Johns Hopkins University-led research has found that obesity, particularly severe obesity, is strongly associated with the incidence of 16 common health outcomes, according to MedicalXpress. Associations remained consistent across sex and racial groups. Strong associations were observed for obstructive sleep apnea, type 2 diabetes, and metabolic dysfunction-associated steatotic liver disease.

Obesity is a risk factor for adverse health outcomes involving multiple organ systems. Prior studies have analyzed conditions individually, limiting understanding of obesity's total health burden. External validity has also been limited by underrepresentation of individuals with class III obesity and of diverse demographic groups.

Obesity is an increasingly prevalent condition in the United States, with current estimates suggesting that nearly half the adult population may meet the clinical criteria by 2030.

In the study, "Associations between Class I, II, or III Obesity and Health Outcomes," published in NEJM Evidence, researchers conducted a longitudinal cohort study to understand how different levels of obesity relate to a wide array of health conditions across a diverse U.S. population.

Data were analyzed from 270,657 participants enrolled in the All of Us research program, the largest cohort study in U.S. research history, launched by the National Institutes of Health in 2018.

Participants contributed electronic health records, physical measurements, and survey data. Body mass index (BMI) was calculated at enrollment and used to classify individuals as normal weight, overweight, or obese, with further stratification into obesity classes I, II, and III.

Sixteen pre-identified health conditions were evaluated: hypertension, type 2 diabetes, hyperlipidemia or dyslipidemia, heart failure, atrial fibrillation, atherosclerotic cardiovascular disease, chronic kidney disease, pulmonary embolism, deep vein thrombosis, gout, liver disease linked to metabolic dysfunction, biliary calculus, obstructive sleep apnea, asthma, gastroesophageal reflux disease, and osteoarthritis.

Cox proportional hazards models were used to estimate the risk of each condition by obesity class, adjusting for sex, age, race or ethnicity, income, and education. Researchers also calculated population-attributable fractions for each condition by obesity class.

Obesity was present in 42.4% of the study population, including 21.2% with class I obesity, 11.3% with class II, and 9.8% with class III. Compared to those with normal weight, individuals with obesity were more likely to be female, Black, have lower income and education levels, and have higher blood pressure and waist-to-hip ratios.

Prevalence and incidence rates increased progressively with higher obesity classes for all 16 health outcomes. Observed associations with class III obesity were strongest for obstructive sleep apnea (hazard ratio 10.94), type 2 diabetes mellitus (7.74), and metabolic dysfunction–associated liver disease (6.72). Weaker associations were found for asthma (2.14), osteoarthritis (2.06), and atherosclerotic cardiovascular disease (1.96).

Obesity was associated with elevated risk across all subgroups, with consistent patterns by sex and race. Population-attributable fractions showed that obesity explained 51.5% of obstructive sleep apnea cases and 36.3% of metabolic liver disease cases, and 14.0% of all osteoarthritis cases in the study population were estimated to be attributable to obesity.

Increased risk, particularly at higher severity levels, was associated with all 16 health outcomes studied. Risks rose in a stepwise manner across obesity classes, with the highest burden observed among individuals with class III obesity. Findings remained consistent across demographic subgroups and were supported by data from a large, diverse national cohort.

Associations between obesity and several conditions such as sleep apnea, type 2 diabetes, liver disease, and heart failure were strong and statistically robust. Population-attributable fractions indicated that a substantial proportion of these conditions may be preventable through effective obesity management.

Rising rates of severe obesity in the United States create urgency around intervention. Results from this study offer an updated estimate of obesity's total health burden and may support future public health strategies, policy actions, and clinical use of antiobesity therapies.