Obesity linked to higher hospitalization and death risk from infections

Researchers estimate that, globally, over one in 10 deaths from various infectious diseases may be attributed to obesity. Their study suggests that people with obesity face a 70% higher risk of hospitalization or death from infection than individuals with a healthy weight. 

An analysis of data from over 540,000 people in the UK and Finland found associations with higher body mass index (BMI) and increased risk for diseases ranging from the flu and stomach bugs to urinary tract infections and COVID-19. 

The team categorized healthy weight as a BMI of 18.5–24.9 and obesity as a BMI of 30 or higher. People with a BMI of 40 or higher had three times the severe infection risk compared to individuals with a healthy weight.

“Obesity is well known as a risk factor for metabolic syndrome, diabetes, cardiovascular disease, and many other chronic conditions,” says the study’s lead author, Mika Kivimaki, professor at the University College London, UK.

“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.”

Moreover, the researchers reveal that the link to severe infections was not explained by obesity-related chronic conditions. They note that the association was consistent with people with obesity but without metabolic syndrome, diabetes, or heart disease, and the link was not explained by lifestyle factors like physical activity.

The new findings arrive amid growing consumer awareness of the broader health benefits of weight loss, driven in part by the increased use of GLP-1 and other weight-loss medications. US health and nutrition experts estimate that these drugs will have the greatest impact in 2026.

Global burden of disease

The team used infectious disease mortality data from the Global Burden of Disease study to model the impact of obesity on infectious disease deaths across countries worldwide, using the study’s risk estimates.

Weight loss may help reduce the risk, as people who lost weight had a 20% lower risk of developing severe infections than those who did not.They estimate the population-attributable fractions of obesity-related deaths from infectious diseases at 8.6% in 2018, 15% in 2021, and 10.8% in 2023. This would translate to 0.6 million out of 5.4 million infectious disease deaths globally in 2023.

The team estimates that in the UK, 17% of infection-related deaths can be attributed to obesity and 26% in the US.

“Estimates of the global impact give a sense of how large the problem may be, but they should be interpreted with caution,” comments co-author Dr. Sara Ahmadi-Abhari from Imperial College London, UK, who conducted these analyses.

“Data on infection-related deaths and obesity in the Global Burden of Diseases are not always accurate, particularly in low-resource countries.”

Infection risk

The Lancet study involved data from participants in the UK Biobank and a Finnish cohort study who had their BMI assessed at study entry. They were followed up for an average of 13–14 years.

The analysis included data on 925 bacterial, viral, parasitic, and fungal infectious diseases, while the researchers also zoomed in on 10 common infectious diseases.

People with obesity were more likely to be hospitalized or die than those with a healthy BMI for most of these diseases, including flu, COVID-19, pneumonia, gastroenteritis, urinary tract infections, and lower respiratory tract infections. However, the team found no association between obesity and the risk of HIV or tuberculosis.

The team estimates the population-attributable fractions of obesity-related deaths from infectious diseases at 8.6% in 2018, 15% in 2021, and 10.8% in 2023.The team notes that the link between obesity and severe infections was consistent across a wide range of infection types and valid regardless of the obesity measure used — BMI, waist circumference, or waist-to-height ratio. The association was also consistent across demographic and clinical subgroups.

Although the authors did not investigate the cause of this association in the observational study, they point to earlier studies suggesting that obesity contributes to a general impairment of immune function. This includes dysregulation, chronic systemic inflammation, and metabolic disturbances.

“Our findings suggest that obesity weakens the body’s defenses against infections, resulting in more serious diseases. People may not get infected more easily, but recovery from infection is clearly harder,” adds Kivimaki.

Weight-loss policies

The researchers note that losing weight can help reduce the risk of severe infections. Their analysis indicates that people with obesity who lost weight had a roughly 20% lower risk of severe infections than individuals who did not lose weight.

“As obesity rates are expected to rise globally, so will the number of deaths and hospitalizations from infectious diseases linked to obesity,” cautions the study’s first author, Dr. Solja Nyberg from the University of Helsinki, Finland.

“To reduce the risk of severe infections and 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.”

As the use of weight-loss medications and alternatives continues to grow, experts told Nutrition Insight about the long-term health effects of these drugs and their impact on nutrient deficiencies.