Tuesday, 2 Mar 2021

Being overweight 'increases risk of severe Covid-19 by at least 40%'

Being overweight raises the risk of severe Covid-19 by at least 40%, finds study of English patients – and obese people may be 70% more likely to end up in hospital if they catch the disease

  • Researchers analysed data from more than 300,000 people in England 
  • They found extra weight is linked with ‘higher odds’ of admission to hospital
  • Even being only overweight (BMI of 25 to 30) raised the risk by 40%
  • It came after a report by Public Health England last month warning of the risks 

Being overweight can raise the risk of severe Covid-19 by 40 per cent, while obese people are 70 per cent more likely to be hospitalised with the disease, according to a study.

Researchers analysed data from more than 300,000 people, 640 of whom ended up in hospital with the coronavirus at the peak of the pandemic.

They found extra weight is linked with ‘higher odds’ of admission to hospital, increasing in line with body mass index (BMI) – a height-to-weight ratio. 

Being too thin also raised the risk compared to someone who was a healthy weight, but by a smaller margin of six per cent. 

The team, led by University College London, sought to build on previous smaller-scale studies which first shone a light on the link between weight and Covid-19.

Concerns led to an investigation by Public Health England, which last month said it found overweight people are more than three times as likely to die of Covid-19 than those of a healthy weight.

The findings are concerning because a massive two in three English adults are overweight or obese, putting them at higher risk from coronavirus.

Last month Prime Minister Boris Johnson launched a new strategy to tackle obesity in the wake of Britain’s death toll – the highest in Europe.

He acknowledged that he was ‘way overweight’ when he was admitted to intensive care in April as he battled Covid-19.

Obesity increases the risk of severe Covid-19 by up to 70 per cent, and being overweight by 40 per cent, according to a study of English people who were hospitalised with the disease

It has been speculated that Britain’s death toll – currently standing at almost 47,000 – could be partially blamed on the country’s high levels of obesity.

Britain is one of the fattest nations in Europe and now has the largest total Covid-19 death toll.

Almost two-thirds of adults in the UK – 64 per cent – are living with excess weight for their height, which is forecast to rise in the next four years without interventions. 


Body mass index (BMI) is a measure of body fat based on your weight in relation to your height.

For children and young people aged 2 to 18, the BMI calculation takes into account age and gender as well as height and weight.

Ethnicity can also affect the risk of some health conditions. For example, adults of Asian origin may have a higher risk of health problems at BMI levels below 25.

Standard Formula:

BMI = (weight in pounds / (height in inches x height in inches)) x 703

Metric Formula:

BMI = (weight in kilograms / (height in meters x height in meters))


Under 18.5: Underweight

18.5 – 24.9: Healthy

25 – 29.9: Overweight

30 or greater: Obese


The researchers led by UCL found that, compared to those of a normal weight (BMI 18.5 – 24.9), the risk of Covid-19 hospitalisation raised by the following:

Under 18.5: 6%

25-30 (overweight): 40%

30-35 (obese): 70%

More than 30 (severely obese): 240%   

The authors of the UCL study warned: ‘Since over two-thirds of Westernised society are overweight or obese, this potentially presents a major risk factor for severe Covid-19 infection and may have implications for policy.’ 

Professor Mark Hamer, a clinical professor and honorary consultant in Sport and Exercise Medicine, led the research. 

He and colleagues, including from universities of Southampton and Edinburgh, drew on data from the UK Biobank study.

It collected data on 334,329 people from England with an average age of 56 between 2006 and 2010, asking them about their health and lifestyle habits. 

The team compared the data in relation to cases of coronavirus hospital admissions recorded by Public Health England from March 16 up to April 26.

During this period, testing was restricted to those with symptoms in hospital, therefore the study represents severe Covid-19. 

Around 0.2 per cent, or 640 people, from the large population sample ended up in hospital after contracting the virus.

Through their adjusted models, researchers found ‘there was a linear increase in the risk of Covid-19 with increasing BMI’.

It became evident from modestly elevated weight, as those with a BMI over 25 had a 40 per cent higher risk of hospitalisation after taking into account age and sex – two independent risk factors for Covid-19.

For those in the obese category (BMI 30 to 35), the risk was 70 per cent higher.

And those in the severe obese category (BMI more than 35), the odds of hospitalisation more than doubled.

Underweight people, with a BMI of below 18.5, had a six per cent increased risk of severe Covid-19 compared to those of a healthy weight. 

The risks were still there, but not as high, after taking into account a number of risk factors from smoking, alcohol consumption, education, ethnicity, diabetes, high blood pressure and cholesterol levels.  

BMI measures a person’s height and weight to work out if their weight is healthy. 

For most adults, an ideal BMI is in the 18.5 to 24.9 range. But medical conditions can arise at a BMI lower than 25 for people of certain ethnicities. 

BMI is only one way of calculating if a person is overweight. Therefore the research also used waist-hip ratio (WHR), a proxy measure for fat on the abdomen. 

A waist-to-hip ratio, calculated by the circumference of a person’s waist divided by circumference at their widest hip point, of more than 0.9 in men and 0.8 in women was used to denote central obesity around the middle. 

A similar pattern between WHR and risk of Covid-19 hospitalisation was discovered. But the findings were not detailed clearly in the paper, published by the Proceedings of the National Academy of Sciences of the United States of America journal. 

The findings chime with Glasgow University, which also studied 428,000 people part of the UK Biobank, of whom 340 had received a positive Covid-19 test result in hospital.

They found that underweight people had a five per cent greater risk of being admitted to hospital with coronavirus, compared to healthy people. Overweight people had a 62 per cent greater risk than healthy people, while the risk was 129 per cent higher for obese people.

The findings chime with Glasgow University, which found underweight people had a five per cent greater risk of being admitted to hospital with coronavirus, compared to healthy people. Overweight people had a 62 per cent greater risk than healthy people, while the risk was 129 per cent higher for obese people


Studies have shown obese people are more likely to suffer serious complications or die from infections, such as the flu. 

Doctors say the immune systems of fat people 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. 

Dr Dyan Sellayah, a lecturer in cellular and organismal metabolism, University of Reading, said 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.’ 

Obese people might eat a diet with very little fiber and antioxidants – which keep the immune system healthy – such as fruit and vegetables.  

Most patients with a BMI of over 40 suffer from breathing problems that range from simple shortness of breath to a potentially life-threatening condition known as obesity hypoventilation syndrome (OHS).

Public Health England (PHE) has previously suggested that obesity leads to fatty tissue around the upper airway, and a heavy chest can directly reduce lung function. 

Excess weight may make it more difficult for the diaphragm and lungs to expand and inhale oxygen. Starved of oxygen, organs will begin to fail.  

But other experts have disagreed with this theory, saying severely ill Covid-19 patients end up on ventilators anyway and still end up with worse outcomes. 

There are several other factors that may increase an obese person’s chance of falling seriously ill with coronavirus, including a lack of exercise.

Studies have shown that physical activity increases the numbers of certain immune cells that help to bolster immune activity.  

Clogged up arteries also make it hard for blood carrying immune cells to pass through and repair cells around the body.  

Obesity is tied with conditions such as type 2 diabetes, is more common among poor communities and some ethnic groups – all of which have been shown to raise the risk of severe Covid-19.

However, these cannot entirely explain the links between obesity and Covid-19, experts say, and it is its own independent risk factor. 

In further analyses, the scientists found that ‘impaired glucose and lipid metabolism’ – how the body use types of sugar and fat – may contribute to the link between obesity and severe Covid-19.

They showed that increases in BMI were linked with increases in cholesterol and  blood glucose (sugar) levels, called HbA1c.  

‘Impaired glucose regulation appears to be a plausible mechanism,’ the researchers said.

They added that the theory that extra fat compresses the chest is too simple to explain why obese people are more at risk of Covid-19.

Public Health England (PHE) has previously suggested that obesity leads to fatty tissue around the upper airway, and a heavy chest can directly reduce lung function.

However, a heavy chest is ‘irrelevant’ Professor Sir Stephen O’Rahilly, director of the MRC Metabolic Diseases Unit, Institute of Metabolic Science, University of Cambridge, argued.

He said: ‘Patients with Covid-19 who are on ventilators are usually mechanically ventilated with ease.

”Fat around the upper airway’ is obviously irrelevant to an intubated ventilated patient, yet obese people who are ventilated still have worse outcomes.’  

Obesity is also associated with low level inflammation, which could  exacerbate the inflammation that comes with infection, leading to more severe illness.  

PHE have also suggested excess fat is likely to weaken immune function.

The government agency published a report month – one of the most extensive reviews of the topic to date – but some experts said because it was done in haste, it was not entirely reliable.

One meta analysis found that being overweight or obese can dramatically increase the risk of hospitalisation and death from coronavirus.

Overweight people, defined as a body mass index of over 25, are more than three times as likely to die of Covid-19 than those of a healthy weight.

People who have extra weight are also at higher odds of needing ventilation when ill with Covid-19 by seven-fold. 

Experts behind the report said ‘every kilo’ people lost would reduce their risk of being admitted to hospital with the coronavirus.

It came as Boris Johnson finalised plans for his anti-obesity strategy following his near-fatal brush with the virus in April.

Under the plans, restaurant and takeaway chains will be forced to publish the calories in every meal they serve and similar labels will also have to be placed on bottles and cans of beer, wine and spirits sold in shops. 

A £10 million advertising campaign will also be launched to highlight the risks of excess weight and capitalise on fear of the virus.

Overweight people are more than three times as likely to die of Covid-19 than those of a healthy weight, a Public Health England report said in July. People who have extra weight are also twice as likely to get severe illness, and are at higher odds of needing ventilation by seven-fold

Mr Johnson said: ‘Losing weight is one of the ways you can reduce your risk from Covid. I’ve lost about a stone and a bit, primarily by eating less. If we lose weight, we’ll be better able not just to individually withstand coronavirus but we’ll do a great deal to protect the NHS.’ 

Professor Hamer and team said their findings in a large cohort of people are consistent with smaller studies, which have produced inconsistent results.

But they drew upon some limitations in the own study, including that the data collection on BMI and other lifestyle factors was a decade ago, so people may have lost weight since then.

However, in a subsample of almost 20,000 people, a repeat assessment around the year 2014 showed people’s weight had stayed the same.

The researchers said they did not undertake cohort-wide testing, and so the true prevalence of Covid-19 in the 300,000 people remains unknown.

‘By virtue of the fact that obese participants are likely to present with more risk factors, these patients may have been prioritised for testing,’ they said.  

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