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Improved understanding of how body mass index (BMI) impacts a patient’s length of stay in hospital and likelihood of admission to intensive care can help the NHS ensure adequate resources are available to meet patient demand, according to a new study by researchers at Oxford Population Health’s Health Economics Research Centre. The study is published in The Lancet Diabetes & Endocrinology.

Excess weight is a known risk factor for severe disease after COVID-19 infection, but the effect of BMI on hospital resource use has not been fully quantified. This new study aimed to establish whether patients’ BMI influenced their length of stay in hospital, their likelihood of admission to intensive care, and the total cost of their hospital care.

Whilst people living with obesity* make up approximately 26% of the UK population, the researchers found that people with obesity accounted for 44% of hospital admissions for COVID-19 in the UK between 1 April 2020 and 31 December 2021. Patients with obesity were significantly more likely to be admitted to intensive care, and the costs of their hospitalisations were significantly higher.

The researchers analysed data from 57,415 adult patients in England who were admitted to hospital with COVID-19 between 1 April 2020 and 31 December 2021. They looked at how long the patients stayed in hospital, whether they needed to be transferred to an intensive care unit, and how long those patients stayed in intensive care. The costs of hospitalisation were estimated based on these factors. The researchers compared the resource use of patients living with obesity with a reference group who had a BMI of between 18.5 and 25kg/m2, defined by the NHS as the ‘healthy range’. The key findings were:

  • Patients with obesity typically had longer length of stays in hospital than the reference group, at an average of 9.22 days, compared with 8.82 days for the reference group;
  • Whilst accounting for differences in patients’ comorbidities, patients living with obesity were twice as likely to be admitted to intensive care when compared with the reference group;
  • The average of cost of being hospitalised with COVID-19 for patients with a BMI of 18.5-25kg/m2 was £19,877. Accounting for differences in patients’ comorbidities, on average patients with overweight but not obesity had £794 higher costs for each admission than patients at a healthy weight. Patients with obesity had on average £2,736 higher costs for each hospital stay;
  • COVID-19 hospitalisations were estimated to cost the NHS £13.7billion during the study period, with treatment of patients with overweight or obesity estimated to account for 78% (£10.7billion) of total hospital expenditure for COVID-19.

James Altunkaya, lead author and DPhil candidate at Oxford Population Health, said ‘Excess weight and its related conditions are a major driver of ill-health, and these conditions are having an increasing impact on many more individuals than ever before.

Delivering appropriate healthcare resources to areas with higher proportions of people living with obesity is an important component of addressing persistent health inequities seen in the UK.

Our findings support the case for further investment in prevention efforts to reduce the impact of obesity and its associated conditions on individuals, and on the healthcare system at large.’


*defined as having a BMI of more than 30kg/m2