Just statements like 'smoking causes cancer' or 'smoking doesn't cause cancer' don't explain the complex situations in a human body.

Smoking and health issues

Q: I think scientists say very alarmistic things. 

If cigarette smoking can lead to cancer, then how come so many people still survive despite smoking for 2 to 3 decades? 

Q: Scientists say eating processed food is bad. They say "this thing" is bad for health and "that thing" causes cancer. My grandparents have been eating and drinking all those things since ages. They didn't have any health problems. Why should we believe them, when scientists say these things are bad for health?

Krishna: :) I get these types of questions several times. I explained it several times too. Okay, let me do it one more time.  

Things are not that easy and simple to say this causes that, that causes this and this is really responsible for that and this. They are very, very complicated. 

There are a number of reasons why smoking does cause cancer: among these, DNA damage is a primary factor. We do also know that most lung cancers are caused by smoking, and smoking is also responsible for most lung cancer-related deaths. But not all smokers develop lung cancer — and scientists have now found that a genetic dice roll may be a factor.

Researchers found that some smokers who have never developed lung cancer have a lining of surface cells in their lungs that are less likely to mutate over time — moreover, they also may have stronger DNA repairing genes. Surface cells are the ones most likely to turn cancerous; “[t]hese lung cells survive for years, even decades, and thus can accumulate mutations with both age and smoking (1)

They found that the mutation risk steadily rises over time as the frequency of smoking increases. However, after 23 pack–years, the risk of cell mutation plateaus in some people(1).

Data suggest that these individuals may have survived for so long in spite of their heavy smoking because they managed to suppress further mutation accumulation. This leveling off of mutations could stem from these people having very proficient systems for repairing DNA damage or detoxifying cigarette smoke,” the researchers explain in their paper(1).

The research is meant to highlight genetic factors that could play a role in mitigating that risk for some.

The other side of the coin is that there are also genetic flaws that make some people more susceptible to becoming addicted to and developing lung cancer from smoking than others. This research was published in Nature way back in 2008 (4), and showed how a particular gene makes some people more likely to develop lung cancer than others.

The problem with smoking isn’t that it causes many of the problems most often associated with it (most notably cancer) directly, but that it exacerbates them in likely sufferers.

It’s likely that people’s predisposition to those conditions is genetic, in their DNA. Some people have no genetic predisposition to getting cancer for example. Any of those people might smoke and smoke for many years with few ill effects at all.

Having a predisposition doesn’t mean anyone will definitely contract cancer. However…

If a person with a genetic predisposition to contracting cancer is a smoker, the likelihood of them contracting it is much higher.

Now, smoking is associated with many more health problems than just cancer - think emphysema, heart disease and many others. If a person has a genetic predisposition toward contracting any of these conditions, as a smoker their likelihood of contracting them is much higher.

Moreover, human biochemistry is highly complex.

 Even if a genetically predisposed person smokes cigarettes, he might also be taking certain steps like eating very healthy foods, food that can eradicate all the ill effects of smoking. 

The key is in the DNA’s ability to repair and resist environmental toxins such as cigarette smoke. Previous research has also found that B-vitamins — particularly B6 — are important in maintaining DNA health. “Basically, these B vitamins and nutrients are all involved in the pathway which is responsible for the creation and maintenance of DNA (2).

Then the immune system can change the gut microbiota. Microbiota may induce carcinogenesis by several mechanisms. It also affects tumour progression. Thus, microbiota modulation may aid in the prevention and treatment of cancer. Meaning the good microbiota and the chemicals they produce balance out the wrong mechanisms caused by cigarette smoking  or eating unhealthy food.

Then physical activity, from low to moderate to high, was significantly associated with more years of life expectancy in both smokers and non smokers (5).

Other studies (3) have  shown that some DNA mutations enhance lung function and keep you away from certain ill effects of smoking.

Analysis suggests people with more copies of ribosomal DNA have higher risks of developing disease. Ribosomal DNA (rDNA) is present in hundreds of copies in the genome, but has not previously been part of genetic analyses. A new study of 500,000 individuals indicates that people who have more copies of rDNA are more likely to develop inflammation and diseases during their lifetimes. Standard genetic analysis techniques have not studied areas of the human genome that are repetitive, such as ribosomal DNA (rDNA), a fundamental part of the molecular mechanism which makes proteins in cells. A new study has discovered that genetic disposition to disease can be found in these previously understudied areas of the genome. The results, published in Cell Genomics recently, suggest that wider genome analysis could bring opportunities for preventative diagnostics, novel therapeutics, and greater insight into the mechanism of different human diseases (7).

You really don't know what version of the gene you have and decide whether to keep on smoking or not… You have to bear in mind that there are so many other disease[s] that are caused by smoking, apart from cancer.

So it is better to be cautious. That is why scientists bring these things to your notice. This is  an important step toward the prevention and early detection of  cancer risk.

 Smoking can damage all parts of your body, down to your DNA. But it’s very hard to quit because of its effects on your brain. Image source: Cleveland Clinic

Sometimes you get the results after several years of taking something bad. By the time you face the consequences, you would have almost forgotten the bad things you did long, long back. So you can't even guess  that the ball you threw ages ago came back and hit you in the wrong place and with a deadly result. 

Evidence shows that smokers die earlier than non-smokers.

The scientific consensus remains clear on the fact that smoking is deadly on several fronts. 

When several factors decide outcomes, they follow the interplay of scientific rules and routes and exactly fit into the reaction realities. You have to register this in your mind to really understand the mechanisms. How a person escapes or survives a health condition or a catastrophe or a bad situation depends on the sum total outcomes of scientific factors occurring simultaneously (6).

 Just statements like 'smoking causes cancer' or 'smoking doesn't cause cancer' don't explain the complex situations in a human body.

Footnotes:

1. https://www.nature.com/articles/s41588-022-01035-w#Sec2
2. https://www.reuters.com/article/us-cancer-lung-nutrients-sb-idUSTRE...
3. https://www.independent.co.uk/life-style/health-and-families/health...
4. https://www.scientificamerican.com/article/why-some-smokers-get-lung/
5. https://pubmed.ncbi.nlm.nih.gov/10192312/#:~:text=Physical%20activi...).
6. https://kkartlab.in/group/some-science/forum/topics/science-s-rules...
7.   Ribosomal DNA Copy Number Variation Associates with Hematological Profiles and Renal Function in the UK Biobank, Cell Genomics (2024). DOI: 10.1016/j.xgen.2024.100562. www.cell.com/cell-genomics/ful … 2666-979X(24)00128-9