Healthcare (Commonwealth Union) – According to a study published in The Lancet, people who are obese are about 70% more likely to be hospitalized or die from an infection than people who are at a healthy weight.
The results show that being overweight makes you more likely to get a lot of different infections, such as the flu, Covid-19, gastrointestinal infections, and urinary tract infections.
The analysis showed a clear pattern: as body mass index (BMI) increases, so does the risk.
The study’s lead author, Professor Mika Kivimäki of the UCL Faculty of Brain Sciences, explained that while obesity is already recognised as a contributor to metabolic syndrome, diabetes, cardiovascular disease, and other long-term conditions, the research provides strong evidence that it also worsens outcomes from infectious diseases. Severe illness following infection, he noted, is significantly more frequent among people with obesity.
Researchers analysed health data from more than 540,000 participants enrolled in major cohort studies in the UK and Finland, including the UK Biobank. Participants’ BMI was measured at the start of the studies and they were tracked for an average of 13 to 14 years to assess links between obesity and serious infectious disease.
During the study period, individuals classified as obese — with a BMI of 30 or above — were found to have a 70% greater likelihood of hospitalisation or death from any infectious disease compared with those whose BMI fell within the healthy range of 18.5 to 24.9.
The danger rose progressively with increasing body weight. Individuals with a BMI of 40 or above faced roughly triple the risk of severe infection compared with those at a healthy weight.
The connection between obesity and serious infections remained stable no matter how obesity was measured — whether by BMI, waist size, or waist-to-height ratio — and applied across many different types of infections.
Researchers analysed information covering 925 infectious diseases caused by bacteria, viruses, parasites, and fungi, and examined 10 common infections in closer detail. For most of these — including influenza, Covid-19, pneumonia, gastroenteritis, urinary tract infections, and lower respiratory infections — people living with obesity were more likely to require hospital care or die than individuals with a healthy BMI. In contrast, obesity did not seem to raise the likelihood of severe HIV or tuberculosis.
The findings showed that the association with severe infections could not be fully attributed to obesity-related chronic illnesses. The pattern remained evident even among people with obesity who did not have metabolic syndrome, diabetes, or cardiovascular disease. It also could not be explained by lifestyle factors such as levels of physical activity.
Although the study did not directly explore the underlying causes, the researchers noted that earlier work suggests obesity may weaken immune performance overall, contributing to immune imbalance, persistent inflammation throughout the body, and metabolic disruption.
Professor Mika Kivimäki said the results indicate that obesity undermines the immune system, making infections more dangerous. While people with obesity may not catch infections more often, their bodies appear to struggle more to recover once they are ill.
The team also found signs that weight loss can lower the chances of serious infection. Individuals with obesity who reduced their weight showed about a 20% drop in the risk of severe infections compared with those whose weight stayed the same.
Lead author Dr Solja Nyberg of the University of Helsinki indicated that if global obesity levels continue to climb, deaths and hospital admissions tied to obesity-related infectious diseases are likely to increase as well.
“To reduce the risk of severe infections, as well as other health issues linked with obesity, there is an urgent need for policies that help people stay healthy and support weight loss, such as access to affordable healthy food and opportunities for physical activity. “
The researchers of the study made use of infectious disease mortality data that was obtained from the Global Burden of Diseases (GBD) research to model the effect of obesity on infectious disease deaths for various nations, regions across the world.
Co-author Dr Sara Ahmadi-Abhari of the Imperial College London, says “Estimates of the global impact give a sense of how large the problem may be, but they should be interpreted with caution. Data on infection-related deaths and obesity in the GBD are not always accurate, particularly in low-resource countries.”
