People living with obesity face a substantially higher risk of hospitalization and death from severe infections, according to a new, large-scale study published February 9 in The Lancet. Researchers found that individuals with obesity were 70% more likely to be hospitalized or die from infection compared to those without the condition. The study, encompassing data from over half a million people, likewise revealed that approximately one in ten infection-related deaths worldwide may be attributable to obesity.
This increased vulnerability extends beyond COVID-19, a connection highlighted during the pandemic when individuals with obesity experienced more severe outcomes. The new research demonstrates that this heightened risk applies across a broad spectrum of infections, including bacterial, viral, fungal, and parasitic illnesses, regardless of socioeconomic status or physical activity levels.
The comprehensive analysis drew data from three large cohorts: the UK Biobank, the Finnish Public Sector study, and the Health and Social Support study. Participants’ weight was assessed through self-reporting, body composition measurements, and waist circumference, offering a multifaceted approach to defining obesity. Researchers defined obesity as having a Body Mass Index (BMI) of 30 or higher, a waist circumference exceeding 40 inches for men or 35 inches for women, or a waist-to-height ratio of 0.6 or more.
“People with obesity may find it harder to fight off infections,” explained study senior author Mika Kivimäki, an epidemiologist at University College London. “Extra body fat can affect the immune system in several ways, including impairing lymphatic function, reducing lung function, and increasing long-term low-grade inflammation.” The lymphatic system plays a crucial role in immune function by maintaining fluid balance and transporting immune cells throughout the body.
The findings build upon earlier research indicating a link between obesity and infection susceptibility. A study published in August 2025 found that semaglutide, the active ingredient in medications like Ozempic and Wegovy, reduced the risk of severe infections by 10% Live Science. This suggests a potential pathway for mitigating infection risk through weight management.
Severity Increases with Degree of Obesity
The study revealed a clear dose-response relationship: the greater the degree of obesity, the higher the risk. Individuals with a BMI between 30 and 34.9 had a 50% increased risk of infection, hospitalization, or death. This risk doubled for those with a BMI of 35 to 39.9 and tripled for individuals with a BMI of 40 or above. Notably, changes in weight – both gain and loss – correlated with corresponding shifts in infection risk.
Complex Relationship Between Obesity and Immune Function
While the study establishes a strong association, researchers emphasize that it does not prove causation. However, experts suggest that the interplay between fat tissue and the immune system may be a key factor. Nikhil Dhurandhar, a professor of nutritional sciences at Texas Tech University who was not involved in the research, explained that fat cells can behave like immune cells and release pro-inflammatory substances. He also noted that obesity can disrupt immune function, potentially reducing the effectiveness of vaccinations.
Dhurandhar cautioned against viewing weight loss as a simple solution, acknowledging that maintaining weight loss is often challenging. “Obesity is a disease,” he stated. “It’s a chronic disease. It’s not a matter of willpower; it’s not a matter of discipline.”
Emerging Treatments and Future Research
The development of medications like semaglutide offers a potential avenue for weight management, but Kivimäki noted that the impact of these drugs on infection risk remains under investigation. He also pointed out that weight loss achieved through these medications can sometimes be accompanied by muscle loss, which could have negative consequences for the immune system. Muscle tissue provides glutamine, an amino acid essential for immune cell function, and produces interleukin-6, an anti-inflammatory compound.
“In our future research, we want to better understand why obesity raises the risk of severe infections,” Kivimäki said, “and, importantly, what can be done to reduce that risk.”
The findings underscore the importance of addressing obesity as a public health priority, not only for its well-established links to chronic diseases but also for its significant impact on susceptibility to infectious illnesses. Further research is needed to unravel the complex mechanisms underlying this relationship and to develop effective strategies for prevention and intervention.
This article is for informational purposes only and is not meant to offer medical advice.
Readers seeking support related to health concerns are encouraged to consult with a qualified healthcare professional.
