More than one in 10 deaths from infectious diseases are associated with obesity, a global study led by UK researchers has found.
The analysis, published in The Lancet, found people with obesity – a body mass index (BMI) of 30 or higher – had a 70% higher risk of hospitalisation or death from an infection than those of a healthy weight with a BMI between 18.5 and 24.9.
Across a range of 925 bacterial, viral, parasitic and fungal infectious diseases including flu and Covid-19, stomach bugs and urinary tract infections, the data showed that the higher the BMI, the greater the risk of infection-related hospital admissions, death or either outcome.
The study analysed pooled data from more than 540,000 people who had taken part in two Finnish cohort studies or were included in repeated analyses in an independent population from the UK Biobank.
Participants were followed up through national hospitalisation and mortality registries for hospital admissions and deaths due to infectious diseases.
People with a BMI of 40 or higher had an approximately three-times higher risk of infection-related hospital admission (hazard ratio [HR] 2.75 in the Finnish cohorts; 3.07 in the UK Biobank, respectively), death (HR 3.06; 3.54), and either outcome (HR 2.69; 3.07).
The link between obesity and severe infections was found to be consistent regardless of whether researchers looked at BMI, waist circumference or waist-to-height ratio. However, obesity did not appear to increase the risk of severe HIV or tuberculosis.
The link to severe infections did not appear to be 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. Nor could the association be explained by differences in lifestyle factors such as physical activity.
But the data did show that people with obesity who lost weight had a roughly 20% lower risk of severe infections than those who remained obese.
Previous studies have suggested that obesity contributes to a general impairment of immune function, including immune dysregulation, chronic systemic inflammation and metabolic disturbances, the researchers noted.
Robust evidence linking obesity to worse infectious disease outcomes
Using infectious disease mortality data from the Global Burden of Diseases, the team estimated that 0.6 million out of 5.4 million (10.8%) infectious diseases deaths globally were linked with obesity in 2023.
In the UK, one in six (17%) infection-related deaths can be attributable to obesity, they added.
Study lead Professor Mika Kivimaki, chair of social epidemiology at University College London, 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.’
He added: ‘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.’
Last year, research showed that children born to mothers with a BMI of 35 or over are at an increased risk of being admitted to hospital with an infection.
A version of this article was originally published by our sister publication Pulse.