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BMD:BMI ratio may better predict fracture risk in obesity
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BOSTON — Among adults with obesity, the lumbar spine ratio of bone mineral density to BMI may better predict fracture risk than BMD value alone, particularly when health care providers are unable to calculate trabecular bone score, according to study data presented at the American Association of Clinical Endocrinologists annual meeting.
“Obesity was thought to be protective against fracture for a long time, but recent evidence doesn’t prove this,” Mikiko Watanabe, MD, of the department of experimental medicine at Sapienza University of Rome, told Endocrine Today. “We work in an obesity center in Italy, and we found that these patients fracture far more often than what you would expect from their BMD values. We wanted to develop an index that could be easily obtained, that accounts for BMD and body mass.”
Watanabe and colleagues analyzed data from 2,225 white adults with overweight or obesity, assessing the correlation of BMD:BMI ratio with trabecular bone score (obtained via DXA scan) and that of lumbar spine BMD, trabecular bone score and BMD:BMI ratio with anthropometric parameters and cardiovascular risk factors (82% women; mean age, 45 years; mean BMI, 36.5 kg/m²).
Researchers observed a linear association between BMI and BMD, whereas trabecular bone score decreased with increasing BMI and BMD. Among 45.7% of patients with metabolic syndrome, lumbar spine BMD was comparable to metabolically healthy patients, according to researchers, but trabecular bone score and BMD:BMI ratio were both lower vs. healthy adults.
“Conversely, [trabecular bone score] appears to better reflect bone fragility in this category of patients, and it is inversely related to body mass, but its calculation may not be available to all,” the researchers wrote in an abstract presenting the findings.
“This index appears to reflect, much better than traditional indexes, bone fragility in obesity,” Watanabe said in an interview. “We only need their body mass and their DXA scan, so we think it is very promising and will better predict fracture risk.” – by Regina Schaffer
Reference:
Watanabe M, et al. Abstract #610. Presented at: AACE Annual Scientific and Clinical Congress; May 16-20, 2018; Boston.
Disclosure: Watanabe reports no relevant financial disclosures.
Perspective
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Steven Heymsfield, MD
The traditional view that people who are obese do not experience more osteoporotic fractures than people without obesity may not hold up very well.
The traditional thinking has been that, as a person becomes more obese, there is a strengthening of the bones, and as a result, people with obesity do not experience a loss of bone mineral mass and osteoporotic fractures. The marker of bone mineral mass is bone mineral density. If you have a DXA scanner, you can measure bone density, typically in the lumbar spine, and that helps predict risk. However, DXA is a two-dimensional method. To get density of the bone, one must correct for the amount of soft tissue over the bone. In people with obesity, these measurements are not extremely accurate because of the needed corrections. You’ll find that the density is pretty high, and there is a correlation with BMD and BMI — the two of them travel together.
What these authors have shown is that if you look at another measure — the architecture of the bone — you find that as people become more obese, the score goes down, not up, indicating that there is a problem with the architecture of the bone as opposed to its mass. By creating an index of BMD to BMI ratio, the authors found that that index, in turn, was a better predicter of bone fragility, which in turn is a better predicter of outcomes, such as osteoporotic fractures.
What this study does is draw attention to skeletal problems in obesity, beyond things like osteoarthritis of the knees, which we already know about. People with obesity can be predisposed to these fractures, and there may be better ways of quantifying that risk.
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