Smoking may reduce the likelihood of being hospitalised with coronavirus, claims a study.

Here is the abstract of the study – Smoking, vaping and hospitalization for COVID-19 – by researchers at the University of West Attica in Greece and New York University.

The study presents an analysis of the current smoking prevalence among hospitalized patients with COVID-19 in China, compared to the population smoking prevalence in China (52.1% in males and 2.7% in females). Through a systematic research of the literature (PubMed) we identified 7 studies examining the clinical characteristics of a total of 2352 hospitalized COVID-19 patients that presented data on the smoking status.

The expected number of smokers was calculated using the formula Expected smokers = (males x 0.521) + (females x 0.027). An unusually low prevalence of current smoking was observed among hospitalized COVID-19 patients (8.7%, 95%CI: 7.6-9.9%) compared to the expected prevalence based on smoking prevalence in China (30.3%, 95%CI: 28.4-32.1%; z-statistic: 22.80, P < 0.0001). This preliminary analysis does not support the argument that current smoking is a risk factor for hospitalization for COVID-19, and might even suggest a protective role.

The latter could be linked to the down-regulation of ACE2 expression that has been previously known to be induced by smoking. However, other confounding factors need to be considered and the accuracy of the recorded smoking status needs to be determined before making any firm conclusions. As a result, the generalized advice on quitting smoking as a measure to improve health risk remains valid, but no recommendation can currently be made concerning the effects of smoking on the risk of hospitalization for COVID-19.

No studies recording e-cigarette use status among hospitalized COVID-19 patients were identified. Thus, no recommendation can be made for e-cigarette users.

It makes intuitive sense that smoking ought to exacerbate a respiratory infection such as coronavirus. Indeed, earlier reports in the mainstream media reflected this view when very little was known about coronavirus, pointing out the obvious — that smoking damages your lungs and so do respiratory diseases.

A recent study also reflects this conventional wisdom. Published in the journal of the International Society for the Prevention of Tobacco Induced Diseases, the March COVID-19 and smoking paper states:

…although further research is warranted as the weight of the evidence increases, with the limited available data, and although the above results are unadjusted for other factors that may impact disease progression, smoking is most likely associated with the negative progression and adverse outcomes of COVID-19.

But the authors of the West Attica/NYU study cautiously advance a theory as to why this might not be the case:

Smoking increases susceptibility to respiratory infections and media reports suggest that it may increase the risk of being infected with acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus responsible for COVID-19. SARS-CoV-2 is known to use the angiotensin converting enzyme 2 (ACE2) as a receptor for cell entry, and there is evidence that smoking down-regulates ACE2 expression in the lung and other tissues.

Their findings, though surprising, appear to be supported by the latest statistics from the Centers for Disease Control and Prevention (CDC). These too show that – contrary to expectations – relatively few smokers and ex-smokers have been hospitalised with COVID-19.

The CDC apparently isn’t eager to play up the significance of smoking in patient survival outcomes. Nevertheless, it acknowledges in this throwaway comment:

Finally, for some underlying health conditions and risk factors, including neurologic disorders, chronic liver disease, being a current smoker, and pregnancy, few severe outcomes were reported; therefore, conclusions cannot be drawn about the risk for severe COVID-19 among persons in these groups.

Neither the authors of the Smoking, vaping and hospitalization for COVID-19 study nor the CDC are advocating taking up smoking in order to ward off coronavirus. Also, they caveat their findings by noting that this is preliminary data which may be based on incomplete information.

Other studies

Further, the study authors note that smokers are more likely than non-smokers to ‘suffer comorbidities, such as cardiovascular disease, which are risk factors for adverse COVID-19 outcomes.’

They conclude:

Considering the above-mentioned uncertainties, the generalized advice on quitting smoking as a measure to improve health risk remains valid but no recommendation can be currently made concerning the effects of smoking on the risk of hospitalization for COVID-19.