UK-Finland study extends obesity health risks to include infectious diseases

Individuals defined as obese face a 70% higher risk of hospitalisation or death from an infection than those of a healthy weight, claim the findings from joint UK-Finnish research.

The work published in The Lancet linked obesity to increased risk from a range of infectious diseases, such as flu, Covid-19, stomach bugs and urinary tract infections, with the risk rising with increases in body mass index (BMI).

Lead author, professor Mika Kivimaki (UCL Faculty of Brain Sciences), noted that the condition had long since been established as a risk factor for metabolic syndrome, diabetes, cardiovascular disease and many 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,” he stated.

Data from over 540,000 participants in large cohort studies from the UK Biobank dataset and Finland was investigated. Those taking part had their BMI assessed initially and were then followed up for an average of 13-14 years.

Those with obesity, defined as a BMI of 30 and above, had a 70% higher risk of hospitalisation or death from any infectious disease in the study period compared to people with a ‘healthy’ BMI between 18.5 and 24.9.

People with a BMI of 40 or higher had three times the severe infection risk compared to people with a healthy weight. The link was consistent regardless of the measure of obesity used (BMI, waist circumference, or waist-to-height ratio) and for a wide range of infection types.

Data was included for 925 bacterial, viral, parasitic, and fungal infectious diseases, with the authors focussing additionally on 10 common infectious diseases in more detail.

Obese patients were more likely to be hospitalised or die than people with a healthy BMI when suffering from flu, Covid-19, pneumonia, gastroenteritis, urinary tract infections, and lower respiratory tract infections, they said.

However obese individuals appeared not to suffer increased risks in the case of severe HIV or tuberculosis.

Researchers said that the connection to severe infections could not explained by obesity-related chronic conditions or lifestyle factors such as physical activity.

They added that previous studies suggested that obesity may contribute to a general impairment of immune function, including immune dysregulation, chronic systemic inflammation, and metabolic disturbances.

Added Kivimaki: “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.”

The researchers also found evidence that losing weight could reduce the risk of severe infections as people with obesity who lost weight had a roughly 20% lower risk of severe infections.

First author, the University of Helsinki’s Dr Solja Nyberg  warned: “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.”

Employing infectious disease mortality data from the Global Burden of Diseases (GBD) Study, the study 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. In the UK specifically, the proportion was higher at one in six (17%), while it reached 26% in the US.

Co-author Dr Sara Ahmadi-Abhari (Imperial College London), who conducted the GBDanalyses, offered a caution, however.

“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,” she advised

This study was funded by Wellcome, Medical Research Council and the Research Council of Finland.