Obesity Raises Risk Of Severe Infection By 70%, Global Study Finds

A large international study has found that adults living with obesity face a sharply higher risk of being hospitalized or dying from common infectious diseases—a warning that carries particular resonance for countries such as India, where both obesity and infection burdens are rising.

Published in The Lancet, the analysis of more than 5.4 lakh participants from Finland and the United Kingdom reports that people with obesity are about 70% more likely to experience severe outcomes from infections compared with those in the healthy weight range.

For individuals with severe obesity, the risk may be as much as three times higher.

When the researchers applied these risk estimates to global mortality data, they calculated that obesity could have been linked to roughly one in ten infectious disease deaths worldwide in 2023. However, they cautioned that such modeling comes with uncertainties, particularly in countries where data quality is variable.

The elevated risk was observed across many everyday infections. These included influenza, COVID-19, pneumonia, gastroenteritis, urinary tract infections, and lower respiratory tract infections. Interestingly, the association was not evident for severe HIV or tuberculosis.

“Our findings suggest that people living with obesity are significantly more likely to become severely ill or to die from a wide range of infectious diseases,” said Solja Nyberg of the University of Helsinki, one of the authors of the study. With obesity rates expected to climb globally, she warned, the number of infection-related hospitalizations and deaths attributable to excess weight is also likely to rise.

Participants in the Finnish cohorts and the UK Biobank had their body mass index (BMI) recorded at enrollment and were followed for an average of 13 to 14 years. Obesity was defined as a BMI of 30 kg/m² or higher.

In the UK dataset, for instance, adults with a healthy BMI had about a 1.1% chance of a severe infection in a given year, compared with 1.8% among those with obesity. Risk rose progressively with increasing body weight.

Professor Mika Kivimäki of University College London, who led the research, said the pattern points to broader biological pathways. Excess body fat is known to influence immune responses and chronic inflammation, potentially weakening the body’s ability to fight invading pathogens.

There is also emerging evidence from clinical trials that substantial weight reduction, including through GLP-1 receptor agonist medicines, may lower the likelihood of severe infections alongside other benefits, though the mechanisms require further investigation.

Using estimates from the Global Burden of Disease study, the authors modeled how many infection deaths in individual countries might be linked to obesity.

High-income countries with a greater prevalence of obesity showed larger fractions. In the United States, about a quarter of infectious disease deaths were estimated to be associated with obesity, while in the United Kingdom, the figure was roughly one in six.

In India, where infectious diseases remain a major cause of mortality but obesity prevalence is lower than in many Western nations, the attributable fraction was estimated at 3.8%. In absolute numbers, that translated to about 46,000 of the 1.21 million infection-related deaths in 2023.

Public health experts say this dual burden—persistent communicable diseases combined with rapidly increasing overweight and obesity, especially in urban populations—makes the findings highly relevant.

India has witnessed a steady rise in obesity across age groups, driven by dietary shifts, reduced physical activity, and urban lifestyles. The National Family Health Survey has documented growing numbers of adults with high BMI, even as undernutrition remains a challenge in other segments.

The authors argued that strategies to reduce obesity could have spillover benefits beyond diabetes, heart disease, and cancer, extending into infectious disease outcomes as well.

They have called for policies that improve access to affordable healthy foods, create environments conducive to physical activity, and ensure that people with obesity remain up-to-date with recommended vaccinations.

At the same time, researchers have urged caution in interpreting the global extrapolations. The underlying data sources may not fully represent national populations, and observational studies cannot prove that obesity directly causes worse infection outcomes.

Sara Ahmadi-Abhari of Imperial College London, who worked on the modeling, noted that mortality and obesity data are particularly sparse in low-resource settings, which can affect accuracy.

Even with these caveats, clinicians said the message is clear: metabolic health and infectious disease preparedness are intertwined. As India strengthens surveillance for respiratory and emerging pathogens, attention to rising obesity could become an important part of resilience planning.