New research shows Cushing’s adds hidden fat BMI may overlook
Detailed body scans reveal higher fat levels in children despite similar BMI
Children with Cushing’s disease tend to have more total body fat than other children their age, even when their body mass index (BMI) is the same, a new study suggests.
The study also found that detailed body-composition scans were better than BMI at predicting risks for issues such as diabetes and heart disease, “suggesting that measures of fat composition could be better targets for treatment outcomes in these patients,” the researchers wrote.
The study, “Body Composition and Fat Deposition in Children with Cushing Disease and Associations with Cardiometabolic Risk Factors,” was published in the Journal of Pediatrics.
Why BMI alone can miss key signs of Cushing’s disease
Weight gain and obesity are hallmark features of Cushing’s disease, a condition caused by pituitary tumors that lead to chronically high levels of the stress hormone cortisol.
Still, as many as one-third of children with Cushing’s disease have a BMI below the usual obesity range, despite having excess body fat. BMI is a measure of body fat using a ratio of weight to height.
Although BMI is widely used to screen for obesity, it often fails to show how much fat a child actually has or how that fat is distributed. As a result, BMI can underestimate or overestimate a child’s true fat levels, which matter when assessing the risk of problems like heart disease, stroke, fatty liver disease, and type 2 diabetes.
Researchers at the National Institutes of Health in Maryland suspected that children with Cushing’s disease have a different body-fat makeup than children with typical obesity, and that these differences may relate to cardiometabolic risks.
To test this, the team analyzed data from 23 children with active Cushing’s disease and 46 healthy peers matched for age, sex, and BMI.
How researchers compared body composition in children
All participants had body measurements, fasting blood tests, and whole-body dual-energy X-ray absorptiometry (DXA) — a low-dose X-ray scan that measures body composition, including fat mass, lean mass (total body weight minus fat mass), and bone mass.
Researchers found that children with Cushing’s disease had 8.1% more total body fat than matched controls. This statistically significant finding was true for both girls (47.8% vs. 40.0%) and boys (46.6% vs. 38.3%).
Their lean mass was 7.5% lower overall, and this difference was again significant in both girls (50.3% vs. 57.6%) and boys (51.7% vs. 59.4%).
Bone mass percentages were also lower in children with Cushing’s disease — 1.95% vs. 2.43% in girls and 1.75% vs. 2.39% in boys — a pattern that held true for both the trunk and limbs.
Despite these differences in overall fat, muscle, and bone, the pattern of where fat was stored — including in the trunk, limbs, and abdomen — was similar between the two groups.
We provide evidence that pediatric patients with CD have significantly different body composition compared with their BMI-similar peers without having an apparent different distribution of fat mass.
The researchers then looked at how body composition on DXA scans related to cardiometabolic risks, such as diabetes, liver problems, and high blood pressure.
For diabetes risk, elevated average blood sugar levels over the past three months were strongly linked to BMI and several measures of fat buildup. Insulin resistance also rose with higher BMI and more visceral (deep abdominal) fat.
Higher levels of alanine aminotransferase, a marker of liver irritation or damage, were associated with markers of fat distribution, but not BMI or total body fat percentage.
Total and LDL (“bad”) cholesterol did not correlate with body composition in children with Cushing’s, although these relationships did appear in the control group. The same pattern held for blood pressure, which showed stronger ties to BMI and fat deposition in controls than in patients.
“We provide evidence that pediatric patients with CD have significantly different body composition compared with their BMI-similar peers without having an apparent different distribution of fat mass,” the scientists concluded. “Additional studies are needed to explore the utility of markers of fat deposition and distribution in clinical management of these patient[s] and clinically significant outcomes.”
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