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People with a body mass index (BMI) over 30 are considered obese and particularly at risk for a wide range of diseases, including type 2 diabetes, cardiovascular disease, stroke, certain types of cancer, premature joint wear, and more. However, researchers at the Swedish institutions Sahlgrenska Academy, the University of Gothenburg and Skaraborg Hospital in Skövde have proven in a study that being overweight can actually save lives.

For this study, the scientists observed all 2,196 adult patients admitted to Skaraborg Hospital in Skövde for a suspected serious bacterial infection over a period of nine months. This showed that those with an elevated BMI also had significantly higher survival rates than normal-weight patients, both 28 days and one year after their hospitalization. For example, 26 percent of people in the normal-weight group had died within a year. By contrast, in the higher BMI groups, the figure was only between nine and 17 percent.

“Obesity survival paradox”

Previous, limited studies had already shown this “obesity-survival paradox,” which the new study was now able to confirm. “In the context of most other diseases, overweight and obesity are disadvantageous,” says the study’s primary author, Åsa Alsiö, Adjunct Senior Lecturer in Infectious Diseases at Sahlgrenska Academy and Senior Consultant in Infectious Diseases in Skövde. “This applies to several types of cancer, cardiovascular disease and, in particular, COVID-19, in which a higher BMI is associated with higher mortality. Paradoxically, it’s the other way round here.”

It is uncertain, however, how obesity may be beneficial for patients with a bacterial infection, she said. It’s unclear whether it’s related to functions in the immune system or how they are regulated. “More knowledge is needed about how being overweight affects the immune system. One patient category it could be studied in is individuals undergoing bariatric surgery. (stomach reduction, ed.).”

BMI as a key variable

Gunnar Jacobsson of the Sahlgrenska Academy and chief infectious disease physician at Skaraborg Hospital in Skövde hopes the findings may also help improve treatment of obese people with COVID-19. “The COVID-19 pandemic has highlighted vulnerable patient groups, and overweight people have been hit hard. Maybe experience and handling of care for patients with severe bacterial infections can be used to improve the prognosis of COVID-19 and overweight,” said the study’s lead author. “Globally, obesity is increasing at an alarming rate. More knowledge is needed to shed light on how body weight affects the body’s defenses against infection so that treatment can be individualized.”

But more population-level studies are needed to answer these questions, he said. This is the only way to examine how BMI affects treatment outcomes for various infectious diseases and what links might exist with immune system regulation, the researchers believe.

The results of the study, “Impact of obesity on outcome of severe bacterial infections,” conducted before the coronavirus pandemic, were published in the journal PLOS ONE.

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