Coronavirus disease 2019 (COVID-19) has triggered a global pandemic. As of September 30th, 2021, 324 million cases had already been registered worldwide. Several comorbidities are risk factors for COVID-19. Mucosal tissues are the virus's main entry points: the nose, mouth, upper respiratory tract, and, less frequently, conjunctival mucosa.
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Exposure to tobacco smoke triggers inflammatory processes in the lungs, increasing mucosal inflammation and permeability in epithelial cells. It also enhances the expression of inflammatory cytokines and tumor necrosis factor (alpha), causes mucus overproduction and decreases mucociliary clearance. Knowledge of host factors, particularly avoidable host ones such as smoking, may help lower virus contamination and illness severity.
Association of smoking with non-communicable airway diseases
Tobacco smoke, a complex mixture of about 5000 chemicals, carcinogens, and poison, is one of the most common sources of chemically-mediated illness exposure in humans and maybe other living species. Smoking is a risk factor for the onset and progression of many respiratory disorders, including infections.
Tobacco smoking, in particular, is one of the leading causes of respiratory disorders such as chronic obstructive pulmonary disease (COPD) and lung cancer. As smoking disrupts the healing of the respiratory epithelium and reduces bacteria clearance from the airways, it is also an independent risk factor for community-acquired pneumonia (CAP).
According to epidemiological research, Smoking has also been linked to the development of active tuberculosis (TB), a decline in anti-TB immunity, and TB-related mortality.
According to the World Health Organization, lung-related deaths from smoking, including secondhand smoke, totaled 3.3 million in 2017, with 1.5 million people dying from chronic respiratory diseases and 1.2 million dying from cancer (tracheal, bronchus, and lung).
COVID-19 and smoking
Several meta-analyses have already examined the effect of smoking on COVID-19 severity. Due to damage to the upper airways and a decline in pulmonary immune function, smoking and e-cigarette use increase the incidence and severity of lung infections. Smokers, in particular, are at a higher risk of infection and death from Cov-MERS (Middle East Respiratory Syndrome).
Two assessments of the first five studies with smoking and COVID-19 data came to varied findings. Another analysis looked at six published case studies that included data on smoking among COVID-19 patients, but it didn't come to any conclusions about the link between COVID-19 severity and smoking.
There are numerous research papers published on the link between smoking and COVID-19, the respiratory illness caused by the SARS-CoV-2 virus, but the findings drawn are uncertain.
Smoking prevalence may be lower in the general community, according to evidence from hospital COVID-19 cases in China, Padova, Italy, and New York City. The link between smoking and COVID-19 is even more confusing when one considers that smoking is linked to an increased risk of lung cancer and is known to cause a variety of respiratory ailments. The patient's smoking history is one risk linked to the advancement of COVID-19 pneumonia.
Data from a retrospective study (China)
As previously stated, smoking has been demonstrated to impair the immune response within the respiratory system, making smokers more susceptible to pathogenic infections. Between December 30, 2019, and January 15, 2020, 78 COVID-19 patients were admitted to three hospitals in Wuhan, China, for a retrospective cohort study.
Patients with a history of smoking had a significantly higher proportion of rapid deterioration in health during their admission than non-smokers (27% versus 3%, p = 0018), suggesting that smoking may negatively impact COVID-19 prognosis.
Another retrospective cohort analysis on 140 confirmed COVID-19 patients admitted to Wuhan's No. 7 Hospital between January 16 and February 3, 2020, indicates a link between smoking and severe manifestations of the disease. Older age, a higher body temperature at admission, a faster respiratory rate, lower albumin, and a raised C-reactive protein level were all linked to COVID-19 progression.
COVID-19 and smoking: Data suggesting otherwise
While the majority of research to date has found a link between smoking and worsening COVID-19 symptoms, some reports have found an inverse relationship between smoking and COVID-19 symptoms. The smoking prevalence among COVID-19 patients has been reported to be lower than that of the general population.
Two preliminary systematic reviews looked into the effects of smoking on COVID-19 severity and found a negative link. Despite a trend toward higher risk, a meta-analysis of 1399 patients with confirmed COVID-19 illness severity indicated no significant link between smoking and COVID-19 disease severity.
When controlled for age and sex, one of the largest cohort studies published to date in the UK found an increased incidence of in-hospital COVID-19 death in ex-smokers compared to never-smokers. Even after accounting for additional risk variables such as BMI, chronic respiratory disorders, diabetes, hypertension, and chronic heart disease, this link was shown to be substantial. According to their report, the decrease in risk was majorly due to the adjustment for chronic respiratory disease, which is closely linked to cigarette smoking.
After controlling for potential confounders such as economic activity, the rate of COVID-19 testing, and the strength of containment policies, another study found a statistically significant negative correlation between the level of smoking in the adult population and the prevalence of reported COVID-19 cases as of May 30, 2020, across 36 European nations. There was no link between smoking prevalence and COVID-19 mortality per million people, according to the data.
While research into the pathophysiology of COVID-19 is still in its early stages, multiple studies have found a link between tobacco smoking and a worsening of illness prognoses in COVID-19 patients.
More research is needed to confirm these preliminary findings and to determine the mechanisms underlying the appearance of more severe COVID-19 symptoms among smokers. Furthermore, no convincing indication of an increased vulnerability to SARS-CoV-2 infection due to smoking has been found to date, and future epidemiological research will need to look into this further.
- Shastri, M. D., Shukla, S. D., Chong, W. C., Kc, R., Dua, K., Patel, R. P., Peterson, G. M., & O'Toole, R. F. (2021). Smoking and COVID-19: What we know so far. Respiratory medicine, 176, 106237. https://doi.org/10.1016/j.rmed.2020.106237
- Reddy, R. K., Charles, W. N., Sklavounos, A., Dutt, A., Seed, P. T., & Khajuria, A. (2021). The effect of smoking on COVID-19 severity: A systematic review and meta-analysis. Journal of medical virology, 93(2), 1045–1056. https://doi.org/10.1002/jmv.26389
- Tsigaris, P., & Teixeira da Silva, J. A. (2020). Smoking Prevalence and COVID-19 in Europe. Nicotine & tobacco research: official journal of the Society for Research on Nicotine and Tobacco, 22(9), 1646–1649. https://doi.org/10.1093/ntr/ntaa121
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- Patanavanich, R., & Glantz, S. A. (2020). Smoking Is Associated With COVID-19 Progression: A Meta-analysis. Nicotine & tobacco research: official journal of the Society for Research on Nicotine and Tobacco, 22(9), 1653–1656. https://doi.org/10.1093/ntr/ntaa082