Obesity linked to one in 10 infection deaths globally

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Just over one in 10 deaths from a wide range of infectious diseases can be attributed to obesity worldwide, finds a major new study led by a University College London (UCL) researcher. People with obesity face a 70% higher risk of hospitalization or death from an infection than those of a healthy weight, according to the findings published in The Lancet.

Obesity can increase the risk posed by many different infectious diseases, from flu and COVID-19 to stomach bugs and urinary tract infections, and the researchers found that the higher the BMI, the greater the risk.

What the study set out to examine

The study’s lead author, Professor Mika Kivimaki (UCL Faculty of Brain Sciences), said, “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.”

The researchers studied data from over 540,000 people who participated in large cohort studies in the UK (the UK Biobank dataset) and Finland, 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 researchers found that people with obesity (defined as a BMI of 30 or higher) had a 70% higher risk of hospitalization or death from any infectious disease in the study period compared to people with a BMI between 18.5 to 24.9 (classified as a healthy weight).

The risk increased steadily as body weight increased. People with a BMI of 40 or higher had three times the severe infection risk compared to people with a healthy weight.

Broad impact across infection types

The link between obesity and severe infections was consistent regardless of the measure of obesity used (BMI, waist circumference, or waist-to-height ratio, where data were available) and for a wide range of infection types.

The study included data on 925 bacterial, viral, parasitic, and fungal infectious diseases, and the authors also honed in on 10 common infectious diseases in more 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 hospitalized or die than people with a healthy BMI. However, obesity did not appear to increase the risk of severe HIV or tuberculosis.

Possible mechanisms and lifestyle factors

The analysis found that the link to severe infections was not explained by obesity-related chronic conditions, as the association was consistent in people with obesity who did not have metabolic syndrome, diabetes, or heart disease, while the association was also not explained by lifestyle factors such as physical activity.

While the study did not investigate the causes of the association, the researchers say that previous studies have suggested that obesity contributes to a general impairment of immune function, including immune dysregulation, chronic systemic inflammation, and metabolic disturbances.

Professor Kivimaki said, “Our findings suggest that obesity weakens the body’s defenses against infections, resulting in more serious diseases. People may not get infected more easily, but recovery from infection is clearly harder.”

Benefits of weight loss and prevention

The researchers found evidence that losing weight can reduce the risk of severe infections, as people with obesity who lost weight had a roughly 20% lower risk of severe infections than those who remained obese.

First author Dr. Solja Nyberg (University of Helsinki) commented, “As obesity rates are expected to rise globally, so will the number of deaths and hospitalizations 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.”

Global burden and country estimates

The authors used infectious disease mortality data from the Global Burden of Diseases (GBD) Study to model the impact of obesity on infectious disease deaths for different countries, regions, and globally.

The analysis suggested 0.6 million out of 5.4 million (10.8% or one in 10) infectious diseases deaths globally were linked with obesity in 2023.

The researchers estimated that in the UK, one in six (17%) infection-related deaths can be attributable to obesity, and 26% in the US.

Co-author Dr. Sara Ahmadi-Abhari (Imperial College London), who conducted the Global Burden of Diseases (GBD) analyses, said, “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.”