A study by University of Oxford researchers has found that the risk of admission to hospital, admission to ICU or death from COVID-19 increases progressively above a ‘normal’ BMI of 23, even without other comorbidities.
The research team, who are supported by the NIHR Oxford Biomedical Research Centre (BRC), found that BMI is a greater risk factor for people aged 20 to 39 years than for older people, and for black people than for white people.
The study, published in The Lancet Diabetes and Endocrinology, looked at the anonymous health records from almost 7 million people in England aged between 20 and 99 years.
It found that the lowest risk was among those with a BMI of 23 kg/m2, at which point the risk increased linearly, around 5% higher risk of hospital admission, 10% higher risk of ICU admission, and 4% of death per unit increase in BMI.
Notably, the effect of excess weight on the risk of severe COVID was greatest in young people aged 20 to 39 years of age, and decreased after the age of 60. Excess weight had very little effect on the risk of severe COVID in people aged over 80 years.
The risks associated with higher BMI were greater for black people than white people. The increase in the risk of hospitalisation per BMI unit for black people was 7% compared with 4% for white people. And the increase in the risk of death for black people was 8% versus 4% for white people. There was no evidence that the risks for other ethnic groups differed from those of the white populations.
As the team say in the paper: “Excess weight is a modifiable risk factor and investment in the treatment of overweight and obesity and long-term preventive strategies could help reduce the severity of COVID-19 disease.”
The analysis took into account several factors that might influence risk, such as age, sex, ethnicity and existing health conditions, including type 2 diabetes. People with a BMI under 23, including those who are underweight (a BMI below 18.5) were also at risk of COVID-related hospital admission and death.
Read an article in The Conversation about this study.