People living with obesity face a significantly increased risk of hospitalization or death from infectious diseases, according to new research published . The study, involving over 500,000 participants, suggests that obesity may have been a factor in as many as 600,000 of the 5.4 million deaths from infectious diseases globally each year.
The findings, published in The Lancet, reveal that individuals with obesity are 70% more likely to be hospitalized or die from an infection. This increased risk extends to a range of common illnesses, including flu, pneumonia, gastroenteritis, urinary tract infections, and, as previously observed, COVID-19. For those with severe, or morbid, obesity, the risk of hospitalization related to infection nearly triples.
A Broadened Understanding of Risk
While the link between obesity and severe COVID-19 outcomes was established during the pandemic, this study expands that understanding to demonstrate a broader vulnerability to infectious diseases generally. Researchers analyzed data from two cohorts: 67,766 adults from Finland and 479,498 adults from the UK Biobank. Over an average follow-up period of approximately 12 to 14 years, they found a consistent association between higher body mass index (BMI) and adverse outcomes from infection.
Specifically, individuals with a BMI of 35 to 39.9 kg/m2 had a two-fold increased risk of hospitalization or death due to infectious disease compared to those with a normal BMI (18.5 to 24.9 kg/m2). Those with a BMI of 40 kg/m2 or higher faced a three-fold increase in risk. The association remained consistent across different measures of obesity – BMI, waist circumference, and waist-to-height ratio – as well as across various demographic and clinical subgroups and a wide range of infections.
“Our conclusion that obesity is a risk factor for a wide range of infectious diseases suggests that general biological mechanisms may be at play,” explains Dr. Mika Kivimäki of University College London, the study’s senior author, in a statement. “It is plausible that obesity weakens the immune system’s ability to defend against infectious agents, leading to more severe illness.”
Global Impact and Regional Variations
Extrapolating these findings to a global scale, researchers estimate that obesity may have been linked to approximately 10.8% of all infectious disease deaths in 2023 – a rise from 8.6% in 2018 and 15% in 2021. The impact varies regionally, with estimates suggesting that obesity contributed to 15.9% of infectious disease deaths in France, 17.4% in the United Kingdom, 25.7% in the United States, 21.2% in Spain, 14.7% in Germany, 3.8% in India, 1.2% in Vietnam, and 9% in China.
Immune System and Potential Interventions
The study points to a potential weakening of the immune system as a key mechanism driving this increased risk. This hypothesis is supported, researchers note, by the observed benefits of weight loss interventions, such as those achieved with GLP-1 receptor agonists, which appear to reduce the risk of severe infection alongside other health improvements.
However, the study also identified exceptions. Obesity did not appear to increase the risk of infection with HIV or tuberculosis. The researchers emphasize that these findings are observational and require further investigation to establish definitive causal links.
“These estimates of impact give an idea of the scale of the problem, but they should be interpreted with caution,” cautions Dr. Sara Ahmadi-Abhari of Imperial College London, who led the analyses of data from the Global Burden of Disease study. “Data on deaths related to infections and obesity in the GBD are not always accurate, particularly in low-resource countries.”
The study underscores the urgent need for public health policies aimed at promoting healthy weight and supporting weight loss, including access to affordable healthy food and opportunities for physical activity. Researchers also emphasize the importance of vaccination for individuals with obesity, who are particularly vulnerable to severe complications from infectious diseases.
As obesity rates continue to rise globally, the number of severe infections linked to the condition is expected to increase in the coming decades. Addressing this growing public health challenge will require a multifaceted approach focused on prevention, early intervention, and improved access to care.
