Obesity Linked to Increased Risk of Severe Infection, Hospitalization, and Death Across Disease Types

Obesity is associated with a significantly increased risk of severe infection, hospitalization, and mortality across a broad spectrum of infectious diseases, according to a large multicohort study published in The Lancet. The findings expand the clinical understanding of obesity beyond cardiometabolic disease, positioning it as a major and potentially modifiable risk factor for infectious disease outcomes.¹

The analysis, which included more than 540,000 adults from Finnish cohorts and the UK Biobank, found that individuals with obesity had an approximate 70% higher risk of hospitalization or death from infectious diseases compared with those of healthy weight. These results reiterate the need for more comprehensive risk assessment and prevention strategies in patients with obesity, particularly in pharmacy-led care settings.^1,2

Obesity Associated With Broad, Consistent Infection Risk

Unlike prior research focused on specific pathogens, the study evaluated 925 bacterial, viral, parasitic, and fungal infections, demonstrating a consistent association between obesity and severe outcomes across nearly all infection types.^1,2

The increased risk extended to common infections such as influenza, COVID-19, pneumonia, urinary tract infections, and gastrointestinal infections. Notably, individuals with class III obesity (body mass index [BMI]: ≥40) experienced up to a 3-fold increased risk of severe infection outcomes, including infection-related hospital admissions (Finnish cohorts: 2.75 [95% CI, 2.24-3.37]; UK Biobank: 3.07 [95% CI, 2.95-3.19]), death (Finnish cohorts: 3.06 [95% CI, 1.25-7.49]; UK Biobank: 3.54 [95% CI, 3.15-3.98]), or either outcome (Finnish cohorts: 2.96 [95% CI, 2.19-3.30]; UK Biobank: 3.07 [95% CI, 2.95-3.19]).^1,2

The association remained consistent regardless of how obesity was measured, including BMI, waist circumference, and waist-to-height ratio, and persisted across demographic and clinical subgroups. These findings suggest a broad biological mechanism linking excess adiposity to impaired host response to infection.¹

For pharmacists, this reinforces the importance of recognizing obesity as an independent risk factor when assessing patient vulnerability to infectious diseases, particularly during seasonal outbreaks or in immunization planning.¹

Substantial Global Burden Attributable to Obesity

Beyond individual risk, the study estimated a significant population-level impact. Approximately 9% to 11% of infection-related deaths globally may be attributable to obesity, with higher proportions observed during certain periods, such as the COVID-19 pandemic.^1,2

In 2023 alone, obesity was estimated to contribute to roughly 1 in 10 deaths from infectious diseases worldwide. The burden varied by region, reflecting differences in obesity prevalence and health system factors, but the overall trend highlights the growing intersection between obesity and infectious disease morbidity.¹

As global obesity rates continue to rise, investigators warn that the number of severe infections linked to excess weight is likely to increase in parallel. This evolving epidemiology has important implications for public health strategies and clinical practice.^1,2

Pharmacists, particularly those in community and ambulatory care settings, can play a key role in addressing this burden through preventive interventions, including vaccine advocacy, medication optimization, and referral for weight management services.

Potential Mechanisms and Clinical Implications

Although the study was observational, several mechanisms may explain the association between obesity and severe infection. Excess adiposity is known to contribute to chronic inflammation, impaired immune response, and reduced respiratory function, all of which may increase susceptibility to infection and worsen disease progression.²

Importantly, the study also found that changes in weight influenced infection risk. Individuals who reduced their weight from obese to lower BMI categories experienced fewer severe infections compared with those who remained obese, suggesting that risk may be at least partially reversible.²

From a clinical perspective, these findings emphasize the need to integrate weight management into infectious disease prevention strategies. Pharmacists can support this approach through counseling on lifestyle interventions, optimizing pharmacotherapy for obesity when appropriate, and addressing comorbidities that may compound infection risk.

Implications for Pharmacy Practice and Preventive Care

The findings have immediate relevance for pharmacy practice, particularly in the context of preventive care. Patients who have obesity may benefit from more proactive vaccination strategies, including immunization against influenza, COVID-19, pneumococcal disease, and other preventable infections.

Medication management is also critical, as pharmacists can identify drug-related contributors to weight gain, support adherence to antidiabetic and weight-loss therapies, and monitor for complications that may increase infection risk.

Additionally, pharmacists are well positioned to educate patients about the importance of early treatment for infections, as delayed care may lead to worse outcomes in higher-risk populations.

REFERENCES

1. Nyberg ST, Frank P, Ahmadi-Abhari S, et al. Adult obesity and risk of severe infections: a multicohort study with global burden estimates. Lancet. 2026;407(10532):951-962. doi:10.1016/S0140-6736(25)02474-2

2. Obesity may increase risk of severe infections. University of Helsinki. February 10, 2026. Accessed April 16, 2026. https://www.helsinki.fi/en/news/obesity/obesity-may-increase-risk-severe-infections