People living with obesity are 70% more likely to be hospitalised by or die from an infection, with one in 10 infection-related deaths globally linked to the condition, research suggests.
Being an unhealthy weight significantly increases the risk of severe illness and death from most infectious diseases, including flu, pneumonia, gastroenteritis, urinary tract infections and Covid-19, according to a study of more than 500,000 people.
Obesity may already be a factor in as many as 600,000 of 5.4 million deaths (11%) from infectious diseases every year, researchers found.
The study’s first author, Dr Solja Nyberg, of the University of Helsinki, said the problem could worsen. “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.”
In the meantime, she added, it was “especially important” for those living with obesity to keep up to date with their vaccinations.
During the pandemic, people living with obesity had a higher risk of being hospitalised or dying from Covid-19. However, until now, there was a lack of evidence about whether this link existed for infectious diseases in general.
To fill that evidence gap, the study used data from 67,000 adults in two studies in Finland and 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 and were followed for an average of 13 to 14 years. The average age at the start of the study was 42 for the Finnish group and 57 in the UK cohort.
The study, published in the Lancet, found that people with obesity, defined as having a BMI of 30 or higher, had a 70% higher risk of hospital admission or death from any infectious disease compared with people with a healthy BMI between 18.5 and 24.9. The risk increased as body weight increased.
The study’s lead author, Prof Mika Kivimäki, of UCL, said: “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. That said, additional research is required to confirm the mechanisms underlying these associations.”
The chances of dying differed between countries. About one in six infectious disease deaths were linked to obesity in the UK and one in four in the US, the study found. Vietnam had the lowest proportion, with obesity linked to 1.2% of infection deaths.
There were limitations to the research – which was funded by Wellcome, the Medical Research Council and the Research Council of Finland – including that it relied on observational data and could not confirm causality.
The study’s co-author, Dr Sara Ahmadi-Abhari, of Imperial College London, said: “Estimates of the global impact give a sense of how large the problem may be, but they should be interpreted with caution.”
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