More than one in 10 infection-related adult deaths worldwide may be attributed to obesity, a team led by University of Helsinki researchers in Finland write in The Lancet.
The analysis of 67,766 adults in one of two cohort Finnish cohort studies, which was repeated with 479,498 adults from the UK Biobank, used national hospitalization and death registries in 2018, 2021, and 2023 to estimate that obesity confers a 70% higher risk of infection-related hospitalization or death.
The average age in the Finnish cohorts was 42.1 years, and 73.1% were women, while the average age and proportion of women were 57 years and 54.4%, respectively, in the UK Biobank group. Obesity was characterized by body mass index (BMI) as class 1 (30.0 to to 34.9 kilograms per square meter [kg/m2]), class 2 (35.0 to 39.9 kg/m2), or class 3 (40.0 kg/m2 or higher).
“Adult obesity has been linked to specific infections, but evidence across the full spectrum of infectious diseases remains scarce,” the authors noted. “In this multicohort study with impact modelling, we examined the association between this preventable risk factor and the incidence, hospitalisations, and mortality of 925 bacterial, viral, parasitic, and fungal infectious diseases, and estimated their global and regional attributable impact.”
9% of infection-related deaths due to obesity
During follow-up, 8,230 new-onset infections were documented in the Finnish cohorts and 81,945 in the UK Biobank. Compared with people of healthy weight, those with class 3 obesity were three times more likely to be hospitalized for infection (Finnish cohorts, 2.75 more likely; UK Biobank, 3.07), death (Finnish cohorts, 3.06; UK Biobank, 3.54), or either outcome (Finnish cohorts, 2.69; UK Biobank, 3.07).
The corresponding pooled hazard ratio (HR) for either fatal or non-fatal severe infection in people with any class of obesity was 1.7. This link held across different indicators of obesity (BMI, waist circumference, and waist-to-height ratio), demographic and clinical subgroups, and a broad range of infections (fatal and non-fatal, acute and long-term, bacterial and viral types and subtypes, and parasitic and fungal).
Applying these risk estimates to data on the global burden of disease, the researchers estimated the population-attributable proportions of infection-related deaths due to obesity at 8.6% in 2018, 15.0% in 2021, and 10.8% in 2023.
For most of the 925 diseases, including flu, COVID-19, pneumonia, gastroenteritis, urinary tract infection, and lower respiratory tract infections, obese people were more likely to be hospitalized or die than those with a healthy BMI.
By specific infection and infection group, obesity was associated with an increased risk for almost all infection types, with HRs ranging from 1.6 for parasitic, fungal, and chronic infections to 2.0 for viral infections.
For bacterial infections, HRs ranged from 1.7 for invasive infections to 2.1 for mycoplasma infections, with no links observed for mycobacterial or intracellular bacterial infections. HRs or viral infections ranged from 1.3 for herpesvirus infections to 2.3 for acute viral infections, while no association was seen for persistent viruses (except herpes).
Of 10 widely studied infectious diseases, obesity was most strongly tied to skin and soft-tissue infections (HR, 2.8) and was least associated with acute pharyngitis or tonsillitis (HR, 1.5). For COVID-19, the HR was 2.3. No links were seen for HIV (which made up 8.8% of all persistent non-herpes viral infections; HR, 0.9) or tuberculosis (accounting for 71.5% of all mycobacterial infections; HR, 0.7).
Up to 11% of infection-related deaths preventable
The highest population-attributable fraction for obesity-related infection deaths was seen in North Africa and the Middle East (18.1%) in 2018, 32.1% in 2021, and 22.5% in 2023. The lowest were seen in South Asia, at 3.2% in 2018, 5.9% in 2021, and 4.1% in 2023.
The researchers estimated that 9% to 11% of infection-related deaths worldwide could be prevented by eliminating obesity (rising to 15% during the COVID-19 pandemic).
