According to the World Health Organization, approximately one in eight people worldwide was living with obesity in 2022. Obesity is frequently associated with the development of non-communicable diseases, including cardiovascular disease and type 2 diabetes. Additionally, there is increasing evidence that obesity increases the risk of severe infection and mortality for some infectious diseases, such as Covid-19. However, there are limited studies examining obesity’s associations with a wide range of infectious diseases. In research published in February 2026 in The Lancet, Solja Nyberg and colleagues conducted a multicohort study using pooled data from two Finnish cohort studies and the UK Biobank to assess the association of adult obesity with risk of infection-related hospital admissions of 925 infectious diseases. Those with Class III obesity had a 2.75 times and 3.07 times increased risk of infection-related hospital admissions in the Finnish cohorts and UK Biobank, respectively.
The study utilised data from two Finnish cohort studies, the Finnish Public Sector study (FPS) and the Health and Social Support Study (HeSSup), and the UK Biobank. BMI measurements were taken at baseline during 2000–2002, 1998, and 2006–2010 in the FPS, HeSSup, and UK Biobank, respectively. Underweight participants (BMI <18.5kg/m²) and those with BMI values >70kg/m² were excluded. Those remaining were then classified into healthy weight (BMI 18.5–24.9kg/m²), overweight (BMI 25.0kg/m²–29.9kg/m²), and obese (BMI ≥30.0kg/m²) categories. Obesity was further categorized into classes I, II, and III (BMIs 30.0kg/m²–34.9kg/m², 35.0kg/m²–39.9kg/m², and ≥40.0kg/m², respectively).
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To assess for first record of incident hospital-treated infection, participants were followed up via national hospitalisation and mortality registries until 2016, 2012, and 2022 in the FPS, HeSSup, and UK Biobank, respectively. In total, 925 distinct infectious disease diagnoses were included. In the Finnish cohorts, 67,766 participants were included in the analysis, of whom 7,394 were obese. In UK Biobank, 479,498 participants were included, including 116,262 who were obese.
When comparing the risk of infection-related hospital admission, Class III obesity had an increased risk compared those of a healthy weight in both cohorts, with 2.75 times and 3.07 times the risk for those in the Finnish cohorts and UK Biobank, respectively. When combining the data of the Finnish and UK Biobank cohorts, those with obesity had a notable increased risk of severe bacterial and viral infection, with 1.7 times and 2 times increased risk, respectively.
This study by Nyberg and colleagues provides evidence that adult obesity, in particular class III obesity, increases the risk of hospitalisation and severe infection of communicable diseases. This highlights obese individuals as a vulnerable group to infectious diseases, which can help inform public health measures such as providing adequate weight-loss interventions and ensuring vaccine uptake against infectious diseases. GlobalData epidemiologists forecast that in the seven major markets (7MM: US, France, Germany, Italy, Spain, UK, and Japan), diagnosed prevalent cases of obesity in men and women ages five years and older will increase from 157.3 million cases in 2026 to 160.7 million cases in 2034.
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