Being overweight may cause more hospital admissions than previously thought

The study used a genetic technique to identify the sole impact of body composition on hospital admissions.


Individuals with higher adiposity are more likely to visit hospitals than others. Establishing the causal impact of adiposity on hospital admissions is essential in understanding the impacts of being overweight on the health system.

A new study by the Bristol Medical School’s Population Health Sciences analyzes this relationship. Scientists wanted to seek the impact of excess body fat on the yearly hospital admission rate.

The study used UK Biobank data from over 300,000 adults aged 39–72, with over 550,000 in-patient hospital admissions in relation to three related exposures: BMI, Waist Hip Ratio (WHR), and WHR adjusted for BMI.

Using a method called Mendelian randomization, scientists compared the estimates from conventional epidemiological analyses to quantify how being overweight may be causally related to disease and mortality. The method uses genetic changes in the genome linked to body composition to estimate the causal effect of being overweight on a health outcome. At the same time, it removes the effects of other factors that may jointly influence body composition and hospital admission rates.

The study shows an association between a direct causal effect of higher BMI and WHR on higher yearly hospital admission rates. An adverse fat distribution in a specific area is crucial to this relation.

Overweight people were between 16 percent to 26 percent more likely to be admitted to hospital with each 0.09-unit higher waist-hip ratio than 8 percent to 16 percent with each 4.74kg/m2 higher BMI. 

Dea Hazewinkel, the study’s lead researcher from the University’s Bristol Medical School and Population Health Sciences Institute, said“We live in increasingly obesogenic environments with the World Health Organisation identifying 39 percent of men and 40 percent of women as being overweight, and 11 percent of men and 15 percent of women as obese worldwide. Finding causal effect estimates between fatty tissue and hospital admissions larger than those previously reported in existing studies emphasizes the necessity of exploring policies aimed at reducing obesity in the population.”

“The results also suggest 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.”

Journal Reference:

  1. Audinga-Dea Hazewinkel et al. Mendelian randomization analysis of the causal impact of body mass index and waist-hip ratio on rates of hospital admission. DOI: 10.1016/j.ehb.2021.101088
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