Smoking increases the risk of death from Covid and serious illness

Smoking is more than likely to worsen the severity of Covid-19 and therefore the risk of dying from the infection.

This is assured by one according to a large study that has analyzed data from almost half a million people from the UK Biobank and that has been published in the respiratory journal.

This is the first study of its kind to bring together genetic and observational data on smoking and Covid-19 to strengthen the evidence base.

The evidence on whether smoking is associated with a greater chance of having a more severe Covid has been inconsistent, the researchers note.

Although smoking increases the severity of Covid-19, paradoxically the number

smokers infected with SASR-CoV-2 has been less than that of non-smokers.

Studies conducted early in the pandemic reported a lower prevalence of active smokers among people admitted to hospital with Covid-19 than in the general population. But other population-based studies have suggested that smoking is a risk factor for infection.

The answer to the lower incidence of Covid in smokers was provided last week in a study published in the journal
«Scientific Reports
», Where researchers from the
Hiroshima University (Japan)
found that the extract from cigarette smoke contains a substance that can suppress the expression of ACE2 in mammalian cells and by doing so reduce the ability of the SARS-CoV-2 virus to enter the cell.

This is the first study of its kind to bring together genetic and observational data on smoking and Covid-19 to strengthen the evidence base.

This new work has combined observational and Mendelian randomization to better understand the relationship.

The Mendelian randomization, explain the researchers of the
Oxford University (UK)
, is a technique that uses genetic variants as substitutes for a particular risk factor, in this case genetic variants that make someone more likely to smoke or smoke more heavily, to obtain genetic evidence to support a causal relationship.

The scientists relied on primary care records, Covid-19 test results, hospital admissions data, and death certificates to look for a link between smoking and the severity of infection in 421,469 UK Biobank participants, who had previously had their genetic profile analyzed when they agreed to participate in this trial.

And the results found a clear and consistent relationship between smoking and risk of severe coronavirus using both models, the study concludes.

During the trial period, 13,446 (3.2%) people underwent PCR, 1,649 (0.4%) of whom were positive; 968 (0.2%) required hospital admission, and 444 (0.1%) died as a result of their infection.

Smokers were 80% more likely to be admitted to the hospital and significantly more likely to die from Covid-19

The majority (59%) of the participants had never smoked; more than a third (37%) were ex-smokers, and only 4% smoked. Among the latter, the majority (71%) were light or moderate smokers (1-19 cigarettes / day), and only 29% were heavy smokers (20 + / day).

Compared to those who had never smoked, smokers had a 80% more likely to be admitted to the hospital and significantly more likely to die from Covid-19.

The investigators used Mendelian randomisation to assessr if a genetic predisposition to smoking and heavy smoking could play a role in the severity of Covid-19 Come in 281.105 of participants living in England.

And they saw that there was a genetic predisposition to smoking that was associated with a 45% higher risk of infection and 60% higher risk of hospital admission by Covid-19.

The data also showed that a genetic predisposition to be a heavy smoker was associated with more than double the risk of infection; an increase de 5 times the risk of hospital admission and a tenfold increase in the risk of death from the virus.

The authors admit that their research has some limitations. For example, during the study period the covid tests focused on hospitalized patients. «In addition, the data set used for the observational analyzes (biobank) contains people who tend to be more ‘healthy‘than the general population; and all are of middle or advanced age ”, they admit.

But they conclude that the congruence of the observational analyzes indicating associations with recent smoking behaviors and the analyzes [de aleatorización mendeliana] that suggest a relationship between the predisposition to smoke throughout life and its intensity support a causal effect of this habit on the severity of the disease.

“The idea that smoking tobacco could protect against Covid-19 was always unlikely,” they say Anthony Laverty y Christopher Millet, of the
Imperial College London
, in a linked editorial.

“A respiratory pandemic should be the ideal time to focus efforts on tobacco control,” they add.

The principal investigator, Ashley Clift, concludes. “Our results suggest that smoking is related to the risk of severe Covid and the risk of heart disease, different cancers. So now could be as good a time as any to quit and quit smoking.

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