Smoking linked with higher risk of severe COVID-19 and related death

Smoking is likely to increase the risk of developing severe COVID-19 and dying from the virus, according to new research published in the journal Thorax.

Using data from the UK Biobank alongside that from primary care records, COVID-19 testing, hospital admissions and death certificates, researchers undertook two separate analytical approaches – observational and Mendelian randomisation – to explore the link between smoking and COVID-19 outcomes.

Of 421,469 participants included from the UK Biobank, 13,446 carried out a COVID-19 swab (PCR) test over the study period (January to August 2020), of which 1,649 tested positive, 968 required hospital admission, and 444 died from their infection.

The research team, lead by Dr Ashley Clift, a Clinical Research Fellow at the University of Oxford, determined that 59% of participants had never smoked, 37% had previously smoked and 4% currently smoked, with 71% being classed as light or moderate smokers and 29% as heavy (20+ a day).

An observational analysis showed that current smokers were 80% more likely to be admitted to hospital with COVID-19 than those who had never smoked, and that the heaviest smokers were six times more likely to die as a result of being infected with the virus.

Mendelian randomisation (among 281,105 white British participants) revealed that a genetic predisposition to smoking was linked with a 45% higher risk of COVID-19 infection, a 60% increased risk of related hospital admission and a 10 times higher risk of COVID-related death.

“Overall, the congruence of observational analyses indicating associations with recent smoking behaviours and Mendelian randomisation analyses indicating associations with lifelong predisposition to smoking and smoking heaviness support a causal effect of smoking on COVID-19 severity,” the authors concluded.

Two recent population-level studies in the UK had suggested a protective effect of smoking on COVID-19 severity. However, this study “adds to our confidence that tobacco smoking does not protect against COVID-19 as [the] Mendelian randomisation analyses are less susceptible to confounding than previous observational studies,” noted Dr Anthony Laverty and Professor Christopher Millett, from Imperial College London’s School of Public Health, in an accompanying editorial.

They also highlighted other findings – including from the Real Time Assessment of Community Transmission (REACT) study that smoking was linked with a higher probability of developing long COVID – that taken together reinforce “the existence of the negative impacts of smoking on COVID-19 outcomes.”

“A respiratory pandemic should be the ideal moment to focus collective minds on tobacco control,” they concluded.

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