Observational study finds obesity associated with 70% increased risk of infection-related hospitalization — Evidence Review
Published in The Lancet, by researchers from University of Helsinki, UCL, Imperial College London
Researched by
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Table of Contents
People with obesity face a substantially higher risk of hospitalization or death from infectious diseases, according to a large-scale study published in the Lancet. The findings are broadly consistent with existing research, which also highlights increased infection risk and poorer outcomes among individuals with obesity.
- Multiple studies have reported that obesity is associated with higher rates of infection-related hospitalizations and more severe outcomes from diseases such as influenza, COVID-19, and various hospital-acquired infections 1 2 3 4 5 6.
- Prior research has identified both biological and clinical mechanisms—such as immune system impairment and chronic inflammation—that may explain the link between obesity and increased susceptibility to infections 1 6 9.
- Some studies note a nuanced picture, with obesity appearing to lower short-term mortality in specific settings like sepsis, suggesting the relationship between obesity and infection outcomes may vary by disease type and clinical context 7 8 9.
Study Overview and Key Findings
This research arrives at a critical time, as obesity rates are rising globally and infectious diseases remain a leading cause of morbidity and mortality. While previous studies have linked obesity to worse outcomes in specific infections like COVID-19, comprehensive evidence across a broad range of infectious diseases has been lacking. By analyzing data from over half a million individuals in Finland and the UK, this study provides robust estimates of the impact of obesity on infection-related hospitalizations and deaths, highlighting a growing public health concern as obesity prevalence increases.
| Property | Value |
|---|---|
| Organization | University of Helsinki, UCL, Imperial College London |
| Journal Name | The Lancet |
| Authors | Dr Solja Nyberg, Prof Mika Kivimäki, Dr Sara Ahmadi-Abhari |
| Population | Adults with obesity and healthy BMI |
| Sample Size | n=500,000 |
| Methods | Observational Study |
| Outcome | Risk of hospitalisation or death from infections |
| Results | Obesity linked to 70% higher risk of infection-related hospitalisation or death |
Literature Review: Related Studies
To place these findings in context, we searched the Consensus database, which covers over 200 million research papers, using the following queries:
- obesity infection hospitalization risk
- infection mortality obesity association
- hospitalization outcomes obesity chronic conditions
The table below summarizes key themes and findings from related studies:
| Topic | Key Findings |
|---|---|
| Does obesity increase the risk and severity of infectious diseases? | • Obesity is consistently linked to higher risk of infections, including respiratory, surgical-site, and nosocomial infections 2 3 5 6 9. • Obesity increases risk of hospitalization and more severe illness from infections such as COVID-19 and influenza 1 4 10 11. |
| What biological mechanisms underlie the link between obesity and infection outcomes? | • Obesity impairs immune response and promotes chronic inflammation, increasing susceptibility to infections 1 6 9. • Excess adiposity may also affect host defense through metabolic and endocrine dysregulation 1 6. |
| Are there exceptions or paradoxes in mortality and infection outcomes by BMI? | • Some evidence suggests obesity may lower short-term mortality in specific conditions like sepsis, despite higher infection rates ("obesity paradox") 7 8 9. • Underweight individuals also face increased infection risk and mortality 9. |
| How does obesity impact infection outcomes in specific populations and contexts? | • Severe obesity is linked to worse outcomes in hospitalized COVID-19 patients, especially among the elderly or those with comorbidities 4 10 11. • Childhood obesity may increase mortality risk in critically ill or hospitalized children 12. |
Does obesity increase the risk and severity of infectious diseases?
The evidence overwhelmingly supports the conclusion that obesity increases both the risk and severity of a wide range of infections. The current study's estimated 70% higher risk of hospitalization or death from infection among people with obesity aligns with previous research across various infectious diseases, from influenza to hospital-acquired infections.
- Multiple studies have documented increased infection rates and worse outcomes—such as longer hospital stays and higher mortality—among obese adults and children 2 3 4 6 9 12.
- Obesity is a recognized risk factor for respiratory infections (e.g., pneumonia, influenza), surgical-site infections, and nosocomial (hospital-acquired) infections 2 5 6 9.
- The association is especially pronounced in the context of COVID-19, where obesity independently raises the risk of severe illness, ICU admission, and death 1 4 10 11.
- Increased infection risk with obesity has been observed in both community and hospital settings, across diverse populations 3 5 12.
What biological mechanisms underlie the link between obesity and infection outcomes?
Several studies highlight biological mechanisms that may explain why obesity increases infection risk and severity. Chronic low-grade inflammation, impaired immune function, and metabolic abnormalities are frequently cited.
- Obesity alters immune cell function and increases levels of pro-inflammatory mediators, weakening the body's defense against pathogens 1 6.
- Adipose tissue acts as an endocrine organ, influencing metabolic and immune pathways that can increase susceptibility to infections 1 6 9.
- Insulin resistance and related metabolic dysfunctions may further impair immune response and recovery from infections 1 6.
- The relationship between nutrition, immune function, and infection risk is complex and may be modulated by both obesity and undernutrition 9.
Are there exceptions or paradoxes in mortality and infection outcomes by BMI?
While obesity is generally associated with increased infection risk and complications, some studies report lower short-term mortality in obese patients with certain critical illnesses, such as sepsis. This so-called "obesity paradox" suggests a nuanced relationship between BMI and infection outcomes.
- Large retrospective studies have observed reduced short-term mortality in obese patients with sepsis, compared to those of normal weight, despite higher overall infection rates 7 8 9.
- The paradox may be due to unmeasured confounders or differences in the metabolic and inflammatory response during acute illness 7 8.
- Both underweight and obese individuals appear to be at higher risk of infection, with a U-shaped relationship between BMI and infection risk and outcomes 9.
- The generalizability of the "obesity paradox" beyond specific settings (like sepsis) remains debated among researchers 7 8 9.
How does obesity impact infection outcomes in specific populations and contexts?
The impact of obesity on infection outcomes can vary by age, comorbidity, infection type, and healthcare context. Certain populations, such as the elderly, minorities, and children undergoing critical care, may experience amplified risks.
- In COVID-19, severe obesity is independently associated with ICU admission, mechanical ventilation, and death, particularly among older adults and those with comorbidities 4 10 11.
- Childhood obesity is linked to higher mortality in hospitalized children with critical illness, cancer, or after transplantation 12.
- The prevalence of obesity and associated risks can differ substantially across regions and demographic groups, influencing the overall burden of infection-related morbidity and mortality 10 12.
- Social and healthcare system factors, such as access to care and weight stigma, may also affect infection outcomes in people with obesity 8.
Future Research Questions
While this study strengthens the evidence linking obesity to increased infection risk and severity, important questions remain regarding causality, underlying mechanisms, and targeted interventions. Further research is needed to clarify these issues and inform public health strategies.
| Research Question | Relevance |
|---|---|
| What are the biological mechanisms linking obesity to increased infection risk? | Understanding the precise immune and metabolic pathways involved could inform targeted therapies and preventive strategies 1 6 9. |
| Does weight loss reduce the risk of severe infection in obese individuals? | Interventional studies are needed to determine if and how weight reduction alters infection susceptibility and outcomes 1. |
| Are there differences in infection risk and outcome among different types of infections in obese patients? | More granular data could help tailor prevention and treatment protocols for infections with distinct pathophysiological features 2 5 9. |
| How do socioeconomic factors and healthcare access influence infection outcomes in obese populations? | Exploring disparities in infection outcomes and healthcare utilization could guide policy interventions to reduce inequities 8 10 12. |
| What is the role of the 'obesity paradox' in infection-related mortality across different clinical contexts? | Further research may clarify under what circumstances, if any, obesity confers a survival advantage and the mechanisms behind this paradox 7 8 9. |