French researchers find fewer smokers in Covid-19 patients compared to general population. Further research is needed to see if there is a connection between nicotine and lowering the effect of the virus.

Researchers studying Covid-19 patients in the Paris public hospital network have found evidence that smokers could be better protected from the virus than others, though they warn that smoking can aggravate symptoms for those who do contract the illness.

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Researchers from several institutions saw that of the 11,000 or so patients hospitalised in Paris public hospitals for Covid-19 at the start of April, only 8.5 percent were smokers, compared to 25.4 percent of the general public.

They then looked more closely at 482 patients at the Pitié-Salpêtrière hospital in Paris who tested positive for Covid-19 and found a similar phenomeon: the 343 hospitalised for serious complications had a smoking rate of 4.4 percent, and 5.3 percent of the 139 who were sent home with less serious symptoms smoked.

Upon further investigation, accounting for age and sex, the researchers found that the small number of smokers appeared to have had some kind of protection against the virus.

The findings were in line with a study on Covid-19 in China, published at the end of March in the New England Journal of Medicine, that found 12.6 percent of 1,099 people studied, who tested positive for Covid-19 were smokers, while the smoking rate in China is around 28 percent.

Nicotine could be the reason

The French study “confirms that active smokers are protected against the SARS-Cov-2 infection,” writes the press release. “The reasons for this protection are not established, but nicotine could be a candidate.”

The researchers warn that people should not take up smoking, as smokers who do become infected with Covid-19 tend to develop more serious symptoms.

The head of France’s national health agency, Jerome Salomon, said the nicotine link is only an unproven hypothesis at this stage, and warned that smoking remains the number one killer in France, with 75,000 people who die of smoking-related complications each year.

How would it work?

In an upcoming article (in pre-print here) researchers write: “Although the chemistry of tobacco smoke is complex, these data are consistent with the hypothesis that its protective role takes place through direct action on various types of nAChRs [nicotine receptors] expressed in neurons, immune cells (including macrophages), cardiac tissue, lungs, and blood vessels.”

In other words, nicotine could block the virus from entering the body through neurons in the olfactory system or through lung cells.

The hypothesis remains to be proven. The researchers are looking to organise a clinical study using nicotine patches, pending approval from French health authorities.

The study would have three aims: to see if nicotine prevents infection in healthcare workers; to see how it works therapeutically and to lower symptoms in hospitalised patients; and to see its effect on patients in intensive care.

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