Study Links Obesity to Higher Risk of Severe Infections Worldwide

Adult obesity significantly increases the risk of hospitalization and death from a wide range of infectious diseases, according to a large international study that reframes excess weight as a critical factor not only in chronic illness but also in global infection outcomes.

Drawing on data from more than 540,000 adults in Finland and the United Kingdom, researchers found that obesity raises the risk of severe outcomes across 925 bacterial, viral, fungal, and parasitic infections and is linked to roughly one in 10 infection-related deaths worldwide, a proportion that rose sharply during the COVID-19 pandemic.

The findings add new weight to concerns long raised by public health experts about the systemic effects of obesity and suggest that prevention and treatment strategies could play a role in reducing the burden of infectious disease. By combining epidemiological analysis with global mortality modeling, the study positions obesity as a modifiable risk factor whose impact extends beyond non-communicable diseases and into the core of health system resilience.

The research was designed to address a long-standing evidence gap. While obesity has been associated with worse outcomes in specific infections, including COVID-19 and influenza, there had been no large-scale, systematic evaluation of its role across the full spectrum of severe infectious diseases. Using a prospective multicohort design, researchers followed adults from two Finnish population studies and the UK Biobank, excluding individuals with prior severe infections to strengthen the temporal relationship between body weight and subsequent outcomes.

Obesity was measured using body mass index (BMI) alongside waist circumference and waist-to-height ratio to capture both overall and central adiposity. Over the follow-up period, incident infections were identified through national hospitalization and mortality registries and grouped into 22 disease categories. The results showed a clear dose-response relationship. Compared with individuals of healthy weight, those who were overweight faced a modestly higher risk of severe infection, while the risk rose sharply with increasing obesity class. Individuals with class III obesity experienced roughly three times the risk of infection-related hospitalization or death.

The association held after adjusting for socioeconomic status, education, smoking, alcohol use, and pre-existing conditions such as diabetes and cardiovascular disease. It was consistent across demographic subgroups and across different measures of adiposity, indicating that excess body fat itself contributes to vulnerability. Viral infections showed some of the strongest associations, including COVID-19 and influenza, while bacterial infections, sepsis, skin and soft tissue infections, and fungal and parasitic diseases were also linked to elevated risk.

To estimate the broader public health impact, the authors combined their findings with data from the Global Burden of Diseases Study. They estimated that obesity accounted for about 8.6% of infection-related deaths globally in 2018, rising to 15% in 2021 during the pandemic, before easing to roughly 10.8% in 2023. The burden varied widely by region, reflecting differences in obesity prevalence. North Africa and the Middle East showed the highest attributable fractions, while South Asia recorded the lowest. High-income regions, including North America and the European Union, fell in between, underscoring the relevance of the findings for developed economies.

Obesity is linked to immune dysregulation, chronic low-grade inflammation, and metabolic environments that can favor pathogen growth. Impaired T-cell and natural killer cell function, altered neutrophil activity, and reduced physical clearance of pathogens have all been documented. Together, these factors may limit the body’s ability to respond effectively to infections, particularly when combined with aging or chronic disease.

The study arrives amid broader debates over how best to address obesity at scale and how to balance fiscal, regulatory, and clinical approaches. In Mexico, where obesity prevalence is among the highest in the world, recent increases in health-related taxes have reignited discussion over their effectiveness. The National Alliance of Small Merchants has warned that sharp increases in excise taxes on sugary beverages and tobacco have driven price shocks across retail markets, contributing to inflation and pushing consumers toward cheaper brands or smaller package sizes. Industry data show early signs of reduced consumption in some categories, though analysts caution that demand for these products tends to be inelastic over time.

Public health specialists argue that taxes alone are unlikely to deliver sustained reductions in obesity without complementary measures. At the global level, the World Health Organization (WHO) warns that health taxes on sugary drinks and alcohol remain too low in most countries to significantly alter consumption patterns. The organization’s “3 by 35” initiative calls on governments to raise taxes on tobacco, alcohol and sugary beverages by at least 50% by 2035, framing fiscal policy as one tool among many rather than a standalone solution.

At the same time, pharmaceutical and clinical strategies are expanding rapidly. Demand for therapies targeting obesity and related metabolic conditions has grown as evidence mounts linking excess weight to a wide range of health outcomes, including infection risk. Recent licensing and distribution agreements in North America and Mexico underscore efforts to improve access to supervised hormone and metabolic therapies, while the global market for GLP-1–based obesity drugs has emerged as one of the fastest-growing segments in healthcare.

In Mexico, international partnerships aim to introduce new GLP-1 therapies for obesity and diabetes, reflecting rising demand for long-term metabolic management in a country where about one-third of adults live with obesity and diabetes affects more than 16% of the population. The WHO has formally endorsed GLP-1 therapies as part of comprehensive obesity management, while cautioning that access constraints could limit uptake to a small share of eligible patients by the end of the decade.

Parallel innovation is underway in cardiometabolic care, with pharmaceutical companies advancing oral therapies designed to improve adherence and expand access. Experimental cholesterol-lowering pills and oral GLP-1 receptor agonists have shown promising results in lowering LDL cholesterol, improving glycemic control, and reducing weight, though long-term outcomes data are still pending. Clinicians note that earlier intervention and simplified treatment regimens could reduce downstream complications, including infections, by improving overall metabolic health.

Prevention efforts, however, extend beyond clinical settings. The WHO recently issued its first global guideline on healthier school food policies, urging governments to adopt whole-school approaches that improve nutrition environments. Childhood obesity has surpassed undernutrition globally, and in Mexico, nearly one in five children and adolescents lives with obesity. Health experts warn that early-onset obesity is linked to earlier development of type 2 diabetes and cardiovascular disease, conditions that can compound infection risk later in life.

Mexico has also opened a public consultation to strengthen its front-of-package food labeling regulation, a policy widely credited with improving consumer awareness. Civil society groups argue that clearer, more visible warning labels could further reduce consumption of ultra-processed foods, which account for about 40% of daily calorie intake nationwide. Modeling studies suggest that maintaining and strengthening labeling policies could prevent more than a million obesity cases over time, though advocates emphasize that labeling must be paired with broader changes in food availability and affordability.

Dietary trends themselves remain contested. While restrictive approaches such as ketogenic diets have gained popularity for weight loss, recent long-term animal research has raised questions about potential metabolic tradeoffs, including impaired insulin secretion and lipid abnormalities. Nutrition experts in Mexico caution against unsupervised or extreme diets and stress the importance of sustainable, balanced approaches tailored to individual risk profiles.

Within this complex landscape, the new infection-risk study adds a unifying dimension by linking obesity to outcomes that extend beyond chronic disease management and into acute care and mortality. The authors note that weight loss from obesity to lower BMI categories was associated with reduced infection risk, though not fully to the level of individuals who had always maintained a healthy weight. This finding supports the value of both early prevention and effective treatment.

The researchers argue that obesity status should be considered in infection-prevention strategies, including vaccination prioritization and clinical risk assessment. They also point to emerging evidence from clinical trials showing that weight-loss medications can reduce all-cause mortality, in part by lowering infection-related deaths.

As obesity rates continue to rise globally, the study suggests that its contribution to infectious disease burden will grow unless prevention and treatment efforts accelerate. For policymakers, employers, and health systems, the findings reinforce the case for integrated strategies that link nutrition policy, clinical care, and access to effective therapies. In an era shaped by pandemics and aging populations, addressing obesity may prove critical not only for managing chronic illness but also for strengthening defenses against the next infectious threat.