Are Obese Individuals at a higher risk of Infectious Diseases?

Authored by: Venkat Rao

Is it the case that overweight and obese people  are at a higher risk of infection and infection related outcomes compared to individuals with a healthy weight?  A recently published study seems to say so. We all have read about and seen on television numerous programs on obesity its adverse long-term consequences on health and wellness to the point we have become completely desensitized.  However, there is very little coverage on overweight/obesity with higher risk of catching infectious diseases and hospitalization.

A couple of studies, one from Finland and other from UK report a clear and close association between obesity and higher risk of infectious diseases hospitalization, even after adjusting for other risk factors such as type-2 diabetes, autoimmune disorders and lifestyle factors.  Hospitalization is indicative of the severity of the infectious diseases in the study population.

The Finnish study included over 67,000 adults 73% of whom were females in the 40–50-year age bracket with no recent history of infection and infection-related hospitalization at the study start baseline.  In the course of study follow-up, there were 8,230 cases of infection reported in the Finnish cohorts. 

The British investigation used a different study design based on the data extracted from the UK Biobank, one of the world’s most comprehensive databases on biological, health and lifestyle information on 500,000 participants.  The study involved a large sample set of nearly 480,000 adults of male and females in near equal proportion and with no reported history of infection-related hospitalization.  A time-series follow up on the UK Biobank participant data indicated 81,945 infections.  Analysis of risk of infectious disease incidence and hospitalization from two different investigations involving two distinct study models, showed a remarkably close patten linking obesity and higher risk of infections in both study populations. Both studies found the risk of infection-related hospitalization was three-times higher among morbidly obese (Class 3 obesity) individuals compared to healthy weight in both the Finnish and the British cohorts.

Class 3 obesity, formerly known as morbid obesity, is a chronic condition with body mass index

(BMI) at and above 40 kg/m². Morbid obesity is a well-established risk factor linked to severe weight-related health conditions and a higher risk of diabetes and heart diseases. Other serious systemic health conditions associated with Class 3 obesity include higher risk of certain types of pancreatic and colorectal cancers, kidney diseases, liver disease, depression and other mental health conditions are well reported in clinical and public health literature.  

Nonetheless, higher risk of infections diseases among obese individuals is relatively less reported in the published literature. According to the US Centers for Disease Prevention (CDC), United States has one of the highest levels of obesity with a prevalence. of 40.3 percent of the general population with both men (39.2%) and women (41.3%) in near equal proportion based on data collected between 2021 to 2023. 

The National Health and Nutrition Examination Survey (NANES), a component of CDC, collects and compiles extensive public health data nationwide on adult and children’s health and nutritional status has data collected over many decades. A wide prevalence of overweight/obese population in the US  across all socioeconomic levels, including young children and adolescent youth population.

According to CDC 1 in 5 children and adolescents are obese.  If we were to include overweight, the number swells to 1 in 3 children are either overweight or obese. This is a staggering public health statistic on the current health and wellness, placing enormous burden of expensive healthcare for patients and the healthcare system. Obesity rate among children is on the rise both in the US and globally.  According to a UNICEF 2025 children nutrition report, obesity was as high as 9.4%, the highest ever reported for children and adolescents in the 5 to 19 years age group.

An obvious next question would be, what is causing obese individuals more susceptible to infectious diseases and higher risk of hospitalization? Extensively documented evidence indicates obese individuals are susceptible to contract almost all categories of infectious diseases and are more likely to be hospitalized or die compared to others with normal body weight.  This includes an array of common public health related infections such as gastroenteritis, urinary tract infection, flu, COVID-19 and lower respiratory tract infections such as acute bronchitis and pneumonia.

In the case of bacterial infections, the overweight/obese individuals are at a higher risk, twice to three times, compared to others within the normal weight range. 

Obesity is well correlated with higher risk for skin and soft tissue infections even when taking into consideration the effect of type-2 diabetes and peripheral vascular disease. Increased risk of skin and soft tissue strongly correlated with overweight/obesity.  Higher body mass index appears to introduce an untoward risk level for skin abscesses, cysts, impetigo and infections of skin and the subcutaneous tissues. Impetigo is a highly contagious skin infection caused by Staphylococcus aureus mostly prevalent among younger adults.

In one of the detailed reviews on this topic, exploring the veracity of available evidence on obesity and higher risk of infectious disease, most published medical literature point to a higher incidence and outcome of certain types of community acquired infections among obese individuals.  Public health data suggests that overweight/obese individuals are more prone than people with normal weight to contract infections of various types that include post-operative infections and nosocomial, infections which are acquired from hospitals or other healthcare facilities  while receiving medical treatment for other health conditions. 

Although it is unclear how exactly overweight (higher body mass index) causes increased susceptibility to infectious diseases, severity of the disease requiring hospitalization, compromises in immune systems response through a variety of immune mediators is considered on of the most likely factors linked to obesity and higher risk of infectious diseases.

Obesity was a critical factor during the COVID-19 pandemic. Overweight/obese individuals demonstrated a higher susceptibility to contract COVID-19 and progress to sever levels of the disease.  COVID-19 global pandemic revealed an increased risk. of hospitalization, critical care admissions, and fatalities among obese individuals with a BMI above 40 kg/cm².  Increased risk was attributed primarily to pulmonary, endocrine and immune dysfunctions in overweight/obese individuals.

There isn’t a single, specific reason, or an underlying risk that places overweight/obese individuals at a higher risk compared to others.  It is not conclusive that excess body weight above a normal range is necessarily a warrant for serious adverse health consequences due to increased risk to infections.  Having said that, literature is replete with studies associating body weight with differential susceptibility, severity and response infectious diseases. 

A meta-analysis of 343 studies indicated individuals with BMI in the overweight/obese range tend to be more susceptible to infection, prone to disease progression to severe levels, and respond poorly to medical intervention.  Preventive measures, including vaccines and other medical countermeasures tend to be less effective in individuals with higher BMI.  Given  the growing size of  the overweight/obese population that include children and adolescents, the staggering additional medical interventional costs to an already overburdened healthcare system is a serious health security challenge of our time now and into the future.