More Hospital Admissions Due to Being Overweight Than Thought

Dr Rob Hicks

January 17, 2022

It has long been recognised that those people who are overweight/obese attend hospital more frequently than those who maintain a healthy weight. Now researchers from Bristol Medical School’s Population Health Science Institute have suggested that being overweight may cause even more hospital admissions, and higher incidences of disease and mortality, than previously thought.

Body mass index (BMI) is a marker of overall body fat whilst waist-hip ratio (WHR) is a marker of regional adiposity, with both associated with an increased incidence of a number of diseases, including type 2 diabetes, hypertension, obstructive sleep apnoea, and certain cancers, as well as hospital admissions.

In their study, published in Economics and Human Biology , the researchers set out to determine the impact of excess body fat on yearly hospital admission rates in the UK. To do this they analysed data on BMI and WHR from the UK Biobank for 310,471 participants aged 39-72 (average age of 57.4 years), of whom 53.66% were female. Linked to this data were over 550,000 in-patient hospital admissions, and the average follow-up time was 6.05 years.

A Striking Discovery

The researchers employed Mendelian randomisation, which allowed them to quantify how being overweight may be causally related to disease and mortality. The method “removes the effects of other factors that may jointly influence body composition and rates of hospital admission”, said the authors.

A direct causal effect of higher BMI and WHR on higher yearly hospital admission rates was identified, with estimates that were larger than those obtained from existing research.

They found that people were between 16% and 26% more likely to be admitted to hospital with each 0.09-unit higher waist-hip ratio compared with 8% to 16% more likely with each 4.74kg/m2 higher BMI.

A striking discovery was that the greater risk of hospital admission was “largely driven by an adverse fat distribution in a certain area (measured by waist-hip ratio) rather than overall BMI”, the authors commented.

Dea Hazewinkel, the study’s lead researcher from the Institute, said: "Finding causal effect estimates between fatty tissue and hospital admissions larger than those previously reported in existing studies emphasises the necessity of exploring policies aimed at reducing obesity in the population."

Adult Obesity in England

The Health Survey for England 2019 estimated that 28.0% of adults in England are obese and a further 36.2% are overweight. The survey found that men are more likely than women to be overweight or obese (68.2% of men, 60.4% of women). People aged 45-74 are most likely to be overweight or obese.

Last year in 2021, NHS Digital published figures reporting that there were more than one million admissions to NHS hospitals in 2019/2020 where obesity was a factor.

At the time NHS England medical director Professor Stephen Powis said that the "shocking figures" were "a growing sign of the nation’s obesity crisis, which is putting hundreds or thousands of people at greater risk of becoming severely ill".

The researchers highlighted that theirs was the first Mendelian randomisation study of adiposity on all-cause hospital admissions, concluding that adiposity has a causal effect on increased hospital admission risk, and that the effect of adiposity on hospital admissions is driven by detrimental fat distribution.

In conclusion Ms Hazewinkel suggested that the study results indicated that: "A preference should be given to waist-hip ratio as a measure of body fat over BMI, as this may be more important for predicting hospital admissions."

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