Factors Associated with Low Bone Density in a Juvenile Mortality Sample
Authors: Hill Ethan C. , O'Donnell Lexi 
Published: May 2022

Here we examine relationships between chronic illness and low bone density (BD) in a juvenile mortality sample from New Mexico. Chronic illnesses are often found to be linked to low BD and growth stunting or arrest. Inflammation, either from disease or traumatic injury, has also been linked to bone loss. The purpose of this study is to test two hypotheses: 1) children who experience chronic illness will have lower bone density than those without; 2) children who experience growth stunting or growth arrest will have lower BD than those without. We include 433 individuals 6 months to 17 years old who underwent postmortem computed tomography (PMCT) between 2011 and 2019 at the University of New Mexico OMI.

Hounsfield units (HU), a proxy for trabecular BD, were obtained at three sites – lumbar spine, proximal femur, and proximal humerus – from PMCT scans using the freeware DICOM viewer Horos. HU in each region were age and sex standardized using this sample’s data (femur, humerus) or PRAMPTM data (lumbar). The resulting z‐scores were then used as the dependent variable in all analyses. We included age, sex, manner of death (MOD), growth arrest (Harris) lines, stunting, fatty liver, cardiomegaly, asthma, diabetes mellitus, cerebral palsy/seizure disorder, and osteopenia as independent variables in each model. We set the base level for MOD in each analysis as natural. Osteopenia was included as a control variable (as HU should be lower in individuals with osteopenia), along with age and sex. Results provided are coefficients for variables with p≤ 0.05. We used linear and logistic regression (odds ratios) to examine associations between being overweight or obese and fatty liver and cardiomegaly. All analyses were done using Stata 15.

We find that lumbar HU are significantly lower in individuals with fatty liver (‐0.58), diabetes (‐0.74), and cerebral palsy or epilepsy (‐0.72). Femoral HU are significantly lower in individuals with Harris lines on the tibia (‐0.28), diabetes mellitus (‐1.61), and cerebral palsy or epilepsy (‐0.59). Humeral HU are significantly lower in individuals with Harris lines on the tibia (‐0.32) and diabetes mellitus (‐0.72), and cerebral palsy or epilepsy (‐0.55). In each analysis, individuals with osteopenia have significantly lower HU than those without. In a subsequent series of regressions, we included overweight or obesity as independent variables and we do not find a link between those and decreased HU, but individuals who are overweight or obese have higher odds of having fatty liver, and those who are obese or morbidly obese have higher odds of having cardiomegaly.

Low BD in this sample is likely due to multiple, sometimes interrelated factors, including chronic illness and inflammation, inactivity, and perhaps social determinants of health (e.g., lack of access to healthy foods, healthcare). Obesity and nonalcoholic fatty liver disease are linked in children. While the natural history of pediatric nonalcoholic fatty liver disease is not known, there is some evidence that it may begin in utero. Individuals who are obese or overweight have increased odds of having fatty liver and cardiomegaly. While being obese or overweight is not directly related to decreased BD, the behaviors and social determinants of health that lead to obesity are likely related to low bone density as well.