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The Lancet: People with obesity at 70% higher risk of serious infection with one in ten infectious disease deaths globally potentially linked to obesity, study suggests
- Study of over 540,000 people suggests people with obesity are 70% more likely to be hospitalised or die from an infectious disease; people with the most severe obesity face three times the risk.
- Applying these risk estimates to global data suggests obesity was linked to one in ten infection-related global deaths in 2023.However, authors highlight estimates of the global impact should be interpreted with caution.
- The proportion of infection-related deaths associated with obesity differed between countries, with roughly one in six deaths in the UK an done in four deaths in the US.
- Authors warn that given rising global obesity rates, the number of serious infections linked to obesity is likely to grow in the coming decades.
Obesity significantly increases the risk of hospitalisation and death from most infectious diseases, including flu, COVID-19, pneumonia, gastroenteritis, urinary tract infections and respiratory tract infections, suggests a study of 540,000 people published in The Lancet journal.
When these findings are extrapolated globally, they suggest obesity may have been a driving factor in 0.6 million out of 5.4 million deaths (10.8%) from infectious diseases in 2023.
Author Dr Solja Nyberg, University of Helsinki (Finland), says “Our findings suggests that people living with obesity are significantly more likely to become severely ill or to die from a wide range of infectious diseases. As obesity rates are expected to rise globally, so will the number of deaths and hospitalisations from infectious diseases linked to obesity.”
“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.”
During the COVID-19 pandemic, people with obesity had a higher risk of being hospitalised or dying with the SARS-CoV-2 infection, however there was a lack of evidence on if this link exists for infectious diseases in general.
To fill that evidence gap, this study used data from over 67,000 adults in two studies in Finland and over 470,000 adults in the UK Biobank dataset to look at the relationship between obesity and severe infectious disease.
Participants had their body mass index (BMI) assessed when they entered the studies and were then followed up for an average of 13-14 years. The average age at the start of the study was 42 years old for the Finish study and 57 years old for the Biobank cohort.
The study found that people with obesity, defined as BMI ≥30 kg/m², had a 70% higher risk of hospitalisation or death from any infectious disease compared to people with a BMI between 18.5 to 24.9.
For example, the UK Biobank adults with a BMI of 18.5 to 24.9 had a 1.1% risk of having a severe infection in a year whereas those with obesity had a 1.8% annual risk.
The risk increased steadily as body weight increased. People with the most severe obesity (BMI ≥40 kg/m²) had three times the risk of people with a healthy weight.
The authors also examined 10 common infectious diseases in detail. For most of these diseases, including flu, COVID-19, pneumonia, gastroenteritis, urinary tract infections, and lower respiratory tract infections, they found that people with obesity were more likely to be hospitalised or die than people with a healthy BMI. However, obesity did not appear to increase the risk of severe HIV or tuberculosis.
Professor Mika Kivimäki, University College London (UK), who led the study, says, "Our finding that obesity is a risk factor for a wide range of infectious diseases suggests that broad biological mechanisms may be involved. It is plausible that obesity weakens the immune system’s ability to defend against the infectious bacteria, viruses, parasites or fungi, therefore resulting in more serious diseases. Evidence from trials of GLP-1 weight-loss drugs fits with this, as reducing obesity also appears to lower the risk of severe infections, alongside many other health benefits [1]. That said, additional research is required to confirm the mechanisms underlying these associations.”
The authors also used infectious disease mortality data from the Global Burden of Diseases (GBD) Study [2] to model the impact of obesity on infectious disease deaths for different countries, regions and globally.
The GBD analysis suggested 0.6 million out of 5.4 million (10.8% or one in ten) infectious diseases deaths globally were linked with obesity in 2023.
National-level data revealed significant differences in the share of infectious disease deaths linked to obesity across countries (see Notes to Editors for a summary table and appendix 3 for full country data).
In 2023, the USA had the highest proportion among high income countries, with obesity linked to a quarter of infectious disease deaths (25.7%, 35,900/139,400). In the UK, obesity was linked to one in six infectious disease deaths (17.4%, 7,300/42,000).
In contrast, Vietnam had the lowest proportion of countries in the analysis, with obesity linked to 600 of 50,500 infectious disease deaths (1.2%).
The authors note several limitations including that the study relied on observational data and cannot confirm causality of the associations. Additionally, the Finland cohorts and UK Biobank are not representative of the general population so generalisability should be treated cautiously.
Dr Sara Ahmadi-Abhari, Imperial College London (UK), who conducted the GBD analyses, 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.”
Expert Reaction
These comments have been collated by the Science Media Centre to provide a variety of expert perspectives on this issue. Feel free to use these quotes in your stories. Views expressed are the personal opinions of the experts named. They do not represent the views of the SMC or any other organisation unless specifically stated.
Associate Professor Lesley Gray, Department of Primary Health Care, University of Otago Wellington
"Heightened risk from infectious diseases and large bodied people was reported for earlier pandemics, e.g. the 2009 H1N1 pandemic, although after adjusting for delayed access to antiviral treatment, there was no actual increased risk for large bodied people in that pandemic. One strategy is effective vaccination where available. For large bodied people, effective vaccination sometimes requires a longer needle to ensure the needle reaches the muscle (if the vaccination needs to be deposited into the muscle). However, in research I have conducted with colleagues globally and in New Zealand, we identified widespread under-utilisation of the correct needle length for large bodied people in COVID-19 vaccination.
"While it seems so simple for the authors to recommend in their conclusions that public health strategies aimed at preventing adiposity (body fatness) and evidence-based weight loss interventions should be implemented: we know that public health strategies over the last 30 or so years failed to produce sustained and effective prevention of body fat increase in populations. We also know that the body’s own regulation of body fat means that for large bodied people, most strategies are time limited and can lead to plateauing, and even higher levels of body fat once the intervention is stopped (including the new GLP-1 drugs that are being widely adopted).
"Importantly, many strategies adopted over that time increased weight stigma. Weight stigma itself is a chronic stressor and according to a recent clinical trial, weight stigma leads to an acute inflammatory body response in the person being subjected to the stigma.
"The landscape of inflammation and risk is complex and not easily treated, but important first steps involve the removal of barriers for timely early access to care, ensuring effective vaccination and treatments available for all body sizes, and importantly eradication of weight stigma in healthcare and across society."
Professor David Murdoch, Chief Scientist, New Zealand Institute for Public Health and Forensic Science (PHF Science)
"This very large study shows that adults with obesity are at substantially higher risk of becoming seriously ill or dying from infections. Importantly, the increased risk was seen across a wide range of infections, not just COVID-19, and rose steadily as body weight increased.
"Although this type of research cannot prove that obesity directly causes severe infections, the findings were consistent across two countries, different age groups, and many types of infection. They also fit well with what we already know about how obesity can affect the immune system, including reducing the body’s ability to fight infections and recover once someone becomes unwell.
"For New Zealand, these results are highly relevant. Obesity is common and increasing, and this study suggests its impact extends beyond long-term conditions such as diabetes and heart disease. It may also increase the likelihood that common infections become severe enough to require hospital care.
"The authors estimate that around one in ten infection-related deaths worldwide could be linked to obesity, with higher estimates during the COVID-19 pandemic. While these global figures are uncertain and depend on assumptions, they highlight the potential benefits of preventing and treating obesity.
"Overall, the study reinforces that supporting healthy weight through prevention and treatment could help reduce both chronic disease and the burden of serious infections on hospitals and health systems."
Professor Wayne Cutfield, Professor in Paediatric Endocrinology, Liggins Institute – University of Auckland
"It is well known that the consequences of obesity are far ranging and serious and include common non-communicable diseases such as diabetes mellitus, heart disease, stroke, liver disease, respiratory disease and cancer. In the USA, obesity is recognised by a number of medical organisations as a disease, and no longer just a risk factor for disease.
"In this large association study, the apparent risk of obesity extends to severe infections resulting in hospitalisation and or death. Much of what we understand about the risks of obesity are from association studies like this one, which do not prove cause and effect. It is not possible ethically or medically to conduct a clinical trial of serious infection risk in obese individuals.
"The prevalence of common diseases (diabetes mellitus, heart disease, hypertension) were notably lower than expected in the Finnish cohort of this study, raising the possibility of undiagnosed co-occurring conditions or obesity related diseases that may have also directly contributed to infection severity. Despite this caveat, the evidence provided by the authors suggests obesity probably influences infection severity in that: there is a “dose” related effect (greater obesity has an increased risk of severe infection), the findings are across 2 populations and there is a plausible biological explanation.
"These findings are timely in New Zealand as Pharmac considers whether Wegovy (semaglutide) should be funded for the treatment of obesity in adults and adolescents. The risk of severe infection adds to the long list of preventable or at least reducible obesity related diseases many New Zealanders face. Interestingly, during the Covid 19 epidemic, the SELECT trial of Wegovy for obese adults (with cardiovascular disease and without diabetes) led to fewer infection-related deaths."
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