Many studies have shown a low prevalence of smokers in hospitals with COVID-19.
When smokers do get diagnosed with the virus, however, they appear to be more likely to get so sick that they need ventilation, two studies in the review showed.
If the findings are proven, scientists say it’s likely that it is not cigarettes – filled with thousands of harmful chemicals – that would offer a potential protection, but the nicotine that is beneficial.
A theory touted by scientists is that nicotine reduces ACE-2 receptors, which are proteins in the body the virus binds to in order to infect cells.
The coronavirus enters cells inside the body via the structures, which coat the surface of some cells, including in the airways and lungs.
If nicotine does lowers ACE-2 expression, it makes it harder for viral particles to gain entry into cells and therefore cause an infection.
On the other hand, other studies show that nicotine enhances the action of the ACE-2 receptor, which in theory, puts smokers at a higher risk of contracting the coronavirus.
Other scientists say low levels of ACE-2 expression as a result of nicotine may prevent worse damage from viral infection, and there is no evidence that says higher quantities of ACE-2 receptors increases the risk of SARS-CoV-2 infection in the first place.
Dr Konstantinos Farsalinos, from the University of West Attica, Greece, who queried whether nicotine could be a cure for COVID-19 in a paper published on May 9, said: ‘Up-regulation of ACE2, though seemingly paradoxical, may in fact protect patients from severe disease and lung injury.’
A 2008 study in mice found that getting rid of ACE-2 made the animals more likely to suffer severe breathing difficulties when infected with the SARS virus, which is almost identical to COVID-19.
Other scientists have turned their head towards nicotine’s ability to prevent inflammation, where evidence is more robust.
Nicotine has been shown inhibit the production of pro-inflammatory cytokines, such as TNF, IL-1 and IL-6, which are involved in promoting an inflammatory response.
A ‘cytokine storm’ is a phenomenon in which an abundance of cytokines are released in response to infection.
Doctors have previously said that it’s often the body’s response to the virus, rather than the virus itself, that plays a major role in how sick a person gets.
A cytokine storm can lead to respiratory failure and the attack of healthy tissues, causing multi-organ failure.
Therefore, the cytokine storm is being looked at as a target for COVID-19 treatment.
‘Nicotine has effects on the immune system that could be beneficial in reducing the intensity of the cytokine storm,’ Dr Farsalinos wrote in Internal and Emergency Medicine.
‘The potential benefits of nicotine…. could explain, at least in part, the increased severity or adverse outcome among smokers hospitalized for COVID-19 since these patients inevitably experience abrupt cessation of nicotine intake during hospitalization.
‘This may be feasible through repurposing already approved pharmaceutical nicotine products such as nicotine patches.’
Dr Nicola Gaibazzi, who recently published findings on MedRxiv of ‘very low’ numbers of smokers in Italian COVID-19 patients, speculates smoke exposure may bolster the immune system.
He said exposure to cigarette smoke reduces the body’s immune system over time, measured by lower inflammatory markers.
Therefore, when smokers are infected with a virus like SARS-CoV-2, their immune system is more ‘tolerant’ and does not overreact.
On the other hand, non-smokers may be more prone to having the sudden and deadly cytokine storm when they are infected with the virus.
Scientists have stressed that the evidence supporting nicotine as a medicine does not mean everyone should take up smoking.