Smoking is one of the major risk factors for several chronic diseases and despite efforts to address the habit, the numbers keep going up. Generally, it increases the risk of developing chronic diseases and the overall complications associated with these diseases and drastically reduces quality of life. Apart from cancer and respiratory conditions, smoking is also a risk factor for metabolic, cardiovascular, reproductive, and various other systemic diseases. Scientists also strongly established the connection between smoking and gastrointestinal (GI) and neuropsychiatry (NP) conditions taking into consideration the brain-gut axis.
Smoking Cigarettes
The long-term inhalation of tobacco and tobacco products disrupts cell multiplication, immune responses, and the function of the endothelial cells. Tobacco contains chemicals like carbon monoxide, aldehyde, nicotine, and some heavy metals. These toxins cause the production of reactive oxygen species (ROS) and free radicals which also cause cellular damage.
Effect of tobacco on the GI and CNS
In the GI, the toxins cause chronic inflammation, reduce blood flow to the intestinal wall, encourage the multiplication of H. Pylori, lower gastric pH, disrupt mucous secretion, and promote poor healing of any ulcers that may develop. These lead to various disease conditions like peptic ulcer disease, the common types of inflammatory bowel disease which are Crohn’s disease and ulcerative colitis, and various GI cancers. Smoking also causes the lower esophageal sphincter to relax leading to gastroesophageal reflux disease.
Smoking increases the risk of developing anxiety disorders, dementia, and psychotic disorders like schizophrenia, and depression. Just like in GI diseases, smoking causes oxidative stress which has been said to lead to varying degrees of chemical dysfunction in the brain. Interestingly, lead from tobacco is said to be a risk factor for coming down with schizophrenia. Reports say that smoking increases the risk of developing neuropsychiatric diseases by two to five times.
Genetic activity spotted
Jiayi Xiong et al. conducted research that analyzed the genetic basis of how tobacco smoking causes 42 GI and NP diseases. We know that smoking is a risk factor for various GI and NP disorders and these disorders are entwined in the brain-gut axis. However, the exact genetic pathway hasn’t been fully understood and that was the driving force behind the study.
They utilized genome-wide association studies (GWAS) that contained over 280,000 smokers and 180,000 non-smokers. It also contained over 80,000 people of European origin who had GI and NP diseases. Interestingly, after analysis, they found out that only GERD had a significant genetic link with smoking. They also established a potential genetic link between schizophrenia and smoking, though the link wasn’t so strong. Previous research done on the subject hadn’t even found any link at all. They suggest that smoking can affect certain genes that regulate neural cell growth leading to the occurrence of disease.
Clinical significance
Smoking significantly affects GI and NP health through various mechanisms as discussed above. In as much as we have various incremental smoking cessation programs, the need to put a full halt to the habit cannot be overemphasized. Even chronic smokers are offered a boost in health and an increase in life expectancy once they successfully quit smoking.
The establishment of genetic relationships between smoking and GI and NP diseases gives us more insight into the pathogenesis and progression of these diseases. It also means that, possibly, targeting specific genetic loci, their mRNA transcripts or their protein derivatives can reduce the severity of these diseases or even their occurrence as a whole.
References
Xiong, J., Wang, Z., Huang, Y., Zhang, S., Yang, G., Yang, J., Gao, S., Wang, T., Li, J., Zhao, G., & Li, B. (2024, May 10). Genetic correlation and causality between smoking and 42 neuropsychiatric and gastrointestinal diseases. medRxiv (Cold Spring Harbor Laboratory). https://doi.org/10.1101/2024.05.09.24307140
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