fact, these cells made up about 40% of all lung cells in smokers who had quit.
The current research shows the useful outcomes of stopping cigarette smoking. For one, it prevents further lung damage. However, it goes beyond that. It allows the airway lining to be renewed by the active proliferation of new healthy cells. Thus, the balance between sick or damaged cells and healthy cells shifts in favor of the latter, leading to a net protective effect that could help prevent lung cancer. This strongly supports the benefits of quitting smoking, whatever the smoker’s age, to allow these beneficial effects to take place. Public health implications
Researcher Peter Campbell explains: “People who have smoked heavily for 30, 40 or more years often say to me that it's too late to stop smoking - the damage is already done. What is so exciting about our study is that it shows that it's never too late to quit - some of the people in our study had smoked more than 15,000 packs of cigarettes over their life, but within a few years of quitting many of the cells lining their airways showed no evidence of damage from tobacco.”
On the other hand, there are other features of smoking-induced damage that impair the elastic recoil of the lung tissue. The normal elastic nature of lung tissue helps to push out air with each exhalation, and damage to the elastic tissue can cause chronic obstructive lung disease such as emphysema. This cannot be reversed even after quitting, unlike the genetic changes.
Overall, the researchers say it is worth stopping smoking to reduce lung cancer risk, whatever the age. Quitting both prevents further damage to the lung cell genome, and stimulates undamaged cells to replace the mutated ones, protecting the lungs against cancer. Cancer Research UK’s Rachel Orritt explains, “It's a really motivating idea that people who stop smoking might reap the benefits twice over - by preventing more tobacco-related damage to lung cells, and by giving their lungs the chance to balance out some of the existing damage with healthier cells. What's needed now are larger studies that look at cell changes in the same people over time to confirm these findings.
"The results add to existing evidence that, if you smoke, stopping completely is the best thing you can do for your health. It's not always easy to kick the habit, but getting support from a free, local Stop Smoking Service roughly triples the chance of success compared to going it alone." Journal reference:
Yoshida, K., Gowers, K.H.C., Lee-Six, H. et al. Tobacco smoking and somatic mutations in human bronchial epithelium. Nature (2020). https://doi.org/10.1038/s41586-020-1961-1
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