Examining the effects of obesity on the severity of COVID-19 symptoms
What were the objectives of the study?
Infection with the coronavirus, called SARS-CoV-2, does not affect everyone equally, with some prone to get more severe illness, called COVID-19, than others. Studies so far have shown that being overweight is associated with more severe disease, but it is unclear why. A person’s weight status is usually measured by body mass index, which is a measure of weight corrected for height.
The aim of this cohort study is to examine whether there is an association between body mass index and new cases, termed incidence, of COVID-19 and whether there is an increased incidence of severe infection requiring admission to hospital, admission to intensive care units, or resulting in death.
One explanation of why being overweight increases risk could be because being overweight increases the chance a person develops high blood pressure, type 2 diabetes, or heart disease. We will assess whether any increased risk from being overweight arises because these diseases increase the risk of severe COVID-19.
There is evidence that carrying excess fat around the waist increases the risk of heart disease compared with carrying excess fat around the hips and thighs. We will therefore also examine whether waist-hip ratio increases the risk of severe COVID-19 independently of body mass index.
Some people carry some of their body fat inside vital organs and it is thought that fat in the liver and pancreas is the main cause of type 2 diabetes. We will examine whether people with fat in the liver, called non-alcoholic fatty liver disease, and with raised blood glucose or type 2 diabetes are at particular risk over and above having a raised body mass index.
Losing weight reduces blood pressure, blood glucose, and reduces the risk of heart disease, but it is unclear whether it reduces the risk of severe COVID-19. We will compare the risk of severe disease in people who have been referred for weight management support by their GP compared with others with a similar starting body mass index.
How was the research done?
We will investigate the effect of body mass index (BMI), a commonly used measure of weight adjusted for height on the severity of COVID-19 disease in people who have tested positive for SARSs-CoV-2. We will also examine whether the associations are explained by diseases associated with obesity, and whether body fat distribution also explains the relationship.
Dr Nerys Astbury
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Generic ethics approval reference
Are all data accessed are in anonymised form?
Brief summary of the dataset to be released (including any sensitive data)
The cohort includes adults aged 18-99 years in 2020. Variables include BMI and those related to body weight and body fat distribution (waist circumference, hip circumference) from GP data and linked Public Health England COVID testing database (SGSS) as well as mortality and hospital data (HES admissions and ICU).
Implications and Impact
This research will contribute to the growing body of evidence which aims to identify characteristics that place individuals at greater risk of developing COVID-19 and those who may be more likely to experience severe symptoms once infected. The information generated will inform policy decisions related to sheltering or partial release from lockdown, as well as any future plans related to who should be prioritised when a vaccine eventually becomes available.
NIHR BRC Oxford
Public Benefit Statement
Dr Nerys Astbury
Professor Paul Aveyard
Professor Susan Jebb
Miss Min Gao
Dr Carmen Piernas
Associations between body-mass index and COVID-19 severity in 6·9 million people in England: a prospective, community-based, cohort study
Authors: Min Gao, Carmen Piernas, Nerys M Astbury, Julia Hippisley-Cox, Stephen O'Rahilly, Paul Aveyard, Susan A Jebb
Trusted Research Environment (TRE)