Obesity is a shared risk factor for many common diseases, explains Mika Kivimäki, PhD. “Obesity has been linked to increased risk for numerous diseases,” Dr. Kivimäki says. “We wanted to know whether these diseases are distributed across all people with obesity, or whether they cluster in smaller groups of individuals with obesity-related multimorbidity.” Multimorbidity, he adds, is defined as the presence of two or more diseases.

For research published in The Lancet Diabetes & Endocrinology, Dr. Kivimäki and colleagues developed an observational study to examine the role obesity plays in the development of complex multimorbidity. “For example, one obese person has diabetes, another musculoskeletal problem, and a third respiratory problems, depending on their individual vulnerabilities,” Dr. Kivimäki says.

BMI Categorized from Obesity to Underweight

For the outcome-wide, observational study, the researchers cultivated pooled prospective data from two Finnish cohort studies comprising 114,657 individuals aged 16-78. The UK Biobank was used to draw a cohort of 499,357 adults aged 38-73, which served as replication in an independent population.

Participant BMI and clinical characteristics were assessed at baseline and were categorized as obesity, which was ≥30.0 kg/m2 or greater; overweight, which was 25.0-29.9 kg/m2; healthy weight, which was 18.5-24.9 kg/m2; and underweight, which was less than 18.0 kg/m2. These designations were then further categorized into class 1 (BMI, 30.0-34.9 kg/m2), class 2 (35.0- 39.0 kg/m2), and class 3 (≥40.0 kg/m2).

Using Cox proportional hazards regression in the cohorts drawn from the Finnish databases, the study team examined links between obesity and 78 health outcomes in separate models. Obesity disease associations were considered only if they yielded an HR of at least 1.50, were meaningful at a Bonferroni corrected α level, and had a
P value of less than 6.3×10-4.

Participants With Obesity Are at Higher Risk for Multimorbidity

Analysis of the data showed that participants with obesity were at a higher risk of developing both simple and complex multimorbidity when compared with participants with a healthy weight (Figure). Age was an additional risk factor. Participants with obesity who reached age 75 had an estimated occurrence of simple multimorbidity of 53.3% (95% CI, 50.1-56.3) and complex multimorbidity of 8.3% (95% CI, 6.0-10.4). Among participants with a healthy weight, these occurrences were less likely with simple multimorbidity occurrence of 8.3% (95% CI, 6.0-10.4) and complex multimorbidity of 1.0% (95% CI, 6.0-1.4).

Obesity before age 50 was noted as being more strongly related to the incidence of complex multimorbidity (HR, 22.11; 95% CI, 13.68- 35.74) than obesity at older age (HR, 7.90; 95% CI, 5.48-11.41; P=0.0091).

“We found that obesity exposes people to increasing burdens of heterogeneous multimorbidity’s, including cardiometabolic, digestive, respiratory, neurological, musculoskeletal, infectious, and malignant diseases,” Dr. Kivimäki says. “No specific combination of obesity-related diseases was particularly common. In contrast, the first four diseases formed as many as 140 different combinations. For this reason, we use the term ‘heterogeneous
multimorbidity.’”

These findings suggest that obesity is an important target for disease prevention, to avoid the burden of a multi-target regimen. “The creation of healthy living environments with less factors that predispose to obesity presents a parsimonious approach to reduce multimorbidity at the population level, while obesity treatments, such as lifestyle interventions, pharmacotherapy, and bariatric surgery could prevent multimorbidity among those who receive them,” the study authors wrote.