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.
