Growing up in the eighties I was surrounded by smoke. Nearly every adult in my extended family was a cigarette smoker, and I can personally speak to the horror of drinking from a Coke can that had been used as an ashtray. As I got older, I didn't see the appeal of trying it myself. In retrospect, I don't remember how influenced I was by anti-smoking campaigns of the time. I just think I was overwhelmed by cigarette smoke and didn't need another means to get it into my body.
My mother quit smoking when I was in my late 20's. She got the flu during the Christmas holiday, and decided to not smoke again after a week of being unable to do so. It didn't hurt that the price of a carton of cigarettes had recently skyrocketed, and smoking was no longer a casual habit, but a real investment.
This extended preamble is my way of explaining that when I listen recent journal club for this paper from Kyungyon, et al in Nature, I felt more than scientific curiosity .... I felt personally invested.
It's no surprise to most people that lung cancers occur more frequently in smokers. Or, if it is a shock to you, here are some facts to really drive home that point:
* Lung cancer is the 6th most common cause of death world-wide
(heart attack and stroke are 1 and 2)
* It is the 2nd most frequently diagnosed cancer
(behind breast cancer in women and prostate cancer in men)
* 90% of lung cancers are due to smoking
90% !!
Although I assumed that smoking was the leading cause of lung cancer, I had no idea that it was very nearly the sole cause of lung cancer.
So now then, what is the motivation to keep reading. According to the above points, you'd think smoking is signing your own death certificate. That once you start, it is all a lost cause.
90%....those are pretty crazy odds.
But here's the thing that is really fascinating to me. The body is an amazing machine, and it wants to survive. As clear as the correlation between smoking and lung cancer is, so too is the ability of the cells of the lungs to beat these odds.
A 2013 New England Journal of Medicine study found that life expectancy goes up after quitting smoking. Individuals that quit add an additional 4-10 years to their lives . The younger you are when you quit, the higher the number of years is. That same study found that quitting smoking before age 40 reduces your chance of a smoking related death by 90%. And as we learned already, 90% is a pretty impressive amount.
This leads me to this recent study in Nature:
Tobacco smoking and somatic mutations in human bronchial epithelium.
The authors collected lung tissue samples from 16 individuals from 4 different groups:
3 children
4 never smokers
6 ex-smokers
3 current smokers
All of these individuals were scheduled to receive bronchioscopies (a procedure in which the doctor uses a special light and camera that are inserted through a thin tube into the patient's lung). Because they were already receiving bronchioscopies, these individuals may not completely represent the total population of individuals in their category. They may have had some pre-existing conditions independent of smoking status, which lead them to needing a bronchioscopy, and this may have influenced the data. But, as any scientist that deals with patient samples will tell you, there is always patient to patient variability.
We are all unique snowflakes! Sorry to break it to the people that use that as an insult, but indeed regardless of our political leanings, we are all special unique beings and not genetically identical lab animals. Actually, this report also found that individual cells within a single patient had a lot of variability. So maybe we are actually snowflakes filled with snowflakes?
The authors point out that bronchial tissue collected was normal for all of these individuals, regardless of smoking status. The researchers used these samples to analyze the genetic mutations in single cells. It is genetic mutations that change a normal healthy cell into a cancer cell.
The bad news (for all of us humans) is that aging increases the frequency of mutations. This should also not be a complete shock. Living in the modern world means we breathe, and we breathe in some things that irritate our lung tissue and may cause mutations in the cells in that tissue. If anything it is a testament to the fact that we aren't all dying in childhood of infectious diseases or minor injuries; that we have time to live and gradually get some mutations. But having mutations in our genes doesn't necessarily cause cancer. Again our bodies are amazing machines, and can tolerate or correct certain mutations.
As expected, cells from smokers' lungs had a greater number of mutations than never smoker adults and children. But, ex-smokers had less mutations than current smokers.
The surprise in this analysis was when they looked at cells that were fairly normal. Smokers had very few cells that were normal, but ex-smokers had 4x more normal cells than current smokers. What this implies is huge. While a person is smoking, they have this higher mutational burden in their lung cells, however when they quit, the small number of normal cells remaining have the chance to thrive and renew. This allows healthy tissue to begin to rebuild in the lungs of individuals that have quit smoking.
This fancy analysis supports the evidence that quitting smoking increases the lives of ex-smokers. It shows a direct mechanism. Even though smoking induces potentially cancerous mutations in the lung cells of smokers, the cells that are normal can rebuild the environment when smoking is stopped.
Okay, as I mentioned in the introduction, I've spent my life surrounded by smokers, and as such I've also been surrounded by attempts at going cold turkey, using patches, and chewing gum. Quitting smoking is not a easy. Although I am no longer surrounded by smokers, most of those ex-smokers in my life took several attempts to quit. This is probably why I still have nightmares that my mother has started smoking again. However, I think these findings demonstrate that the effort is worth it. As soon as you stop smoking, your body starts the process of rebuilding from the damage. It is important to note, that ex-smokers are still at higher risk than never smokers, but the risk of developing lung cancer drops by 40% within 5 years after smoking is stopped.
My hope is that smoking becomes even less common and these lung cancer statistics continue to decline. I do worry that the effects of electronic cigarettes and vaping may also contribute heavily to these data in the future. However, it is still relatively early days for epidemiological studies to include the long term effects of these alternate methods.
Smoking is no longer permitted in most public buildings. Gone are the days of the smoking section in restaurants (which never really blocked smoke from the non-smoking sections). I don't miss a night out for drinks that ended smelling like stale cigarettes the next morning, or standing watching a band and getting a cigarette burn on my arm. I think the only thing I miss about the smoking culture of my youth is the big ornamental ashtrays that decorated living rooms in the 70's and 80's. Though I think I can manage to deal with that loss, if it means a extra years added to the lives of people that I care about.
Sources:
de Groot et al, The epidemiology of lung cancer, Translational Lung Cancer Research, 2018, 7(3):220–233
Jha et al, 21st-Century Hazards of Smoking and Benefits of Cessation in the United States, New England Journal of Medicine, 2013, 368:341-350
Tindle et al, Lifetime Smoking History and Risk of Lung Cancer: Results From the Framingham Heart Study, 2018, Journal of the National Cancer Institute, 110: 1201–1207
World Health Organization: The top 10 causes of death
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