More than one in ten infection-related deaths among adults worldwide may be linked to obesity, according to a new analysis published in The Lancet.
The research, conducted by a team led by University of Helsinki researchers in Finland, analyzed data from over 540,000 individuals participating in cohort studies in Finland and the United Kingdom. Researchers used national hospitalization and death registries from 2018, 2021 and 2023 to determine that obesity is associated with a 70% higher risk of hospitalization or death from infection.
The Finnish cohorts included 67,766 adults with an average age of 42.1 years, 73.1% of whom were women. The UK Biobank group comprised 479,498 adults with an average age of 57 years, and 54.4% were women. Obesity was categorized based on body mass index (BMI): class 1 (BMI 30.0 to 34.9 kg/m2), class 2 (BMI 35.0 to 39.9 kg/m2), and class 3 (BMI 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 study authors noted. Their analysis examined the relationship between obesity and the incidence, hospitalizations, and mortality associated with 925 bacterial, viral, parasitic, and fungal infectious diseases, estimating the global and regional impact of this preventable risk factor.
9% of Infection-Related Deaths Attributed to Obesity
During the follow-up period, 8,230 new-onset infections were documented in the Finnish cohorts and 81,945 in the UK Biobank. Compared to individuals with a healthy weight, those with class 3 obesity were more than three times as likely to be hospitalized for infection (2.75 times more likely in the Finnish cohorts, 3.07 times more likely in the UK Biobank), to die from infection (3.06 times more likely in the Finnish cohorts, 3.54 times more likely in the UK Biobank), or to experience either hospitalization or death (2.69 times more likely in the Finnish cohorts, 3.07 times more likely in the UK Biobank).
The overall hazard ratio for severe infection – defined as either fatal or non-fatal – was 1.7 for people with any class of obesity, when compared to those with a healthy weight. This association remained consistent across different measures of obesity (BMI, waist circumference, and waist-to-height ratio), demographic groups, clinical subgroups, and a wide range of infections, including both acute and long-term, bacterial and viral, and parasitic and fungal types.
Applying these risk estimates to global disease burden data, the researchers estimated that obesity accounted for 8.6% of infection-related deaths in 2018, 15.0% in 2021, and 10.8% in 2023. The increase in 2021 likely reflects the impact of the COVID-19 pandemic, where obesity was a known risk factor for severe outcomes.
The study found that individuals with obesity were at increased risk for many common infectious diseases, including influenza, COVID-19, pneumonia, gastroenteritis, urinary tract infections, and lower respiratory tract infections, compared to those with a healthy BMI.
Specifically, the risk of infection varied by type. Obesity was most strongly linked to skin and soft-tissue infections (hazard ratio of 2.8) and least associated with acute pharyngitis or tonsillitis (hazard ratio of 1.5). For COVID-19, the hazard ratio was 2.3. Notably, no significant association was observed between obesity and HIV or tuberculosis.
Up to 11% of Infection-Related Deaths Potentially Preventable
The population-attributable fraction – the proportion of infection-related deaths that could be prevented by eliminating obesity – was highest in North Africa and the Middle East, reaching 18.1% in 2018, 32.1% in 2021, and 22.5% in 2023. The lowest attributable fractions were observed in South Asia, at 3.2% in 2018, 5.9% in 2021, and 4.1% in 2023.
The researchers estimate that between 9% and 11% of infection-related deaths worldwide could be prevented by addressing obesity, a figure that rose to 15% during the peak of the COVID-19 pandemic. This underscores the significant public health impact of obesity beyond its well-established links to chronic diseases like diabetes and cardiovascular disease.
“Obesity is well known as a risk factor for metabolic syndrome, diabetes, cardiovascular disease, and many other chronic conditions,” said Professor Mika Kivimaki (UCL Faculty of Brain Sciences). “Here we have found robust evidence that obesity is also linked to worse outcomes from infectious diseases, as becoming very ill from an infection is markedly more common among people with obesity.”
These findings highlight the importance of preventative measures, such as access to affordable healthy food and opportunities for physical activity, to reduce the risk of severe infections and improve overall public health.
