People living with obesity face a 70 percent higher risk of severe infectious diseases, and up to one in ten infection-related deaths globally could be linked to obesity, according to a new study published in The Lancet.
Researchers analysed health data from more than 67,000 adults in Finland and over 470,000 participants in the UK Biobank. Participants were grouped by body mass index (BMI) into healthy weight, overweight, and obese categories. Those classified as obese were further divided into three classes based on BMI, ranging from 30 to over 40 kg/m². Participants were followed for an average of 13 to 14 years to track hospitalisations and deaths from infections, including flu, COVID-19, pneumonia, and gastroenteritis.
The study found that people with obesity were 70 percent more likely to be hospitalised or die from any infectious disease compared with those of healthy weight. The risk increased steadily with higher BMI, with individuals in the most severe obesity category—BMI ≥40 kg/m²—having three times the risk of those with a healthy weight.
Mika Kivimäki, the study leader from University College London, said the findings suggest “broad biological mechanisms may be involved.” He noted that obesity could weaken the immune system’s ability to fight off infectious bacteria, viruses, parasites, and fungi, making infections more severe. Kivimäki stressed that additional research is needed to fully understand these mechanisms.
The study’s authors acknowledged limitations, including its observational design, which cannot establish direct cause-and-effect, and the reliance on BMI, which does not account for fat distribution or metabolic dysfunction.
Applying the study’s findings to global data, researchers estimate that 9 to 11 percent of infection-related deaths worldwide could potentially be prevented by eliminating obesity. The burden varies by country: in the United States, 25.7 percent of infection deaths are linked to obesity, while in Spain it is 21.2 percent, in the UK 17.4 percent, and in Germany 14.7 percent. India and China showed the lowest proportions, at 9 and 3.8 percent respectively.
Obesity rates are rising across Europe, with about 17 percent of adults classified as obese and 51 percent overweight, according to EU data. The World Health Organization (WHO) has described this trend as an “obesity epidemic.” Efforts to halt the rise in adult obesity by 2025 fell short, with rates increasing by 138 percent since 1975. New targets under WHO Europe’s 2022–2030 Non-Communicable Diseases Action Plan aim to reduce mean BMI by 30 percent by 2030, including measures to prevent child obesity.
Solja Nyberg, a co-author of the study from the University of Helsinki, said policies that support healthy lifestyles and weight loss are urgently needed. “As obesity rates are expected to rise globally, so will the number of deaths and hospitalisations from infectious diseases linked to obesity,” she said, highlighting the need for accessible healthy food and opportunities for physical activity.
