From flu to stomach bugs: study links obesity to more severe infections
Obesity may weaken the body’s defences against infection, strengthening the case for targeted vaccination policies.
- 11 February 2026
- 5 min read
- by Linda Geddes
At a glance
- We know obesity may impair they body’s ability to fight infections, but until now few studies have looked at how it influences the risk of becoming seriously ill across many different infectious diseases.
- A new study published inThe Lancet suggests that globally more than one in ten deaths from a wide range of infectious diseases could be linked to obesity, and that people with obesity are around 70% more likely to be hospitalised or die from an infection.
- The researchers say obesity should be treated as an important risk factor in efforts to prevent severe infections, including when designing vaccination strategies for high-risk groups.
Obesity may play a role in more than one in ten infection-related deaths worldwide, according to a major new study linking excess weight to more severe illness from a wide range of infectious diseases.
Researchers analysing health data from more than half a million adults in the UK and Finland found that people with obesity were about 70% more likely to be hospitalised or die due to an infection, with risks rising sharply at higher body weights.
Further modelling using global health data suggested the impact could be even greater in some regions, with obesity estimated to account for more than one in five infection-related deaths in parts of North Africa and the Middle East.
The researchers say obesity should receive greater attention in public health efforts to prevent severe infections, including being considered as a risk factor when planning vaccination strategies for high-risk groups.
Why did researchers investigate the link between obesity and infection?
While obesity is well established as a risk factor for diabetes, heart disease and some cancers, and there's growing evidence linking it to worse outcomes in certain infections such as flu and COVID-19, there was no large-scale study looking across the full spectrum of infectious diseases.
Dr Solja Nyberg at the University of Helsinki in Finland and colleagues wanted to know whether excess weight makes people generally more vulnerable to becoming seriously ill from different types of infection. They also wanted to understand the potential global impact, given that rates of obesity are increasing in many countries.
To investigate, the researchers analysed health data from more than 540,000 adults taking part in large, long-term studies in the UK and Finland.
Participants had their body mass index (BMI) recorded at the start and were then followed for over a decade using national hospital and death records.
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The team examined who was hospitalised or died due to 925 different bacterial, viral, fungal and parasitic infections, and compared outcomes across weight groups to see whether people with obesity were more likely to experience severe illness.
They then combined these risk estimates with global data on obesity prevalence and infectious disease deaths to model what proportion of infection-related deaths worldwide might be attributable to obesity.
How strong is the link between obesity and infection risk?
The research, published in The Lancet, found that obesity is linked to a much higher risk of severe infection across a wide range of diseases.
People with obesity were about 70% more likely to be hospitalised or die due to an infection than those of a healthy weight, with the risk rising sharply at higher body weights. Those with the most severe obesity had roughly three times the risk.
“Obesity is well known as a risk factor for metabolic syndrome, diabetes, cardiovascular disease and many other chronic conditions. Here we have found robust evidence that obesity is also linked to worse outcomes from infectious diseases, as becoming very ill from an infection is markedly more common among people with obesity,” said the study’s senior author, Prof Mika Kivimaki at University College London.
Higher risks were seen across many infections, including respiratory, urinary, gastrointestinal, skin and viral illnesses such as COVID-19, and were present even in people without other major obesity-related diseases. The researchers did not find clear evidence of increased risk for severe HIV or tuberculosis.
Using global data, the team estimated that in 2023 about 0.6 million of the world’s 5.4 million infection-related deaths – just over one in ten – could be linked to obesity.
The proportion was higher during the COVID-19 pandemic and lower before it.
There were also substantial regional differences: estimates were highest in North Africa and the Middle East, and lower in South Asia, where fewer people meet the BMI threshold for obesity and other risk factors likely play a larger role.
However, the authors cautioned that global estimates rely on modelling and data that may be less reliable in some low-resource settings.
How does obesity make infections more dangerous?
The researchers believe several overlapping biological mechanisms are likely to be involved.
Obesity is characterised by immune dysregulation, chronic low-grade inflammation and metabolic disturbances such as insulin resistance and high blood sugar – all of which can impair the ability of immune cells to fight infections and create an environment that helps some pathogens to thrive.
“Our findings suggest that obesity weakens the body’s defences against infections, resulting in more serious diseases. People may not get infected more easily, but recovery from infection is clearly harder,” Kivimaki said.
What do these findings mean for vaccines and public health?
With obesity rates rising worldwide, the researchers say its role in severe infections is likely to become a growing challenge.
Because of this, obesity should receive greater attention in infection prevention strategies, including stronger efforts to prevent obesity, better access to weight-loss support and clearer recognition of obesity when planning vaccination programmes for higher-risk groups.
“As obesity rates are expected to rise globally, so will the number of deaths and hospitalisations from infectious diseases linked to obesity,” said Nyberg.
“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.
“Furthermore, if someone has obesity, it is especially important to keep their recommended vaccinations up to date.”
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