High BMI and poor physical fitness in adolescence linked to severe bacterial infections in adulthood

High BMI and poor physical fitness during later adolescence increase the risk of both contracting and dying from sepsis and other severe bacterial infections in adulthood, according to a study from the University of Gothenburg.

The study, published in the Journal of Internal Medicine, is based on national registry data covering almost one million men in Sweden. By linking data from the Swedish Military Conscription Register, the National Patient Register, and the National Cause of Death Register, the researchers were able to follow individuals for more than three decades.

When the men enlisted for military service, their BMI and physical fitness were measured. Based on these measurements, the participants were categorized into groups that were compared regarding their risk of later developing or dying from bacterial pneumonia, heart valve infection, or sepsis.

The analyses have been adjusted for factors such as muscle strength, socioeconomic status, and asthma, to provide the most accurate assessment possible of the link between BMI, fitness, and future infection risk.

Increased risk already at high normal weight

Josefina Robertson, Associate Professor of Infectious Diseases at the University of Gothenburg, infectious disease specialist at Sahlgrenska University Hospital, and the lead investigator of the study, explains:

It has long been known that high BMI and poor physical fitness in youth are risk factors for cardiovascular disease and cancer later in life. We have also shown this to be true for COVID-19. However, whether these factors are linked to the incidence of severe bacterial infections in adulthood has not been previously studied.”

Josefina Robertson, Associate Professor of Infectious Diseases, University of Gothenburg

In the current study, more than 44,000 cases of severe bacterial infections were identified during the follow-up period, with pneumonia being the most common, followed by sepsis. The results show a very strong association between both high BMI and poor physical fitness at conscription and the risk of later developing – and dying from – these infections. The risk was already elevated at high normal weight (BMI 22.5–25) and increased progressively with higher BMI and poorer fitness.

High BMI and low fitness levels were a particularly strong risk factor for sepsis. Among men with obesity (BMI 30 or more), the prevalence of sepsis was more than three times higher compared to those of low normal weight (BMI 18.5–19.9). In addition, the risk of dying from sepsis was more than four times greater in the highest BMI group.

Early interventions for better health

This is the first study to demonstrate a link between BMI and physical fitness in adolescence and the risk of developing bacterial infections later in life. Birger Sourander, doctoral student at the University of Gothenburg, resident physician at Sahlgrenska University Hospital, and first author of the study, emphasizes:

“Our findings are particularly relevant today, as overweight, obesity, and sedentary lifestyles are becoming ever more common, while antibiotic resistance continues to rise. The results therefore underline the importance of early interventions to promote a healthy weight and physical activity already in adolescence, for the future health of both the individual and society as a whole.”