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Carrying excess weight increases the risk of becoming seriously unwell with COVID-19. New research found that excess weight increases the chance of admission to hospital or intensive care, or of dying. The under 40s and people of Black ethnicity were more affected by excess weight than others.

Early in the pandemic, small studies suggested that obesity increases the risk of having a worse outcome from COVID-19. Larger studies were needed to confirm this and to look at the risks to different groups of people. The new study therefore looked at the general UK population, not just people in hospital. It also considered all weights, and did not focus only on people with obesity.

The study, carried out during the first wave of the pandemic, included information on 6.9 million people. It found that severe outcomes from COVID-19 (admission to hospital, intensive care, or death) became more likely with increases in body mass index (BMI). This was true even within the healthy range. It was independent of other health conditions, including type 2 diabetes.

The research team looked at different groups within the population. They found that the risks of increased BMI were greater for people of Afro-Caribbean and Black African ethnicity than for White people. Risks were also greater for the under 40s than for older people. However, the extra risk with higher BMI was most serious for more people in their 40s and 50s, because this group generally has a higher risk of COVID-19 complications than younger people.

These findings emphasise the importance of investing in weight loss treatments and long-term strategies to prevent obesity and overweight. Such measures could reduce the severity of COVID-19 across the population.

Further information about obesity can be found on the NHS website.

What’s the issue?

Some people are more likely than others to become seriously ill with COVID-19. Characteristics that could increase risk (risk factors) include age, ethnicity and pre-existing health conditions. Excess weight is also thought to be a risk factor, and one that can be changed since people can lose weight.  

Early in the pandemic, researchers began to uncover evidence on the risk factors that mean some people are more likely to become severely ill or even to die. Small early studies on obesity compared outcomes among people with and without obesity who were in hospital with COVID-19. Researchers were unable to say for certain whether obesity or the infection increased the risk of intensive care or death.   

This study includes millions of people across the population who were not already ill with COVID-19. Importantly, the research looks at the impact of body weight, including within the healthy range, on the severity of illness. It also examines whether excess weight poses the same risk for all groups. Characteristics such as age, sex, ethnicity and long-term health conditions could make a difference. 

Body mass index (BMI) is calculated by dividing a person’s weight in kilograms by their height in metres squared. For most adults, a healthy BMI is between 18 - 25. Overweight is defined as a BMI of 25 - 30; obesity as a BMI of 30 or above. BMI is widely recorded in medical records, which allowed the research team to include data on millions of people.

What’s new?

This study used the anonymised medical records of 6,910,695 people (aged 20-99) who attended 1,500 GP practices across England. The data were linked to positive test results for COVID-19, and information on admission into hospital, intensive care or death.

In the three months to April 2020, 13,503 people were admitted to hospital, 1,601 to intensive care, and 5,479 died after a positive test.

The study found that people with a BMI of 23 had the lowest risk of admission to hospital, intensive care or death. As BMI increased, so did the risk of poorer COVID-19 outcomes.

Every unit increase in BMI: 

    • increased risk of hospital admission by 5% (above BMI of 23, in the healthy range)
    • increased risk of death by 4% (above BMI of 28, in the overweight range)
    • increased risk of intensive care by 10% (for any BMI). 

Being underweight also came with risks. Rates of hospital admission and death increased progressively as the BMI dropped below 20.

The researchers found that other factors influenced how much impact BMI had on outcomes from COVID-19.

    • Age: In people over 80, a higher BMI did not increase the risk of poorer outcomes. The risk of hospitalisation with higher BMI was greatest among the under 40s. But this group generally has a low risk of complications. The extra risk with increased BMI was most apparent for people in their 40s and 50s. 
    • Ethnicity: People of Afro-Caribbean or Black African ethnicity faced higher risks of poor outcomes with increasing BMI. The risk among people of Asian or Chinese ethnicity was similar to the risk among the White population.  

Previous research has suggested that being male increases the risk of poorer COVID-19 outcomes. However, this study found that sex had no effect on the association between BMI and severe COVID-19 outcomes. Similarly, having another health condition such as type 2 diabetes, high blood pressure or cardiovascular disease, did not add to the risks with increasing BMI.

Why is this important?

These findings confirm that any excess weight increases the risk of severe COVID-19 illness. Some groups are particularly affected. People in their 40s and 50s, and those of Black ethnicity, were most affected by a higher BMI. It is one of the most important risk factors that can be changed. 

A health survey in 2019 estimated that 28% of adults in England are obese and a further 36% are overweight.  This study found that most of the population has a BMI that puts them at increased risk of serious outcomes from COVID-19. Even small increases in BMI above 23, which is in the healthy range, increases the risk.

It has been known for decades that obesity reduces life expectancy and increases the chances of serious diseases such as cancer, heart disease and type 2 diabetes. The government’s new obesity plan, which launched in July 2020, stresses that supporting people to achieve and maintain a healthy weight could help reduce the risk of severe COVID-19.

What’s next?

The researchers plan to investigate whether the effectiveness of COVID-19 vaccines differs across the BMI range. If vaccines are less effective in people with obesity, who are most at risk of severe illness with COVID-19, they could be prioritised to receive booster vaccines.

More research is needed to understand the different mechanisms and biological pathways that explain the increased severity of COVID-19 in people who are overweight or living with obesity.

You may be interested to read

This NIHR Alert is based on: Gao M, and others. Associations between body-mass index and COVID-19 severity in 6.9 million people in England: a prospective, community-based cohort study. Lancet Diabetes & Endocrinology 2021;9:6

Information about the QResearch database, which was derived from anonymised patient records from GP practices

A policy paper from the Department of Health and Social Care: Tackling obesity: empowering adults and children to live healthier lives


Funding: The study was funded by NIHR Oxford Biomedical Research Centre and the NIHR Oxford Applied Research Collaboration. 

Conflicts of Interest: One author has received fees from a software company, unrelated to this work.

Disclaimer: NIHR Alerts are not a substitute for professional medical advice. They provide information about research which is funded or supported by the NIHR. Please note that views expressed in NIHR Alerts are those of the author(s) and reviewer(s) and not necessarily those of the NHS, the NIHR or the Department of Health and Social Care.

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