Obese men are at greater risk of severe Covid-19 and death than obese women, research has suggested.

Data from 3,530 patients in hospital with Covid-19 found that obese men with a body mass index (BMI) of 35 or over had a “significant association with higher in-hospital mortality”, while women with a BMI of 40 or over had this link.

The researchers also found that obesity may be a stronger risk factor for severe Covid pneumonia and the need for a ventilator in men than in women.

In the study, a BMI of 35 to 39.9 was regarded as class II obesity, while 40 and over was regarded as class III.

The authors found that patients with class II and III obesity had a higher likelihood of dying in hospital, especially when compared with patients of normal weight, and this association was stronger the fatter people were.

We suspected there may be an association between body mass index and systemic inflammation... However, we found that this wasn’t the case

These patients were also more likely to develop severe pneumonia and to need to go on a ventilator.

The experts, writing in the European Journal of Clinical Microbiology and Infectious Diseases, concluded: “Obesity classes II and III in men and obesity class III in women were independently associated with higher in-hospital mortality in patients with Covid-19.

“The male population with severe obesity was the one that mainly drove this association.”

The study was carried out by a team at Montefiore Medical Centre in the Bronx, New York, with patients admitted from March 10 to May 1 last year.

Out of the 3,530 patients included in the analysis, 1,579 were women, 896 had a BMI below 25, 1,162 had a BMI of 25–29, 809 had a BMI of 30–34 and 663 had a BMI of 35 or above.

The authors also investigated if systemic inflammation was linked to an increased risk of death.

Dr Arcelia Guerson-Gil, one of the authors of the paper, said: “It is known that a major cause of disease severity and death is an excessive inflammatory response to (Covid) that is associated with high levels of circulating cytokines, such as IL-6.

“Obesity is considered a state of enhanced chronic inflammation, so we suspected there may be an association between body mass index and systemic inflammation as indicated by IL-6 level. However, we found that this wasn’t the case.”

Structural drivers of obesity urgently need to be tackled

The authors found that patients who died from Covid-19 had higher average levels of IL-6 compared with survivors, and men had higher average levels of IL-6 than women. Average IL-6 levels also increased with age.

However, the authors found no clear association between IL-6 and obesity, suggesting that while inflammation may play a role in severe disease and death from Covid-19, it may not be what links it to obesity.

The authors suggested obesity may lead to poor outcomes for Covid due to other factors, such as poorer lung function, increased work of breathing or a higher expression of a receptor called ACE2, which allows Covid to enter cells in fat tissue.

Dr Jamie Hartmann-Boyce, senior research fellow in health behaviours at the University of Oxford, said more work was needed due to the small number of women in the study.

She added: “Larger studies are needed before we can say with any certainty that class II obesity is less of a risk factor in women than in men.

“What we can say for certain now is that obesity is associated with an increased risk of worse Covid-19 outcomes in and of itself, and is a risk factor for conditions such as type 2 diabetes which also predispose to worse outcomes.

“Obesity is a complex, chronic, and relapsing condition and a major contributor to health inequalities. Structural drivers of obesity urgently need to be tackled.”