Researchers have identified genetic evidence to support a causal link between smoking and obesity and an increased risk of severe COVID-19 and sepsis.

The study, led by an international team of scientists from the UK, Norway and the USA, found that both smoking and having a higher body mass index (BMI, a measure of obesity) can increase the risk of severe outcomes with COVID-19.

Our work supports that something can be done to reduce risk of severe COVID-19, and in particular that losing excess weight and stopping smoking can make a difference. Dr Dipender Gill School of Public Health, Imperial College London

The same was also true for the risk of developing sepsis, a dangerous inflammatory response to infection, which many patients with severe COVID-19 also experience.

According to the researchers, the findings highlight how measures such as quitting smoking and losing weight can help reduce the risk of severe health outcomes.

Dr Dipender Gill, from Imperial’s School of Public Health and a clinician at St George’s Hospital in London, said: “While it’s already known that smoking and obesity increase the risk of many serious health conditions, including heart disease, stroke and certain types of cancer, our findings highlight that the implications of smoking and obesity are exacerbated in the current COVID-19 pandemic.

Reducing environmental factors

In the study, published this month in the journal Circulation, the team used a statistical technique called Mendelian Randomization to uncover the causal link.

Using two datasets for several thousands of patients with severe COVID-19 and sepsis, they looked for small genetic variations known to be associated with smoking and obesity.

By using these variants as genetic proxies, the technique helps to rule out the influence of confounding factors, such as diet and lifestyle, which can otherwise influence observational studies.

The researchers found that on average, COVID-19 patients who had genetic variants linked with smoking or obesity were more likely to have worse outcomes from the disease. The same causal link was also uncovered when they searched for the variants in a database of sepsis patients.

According to the researchers, there are various mechanisms by which smoking and obesity may elevate the risk of suffering from severe COVID-19 and sepsis, including through disrupting the regulation of inflammation and the immune response.

“Our work supports that something can be done to reduce risk of severe COVID-19, and in particular that losing excess weight and stopping smoking can make a difference,” added Dr Gill.

“Now, more than ever, it’s essential that campaigns highlighting the benefits of losing excess weight and stopping smoking remain central to public health strategies.”

This article is based on materials from St George’s, University of London.

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‘Cardiometabolic Traits, Sepsis and Severe COVID-19: A Mendelian Randomization Investigation’ by Ponsford, MJ. et al. is published in the journal Circulation. DOI:10.1161/CIRCULATIONAHA.120.050753