"Lungs 'magically' heal damage from smoking," reports BBC News. This encouraging headline is prompted by a new UK-based study.
Researchers examined lung cells from children, adults who had never smoked, smokers and ex-smokers to look for DNA mutations. As expected, they found thousands of mutations in cells of smokers and ex-smokers, including mutations known to lead to cancer. However, they also found a surprising amount of variation within the samples of cells from ex-smokers.
Even in people who had smoked heavily for decades before quitting, some of their cells were near-normal. This suggests the cells had grown since people had stopped smoking. These normal cells were not found in current smokers.
Although the study is very small, this finding is encouraging. It suggests people who stop smoking can reduce their risk of cancer, not just by avoiding more damage, but because some of the cancer-causing cells are replaced over time.
This shows it is never too late to reduce or begin to reverse the damage caused by smoking – although the sooner you stop, the better your chances of avoiding diseases such as cancer. Stopping smoking can also help you feel less stressed, breathe more easily and have better skin and whiter teeth.
Find out about the health benefits you could see if you stopped smoking today.
Where did the story come from?
The researchers who carried out the study were from the Wellcome Trust Sanger Institute, University College London and Kyoto University in Japan. It was funded by Cancer Research UK and the Wellcome Trust. It was published in the peer-reviewed science journal Nature.
Most of the headlines in the UK media reports used the word "magic" to describe the growth of healthy cells after people stopped smoking. This is because scientists do not yet understand how it happens. The problem with suggesting lung regeneration happens by magic is that it might make people feel they do not have to worry about damage from smoking, so long as they stop at some point. Apart from this, the reports mostly do a good job of explaining what the study found.
What kind of research was this?
This was an experimental study using genetic sequencing of samples of lung cells taken from 16 people. Genetic sequencing is a technique that allows researchers to study the individual molecules of DNA that make up cells.
Experimental studies tend to be small, which means their results are less reliable than bigger studies. But they help scientists understand how the body works, which can help them give good health advice and design better treatments in future.
What did the research involve?
Researchers took samples of cells from the lining of the airways inside the lungs, from 16 people having bronchoscopies. The bronchoscopy test involves putting a thin tube into the lungs, which has a small chance of causing damage. Because of this, the researchers could only sample people who were having a bronchoscopy for medical investigations, who agreed that their samples could also be used for this study.
The 16 people included 3 children, 4 people who had never smoked, 6 ex-smokers and 3 current smokers. Each person's individual cells were grown separately to form colonies big enough to carry out whole genome sequencing. This gave the scientists DNA results from 632 individual cells taken from people's lungs.
Researchers looked at:
- the average number of DNA mutations in each cell
- the proportion of cells that had mutations known to lead to cancer
- the length of telomeres (the "caps" to DNA strands that protect them from damage) and how that was related to DNA mutations
They then calculated how the results varied according to people's age and smoking history.
What were the basic results?
The researchers found that age and smoking history increased the number of mutations in people's cells:
- people's cells picked up an average 22 mutations each year
- ex-smokers had around 2,330 more mutations per cell than non-smokers
- current smokers had around 5,300 more mutations per cell than non-smokers
However, they also found a lot of variation between cells from the same people, if they were ex-smokers. Around 20% to 40% of cells from ex-smokers had the same level of mutations as you would expect in someone the same age who had not smoked. These "normal" cells were rare in cells from current smokers.
Mutations known to lead to cancer were found in:
- no cells from children
- 4% to 14% of cells from adults who had not smoked
- 25% or more of cells from adults who currently smoked
Cancer-related mutation cells were twice as common in current smokers as in those who had never smoked.
The researchers found that telomere length was not related to the number of mutations in cells from children or adult non-smokers. However, the more mutations in a smoker's lung cells, the shorter their telomere lengths. This could mean that these cells would be more vulnerable to damage.
How did the researchers interpret the results?
The researchers said their results were "unexpected" and that they had found cells "clearly protective against lung cancer" in the lungs of ex-smokers. They speculate that these cells may be "recent descendants of quiescent [dormant, or sleeping] stem cells", which escaped damage from tobacco by being inactive until smoking stopped.
They add: "The message to public health is that stopping smoking – at any age – does not just slow the accumulation of further damage, but can also reawaken cells that have not been damaged by past lifestyle choices."
This is a good news story. Many people who have smoked for a long time believe that there is no point in stopping, because the damage has been done. This study suggests that stopping smoking not only prevents further damage to cells, but could allow the lungs to start to repair themselves by growing new cells.
The study is small, and the people who gave samples were not randomly selected because they were being investigated for medical conditions. That means we cannot be sure, for example, that the levels of mutations in people's cells are average for people in general. It would be useful to see these results reproduced using a bigger and more representative group of people.
However, the findings that some cells from the 6 ex-smokers in the study were near-normal, while others had thousands of mutations, should not be affected by the size of the study.
The results add strength to the message that the best thing you can do for your health, if you smoke tobacco, is to stop smoking.
You can get help and find out about treatments that make it easier to stop.
Analysis by Bazian
Edited by NHS Website
Links to the headlines
BBC News, 29 January 2020
The Guardian, 30 January 2020
The Independent, 30 January 2020
The Sun, 29 January 2020
Mail Online, 30 January 2020
Links to the science
Nature. Published online 29 January 2020