Smoking is highly likely to worsen the severity of COVID-19 and the risk of dying from the virus, researchers report today in a study aimed at dispelling another pandemic myth.
A large UK Biobank study, published in today’s Thorax, is the first to pool observational and genetic data on smoking and COVID-19. Previous research on whether or not smoking is associated with a greater likelihood of more severe illness has been inconsistent.
Several studies 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 the infection.
Most of the research up until now has been observational, so for this study, the researchers, at Oxford University’s Nuffield Department of Primary Care Health Sciences, combined observational and Mendelian randomisation analyses to better understand the relationship.
They examined linked primary care records, COVID-19 test results, hospital admissions data and death certificates to look for associations between smoking and COVID-19 infection severity from January to August 2020 in 421,469 participants of the UK Biobank.
During the study period, 13,446 (3.2%) people took a COVID-19 PCR test, of whom 1,649 (0.4%) tested positive. Of these, 968 (0.2%) needed hospital treatment and 444 (0.1%) died from the virus.
Those who had never smoked accounted for 59% of the participants, while 37% were former smokers and 4% were current smokers. Among the current smokers, 71% smoked between one and 19 cigarettes a day and 29% smoked 20 or more cigarettes a day.
’Improbable’
The researchers found that current smokers were 80% more likely to be admitted to hospital and significantly more likely to die from COVID-19 than those who had never smoked.
They also used Mendelian randomisation to assess whether or not a genetic predisposition to smoking and heavy smoking might have a role in COVID-19 severity among 281,105 of the original participants living in England.
This showed that a genetic predisposition to smoking was associated with a 45% higher risk of infection and a 60% higher risk of hospital admission for COVID-19, and that a genetic predisposition to smoke more heavily was associated with a more than doubling in the risk of infection, a five-fold increase in the risk of hospital admission, and a 10-fold increase in the risk of death from the virus.
Researcher Dr Ashley Clift said: “Our results strongly suggest that smoking is related to your risk of getting severe COVID, and just as smoking affects your risk of heart disease, different cancers, and all those other conditions we know smoking is linked to, it appears that it’s the same for COVID.”
Writing in the journal, Drs Anthony Laverty and Christopher Millet, of Imperial College, London, state: “The idea that tobacco smoking may protect against COVID-19 was always an improbable one.”
Clift AK, von Ende A, San Tan P et al. Smoking and COVID-19 outcomes: an observational and Mendelian randomisation study using the UK Biobank cohort. Thorax 28 September 2021
Leave a Reply