Obesity Increases Risk of Serious Infections by 70%

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People living with obesity are at higher risk of hospitalisation and death from many common infections, according to a study which suggests that excessive weight may be more harmful than previously realised.

Being very overweight is linked with a 70 per cent higher risk of serious infection from diseases including flu, pneumonia, gastroenteritis and urinary and respiratory tract infections, according to a paper published in The Lancet on Monday.

The research suggests obesity, rates of which have more than doubled in the past three decades and are still rising, carries risks beyond diabetes, cardiovascular disease and other chronic conditions.

The connection with so many different infectious illnesses suggested “broad biological mechanisms” may be involved, said lead author Professor Mika Kivimäki, of the UCL Faculty of Brain Sciences in London. It was 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”.

The connection was not universal however: severely overweight people did not appear to face an increased risk of death or hospitalisation from HIV and TB, for example.

The findings, based on a study of 540,000 people in the UK and Finland, suggest obesity may have been a driving factor in just over 10 per cent of deaths from infectious diseases in 2023 globally.

The link was identified during the Covid-19 pandemic, prompting researchers to try to discover whether it also applied to other infectious diseases. They found that the likelihood of bad outcomes grew as body weight increased, with the most severely obese having three times the risk of people whose body mass index fell within the healthy range.

However, the researchers cautioned that the study relied on observational data “and cannot confirm causality of the associations”. Nor were the UK and Finnish participants representative of the general population.

They suggested the findings underlined the need for increased access to affordable healthy food and opportunities for physical activity.

Solja Nyberg of the University of Helsinki, another author on the study, said it was especially important for very overweight people to keep recommended vaccinations up to date. As obesity rates were expected to rise globally, “so will the number of deaths and hospitalisations from infectious diseases linked to obesity”, Nyberg added.

The study found significant variations between countries linked to the prevalence of obesity. In 2023, the US had the highest proportion of obesity-linked infectious disease deaths among high-income countries, with a quarter linked to the condition, while in the UK the figure was one in six. Among the countries analysed, Vietnam had the lowest proportion, with just 1.2 per cent of deaths.

Sara Ahmadi-Abhari of Imperial College London, who conducted the analyses of global data, said although estimates of the global impact gave a sense of how large the problem may be, they should be interpreted with caution as data on infection-related deaths and obesity were “not always accurate, particularly in low-resource countries”.