The coronaviruses that have spread across the globe for the past two decades all attacked the respiratory system, mainly affecting breathing and gas exchange. They cause respiratory tract infections that can range from mild to lethal. Mild illnesses include some cases of the common cold, while more lethal varieties can cause SARS, MERS, and the coronavirus disease (COVID-19). COVID-19, which is actively spreading across the globe, has sickened more than 2.4 million people and has now become a significant threat to healthcare systems in most countries.
The fatality rate among infected people increases among the elderly and those with underlying medical conditions. Now, a new study published as a pre-print on medXriv, links smoking to the progression of COVID-19 disease, suggesting that the odds of disease progression is more than double in smokers.
Study: Smoking is Associated with COVID-19 Progression: A Meta-Analysis. Image Credit: Wavebreakmedia / Shutterstock
Smokers at risk
Smoking has many adverse health effects and had been tied to several conditions, such as cardiovascular disease, lung cancer, and chronic obstructive pulmonary disease (COPD). The researchers from the University of California San Francisco wanted to determine the link between smoking and COVID-19 progression.
Smoking and e-cigarette use may increase the risk of respiratory infections since the chemicals in them cause damage to the upper airways and reduce airway immune function. Previous studies have linked a higher risk of infection and mortality in cases of the Middle East respiratory syndrome (MERS), which is similar to COVID-19 and was first reported in Saudi Arabia in 2012.
To arrive at their findings, the team of researchers identified 12 research papers about smoking and its connection with COVID-19. They run a search using the PubMed database using the terms, smoking, characteristics, risk factors, outcomes, smoker, COVID, COVID-19, SARS-CoV-2, sars cov 2, and coronavirus. The research they found were published between January 1 2020 and April 6 2020, providing a total of 396 studies. Of these, only 12 were eligible to be included in the study, 10 of which were from China, one from the United States, and the other one was from South Korea.
In these twelve papers, collectively, there were 9,025 patients with coronavirus disease, where 9.7 percent had severe disease, and 5.5 percent had a history of smoking.
The analysis shows that smoking is a risk factor for COVID-19 progression, with those who smoke having 2.25 times the risk of developing severe COVID-19 outcomes than non-smokers. The findings of the study are contradictory to an earlier study, which includes only five studies. The result is not surprising since smoking has long been associated with respiratory diseases due to a weakened pulmonary immune function.
“Smoking is a risk factor for progression of COVID-19, with smokers having higher odds of COVID-19 progression than never smokers. Physicians and public health professionals should collect data on smoking as part of clinical management and add smoking cessation to the list of practices to blunt the COVID-19 pandemic,” the researchers wrote in the paper.
Smoking and pulmonary immune function
A previous study has noted that tobacco smoke induces and alters immune responses in the lungs, triggering inflammation, asthma, allergy, and other lung diseases.
The study highlights the effect of cigarette smoke on the immune system, contributing to the development of lung diseases, including COPD. Tobacco smoke has also been linked to asthma and allergic diseases in children, while it has also been tied to a multitude of inflammatory processes that lead to inflammation. Aside from inflammation, other effects include a higher risk of infection, allergies, and tissue damage.
Further, the study unveiled how the imbalance between oxidants and antioxidants as a result of tobacco smoke exposure may lead to oxidative stress, increased expression of inflammatory cytokines, and increased mucosal inflammation, all leading to respiratory ailments.
The findings clearly show that smoking is closely related to COVID-19 severity, and smoking history should be added to the clinical management of the coronavirus infection. Stopping smoking may help reduce the risk of having severe COVID-19 and should be part of the list of measures to curb the global pandemic.
COVID-19 by the numbers
The coronavirus disease has affected many countries worldwide, with the western countries reporting the highest number of infections. As of writing, there are more than 2.3 million confirmed cases and more than 161,000 deaths. A majority of the deaths were elderly and those with underlying medical conditions.
The highest number of cases and deaths per country is in the United States, reporting more than 759,000 cases and more than 70,000 deaths. The country is the hardest hit by the global pandemic, followed by Spain with more than 198,000 cases and more than 20,000 deaths, Italy with more than 178,000 cases and more than 23,000 deaths, and France with more than 154,000 cases and more than 19,000 deaths, among others.
- Patanavanich, R., and Glantz, S. (2020). Smoking is Associated with COVID-19 Progression: A Meta-Analysis. medRxiv. https://www.medrxiv.org/content/10.1101/2020.04.13.20063669v1
- Strzelak, A., Ratajczak, A., Adamiec, A., and Feleszko, W. (2018). Tobacco Smoke Induces and Alters Immune Responses in the Lung Triggering Inflammation, Allergy, Asthma, and Other Lung Diseases: A Mechanistic Review. International Journal of Environmental Research and Public Health. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5982072/