People living with obesity are 70% more likely to develop severe infections requiring hospitalization or resulting in death, according to a new international study published this week. The analysis, which drew on health data from more than 540,000 adults in Finland and the United Kingdom, found a clear correlation between increasing body mass index (BMI) and the risk of severe illness from infections ranging from influenza to COVID-19.
Researchers analyzed long-term data from two Finnish health studies and the UK Biobank, following participants for an average of 13 years. A BMI of 30 or higher is defined as obesity and the study divided obesity into three levels, with the highest category including individuals with a BMI of 40 or above. Results indicated that those with the most severe obesity faced nearly three times the risk of severe infection compared to individuals with a healthy weight.
The link between obesity and infection severity was observed across many bacterial and viral diseases, with particularly strong associations for skin and viral infections, the study found. Scientists believe that obesity can impair the function of the immune system, reducing the body’s ability to effectively fight off harmful germs. Obesity is also linked to chronic inflammation and higher blood sugar levels, creating an environment conducive to bacterial and viral growth.
Using international health data, researchers estimated that around 600,000 of the 5.4 million infection-related deaths worldwide in 2023 may be linked to obesity – roughly one in ten such deaths. During the COVID-19 pandemic in 2021, this proportion rose to approximately 15%. The burden of infection deaths associated with obesity varies regionally, with North Africa and the Middle East showing some of the highest proportions, while South Asia recorded lower percentages, reflecting differing obesity rates across countries.
Changes in body weight over time also appear to play a role. Individuals who gained weight and transitioned into the obesity category experienced an increased risk of severe infection. Those who lost weight saw a modest reduction in risk, but it did not fully return to the level observed in individuals who had consistently maintained a healthy weight, highlighting the importance of early weight management.
In Finland, 24.5 percent of adults had a BMI of 30 or higher in 2024, according to data from the Finnish Institute for Health and Welfare (THL). What we have is an increase from 22.5 percent in 2020. The highest obesity rate in Finland was recorded in South Ostrobothnia, where just over 30 percent of the population was obese in 2024, an increase of nearly three percentage points since 2020.
The study authors emphasize that their findings are observational and cannot definitively prove that obesity directly causes severe infections. They also acknowledge that the study relies primarily on BMI, which does not provide detailed information about body fat distribution. However, the large number of participants and consistent results across different groups strengthen confidence in the findings.
Globally, obesity rates have nearly tripled since 1975, with approximately 13% of adults now obese and 39% overweight, according to the World Population Review. Pacific island nations currently have the highest obesity rates, with Nauru leading at 61% obesity.