Smoking, nicotine and Covid-19: What is going on?
The world is enduring the worst crisis since the 1940s, and people are desperate for some good news. Could that good news come from a most unlikely source? Could smoking, or more precisely nicotine, have benefits in controlling the symptoms of Covid-19, the disease caused by the coronavirus SARS-CoV-2? There is emerging, though inconclusive, evidence that nicotine may have protective effects in preventing severe symptoms of Covid-19. If this turns out to be true, it would be extraordinarily good news—nicotine in its medical and recreational forms is widely available and easily affordable.
The picture is quite complicated, but discussion should start with clarity about which outcomes may be improved. There are at least four relevant stages: infection (simply contracting the disease, often with mild symptoms); hospitalization (serious symptoms); admission to an intensive care unit (ICU) (life-threatening symptoms); and finally death. If there is a protective effect, the data suggest it reduces the number reaching hospitalization. For the purposes of fighting the pandemic and returning to economic normality, preventing the onset of symptoms serious enough for hospitalization is the highest priority.
There are two main strands of evidence that suggest a protective effect: the apparent underrepresentation of smokers in Covid-19 hospital admissions and evidence from human biology.
Most Covid-19 studies recording hospitalization and smoking status show smokers are strikingly underrepresented compared to the number that would be expected given smoking prevalence in the population. Being a smoker appears to make it less likely that a Covid-19 sufferer will end up in the hospital. There are many doubts and questions about the reliability of this data, but the effect is remarkably consistent across countries where the data is available. Greek cardiologist Konstantinos Farsalinos and his collaborators examined the literature available on April 25, 2020, to assess the smoking status of those entering the hospital with Covid-19 (see Farsalinos et al., “Prevalence of Current Smoking and Association with Adverse Outcome in Hospitalized Covid-19 Patients: A Systematic Review and Meta-Analysis”).
An unexpectedly low prevalence of current smoking was observed among hospitalized patients with Covid-19. Hospitalized current smokers had higher odds compared to noncurrent smokers but lower odds compared to former smokers for an adverse outcome.
These data suggest that fewer smokers are entering the hospital than we might expect, but once they are admitted, their outlook is worse. This is consistent with other findings showing a worse outlook for smokers once hospitalized. (For example, Vardavas and Nikitara, “Covid-19 and Smoking: A Systematic Review of the Evidence.”)
Notably, in the largest study that assessed severity, there were higher percentages of current and former smokers among patients that needed ICU support, mechanical ventilation or who had died and a higher percentage of smokers among the severe cases.
These authors did not draw attention to just how few smokers there were among the patients to start with—but that is the remarkable fact picked up by Farsalinos and his group. So, what could be going on? Farsalinos and colleagues have a theory:
“The possibility that nicotine may have a protective effect in Covid-19, which may be masked by smoking-related toxicity and by the abrupt cessation of nicotine intake when smokers are hospitalized, should be explored.”
So, it may be that nicotine is protecting smokers up to the point where they are admitted to the hospital. However, all respiratory wards require smoking cessation on admission, so smokers make an abrupt withdrawal from nicotine use. To understand what is happening, it is necessary to separate the effects of decades of smoke exposure, which may be causing underlying vulnerabilities through cardiovascular disease and other stresses, from the effect of nicotine, which may be protective. These two effects of smoking—one harmful, one protective—could be pushing against each other and may become relevant at different points in the progression of the disease.
Clive Bates – Tobacco Reporter – June 1, 2020.