Being fat triggers a 'troublesome' immune response to Covid-19, scientists fear as government SAGE committee investigates why obesity raises the risk of death

Being fat triggers a 'troublesome' immune response to COVID-19, scientists fear.

Scientists advising Government ministers are exploring potential underlying mechanisms that could increase the risk of death for obese patients.

According to data from intensive care units, people of a healthy weight make up a minority of critically ill COVID-19 patients. Almost three quarters are carrying extra weight.

And NHS hospital data this week revealed obesity raises the risk of dying from coronavirus by nearly 40 per cent.

While the reasons remain unclear, scientists have warned of a potential dysfunctional immune system that makes fighting the virus more difficult.

Fat cells - of which there are more in the tissues of obese people - may harbour vital immune cells, reducing their availability in the rest of the body.

Or it may swing the other way - the immune response may go into overdrive, known as a cytokine storm, which is thought to play a major role in COVID-19 death.

There hasn't been data to suggest obese people are more likely to catch the killer virus in the first place. 

Being fat triggers a 'troublesome' immune response to COVID-19, scientists fear, as government SAGE committee investigates why obesity raises the risk of death

According to the ICNARC report, people of a healthy weight make up a minority of critically ill COVID-19 patients. Almost three quarters are carrying extra weight (BMI of 25 to 40+)

The Sunday Times reports that the SAGE committee will investigate the relationship between obesity and serious COVID-19 illness.   

As the death toll of the virus in the UK reaches more than 28,000, data collecting from NHS hospitals has revealed those most at risk. 

It includes those with obesity, those with underlying health conditions, and people of BAME backgrounds. Men also account for more than 70 per cent of patients. 

There are a higher proportion of people with obesity in critical care than in the general population, according to the Intensive Care National Audit and Research Centre, which collects data from NHS hospitals. 

The figures, released on Friday, are based on a sample of 7,542 critically-ill patients confirmed as having Covid-19.   

According to the ICNARC report, people of a healthy weight make up a minority of critically ill COVID-19 patients.

Almost three quarters (73 per cent) are carrying extra weight. 

Some 35 per cent have a BMI between 25 and 30, which is regarded as 'overweight' by the NHS, 31 per cent are obese, and just over seven per cent are severely obese.

For comparison, in the general population of England, 64.3 per cent of adults are either overweight (35.6 per cent) or obese (28.7 per cent), Government data from 2019 shows.   

There are more morbidly obese people in critical care (7.32) than in the population (3.6 per cent in England).

Dr Dyan Sellayah, a lecturer in cellular and organismal metabolism, University of Reading, said: 'What we know from the data so far is that obesity is a clear risk factor for severe disease.

'Obese people tend to have dysfunctional immune systems – their fat tissue for example becomes a reservoir for immune cells known as macrophages. 

'While these cells reside in our fat under normal circumstances, in obesity they are at higher frequency and become more troublesome (they start to secrete inflammatory cytokines) and negatively impact on immune and metabolic health. 

'It is likely that the immune response to the virus is therefore ineffective in obese individuals, which may explain why people from BAME backgrounds who have higher incidence of obesity are vulnerable to the virus.'

Studies have shown obese people are more likely to suffer serious complications or die from infections, such as the flu, because their immune systems are constantly ramped up as they try to protect and repair the damage inflammation causes to cells.

Using all its energy fending off inflammation means the body's defence system has few resources left to defend against a new infection like COVID-19. 

Obesity is one of the main risk factors for comorbidities, including heart disease, diabetes and high blood pressure - all of which have been identified as common medical conditions among COVID-19 patients.

People with underlying health conditions are more vulnerable to serious illness from the virus.  

Research published this week, considered to be the largest of its kind in Europe, revealed more than half (53 per cent) of COVID-19 patients in the UK had at least one comorbidity.

Almost a third (29 per cent) had heart disease - conditions which block blood vessels and make it hard to pump blood and oxygen around the body.

Nearly a fifth (19 per cent) were diabetic, the same number had lung disease, 15 per cent suffered from kidney disease and 14 per cent were asthmatic.

The same report revealed that once in hospital, survival rates may be lower among obese people. 

The analysis of 17,000 COVID-19 admissions found death rates were 37 per cent higher among obese patients, second only to dementia (39 per cent) but more than heart disease (31 per cent).   

The research was conducted by a team of Britain's top infectious diseases scientists who are part of the pandemic-planning global body.

Researchers analysing almost 17,000 COVID-19 admissions revealed obesity raises the risk of dying from coronavirus by nearly 40 per cent. More than half (53 per cent) of hospitalised patients had at least one comorbidity (which are pictured). The most common was heart disease (29 per cent), diabetes (19 per cent), lung disease (19 per cent) kidney disease (15 per cent) and asthma (14 per cent)

Reduced lung function and inflamed tissue under the skin and around internal organs could be linked to the increased risk, according to the team. 

They found both factors can trigger a life-threatening over-reaction of the body's immune response that causes harm to patients.

Cytokines are chemical-signalling molecules which guide a healthy immune response. They tell immune cells to attack viral molecules in the body.  

But in some people, this response goes into overdrive and immune cells start attacking  healthy tissue as well, known as a cytokine storm.  

Fredrik Karpe, professor of metabolic medicine at Oxford University, said if you 'have a big belly', this can be problematic when lying down.

The weight of stomach fat pushes the diaphragm upwards, reducing lung volume. 

COVID-19 is a respiratory disease which in severe cases, affects lung function. Therefore restricted lung capacity would exacerbate symptoms.

If lung function has already deteriorated, oxygen in the blood is of limited supply which can affect vital organs, such as the heart.  

Dr Sellayah also explained that people who have extra weight have more cells that demand oxygen to work, reducing the amount available to organs further. 

He said: 'As your infection progresses and the virus infects more and more cells, the demand for oxygen in the tissues is much higher for an obese individual than it is for a lean individual. 

'Eventually the obese body becomes overwhelmed by the lack of oxygen getting to the major organs.' 

As the country is gripped by the coronavirus crisis, being overweight and its associated health risks are being highlighted as never before. 

Last week a British NHS doctor claimed today that Prime Minister Boris Johnson was so badly affected by coronavirus because he is 'significantly' overweight.

Consultant cardiologist Dr Aseem Malhotra said there is a ten-fold risk of death from the disease - which has so far killed more than 20,000 Britons - if patients are obese.

He pointed out that other 'slimmer' members of the Cabinet - like Health Secretary Matt Hancock - recovered much more quickly and were not hospitalised.

Other top Government officials and advisers who have recovered from the virus include Chief Medical Officer Chris Whitty, Chief Adviser Dominic Cummings and Health Minister Nadine Dorries. 

Mr Johnson, 55, has long struggled with his weight and in 2018 revealed he weighed almost 16 and a half stone, which at 5ft 9in puts him in the high risk category.

Dr Malhotra said: 'It was obviously very concerning for the whole nation to see our Prime Minister get admitted to hospital with COVID-19.

'Now it is an observation, but it does fit with the evidence, Boris unfortunately is significantly overweight.

'I used to speak with one of his very senior advisers when he was London Mayor a few years ago who expressed to me personally concerns about his weight.'

There has not been evidence so far to suggest those with obesity are more likely to catch the virus in the first place.

However, some scientists have said now is a good time to try and lose weight in light of the pandemic. 

Professor Neil Ferguson, an Imperial College epidemiologist advising the Government, told The Sunday Times: 'It is always better to stay fit and healthy.

'We need to assess our risks from a personal perspective, including getting fit and losing weight.'