CT and Finite Element Analysis Reveal Men with Belly Fat at Risk for Osteoporosis

Imaging findings have revealed that visceral obesity is a risk factor for bone loss and decreased bone strength in men.

The study’s findings were presented November 28, 2012, at the annual meeting of the Radiological Society of North America (RSNA), held in Chicago (IL, USA). “It is important for men to be aware that excess belly fat is not only a risk factor for heart disease and diabetes, it is also a risk factor for bone loss,” said Miriam Bredella, MD, radiologist at Massachusetts General Hospital and associate professor of radiology at Harvard Medical School (Boston, MA, USA).

Obesity is associated with many health problems, including cardiovascular diseases, diabetes, high cholesterol, asthma, joint diseases, and sleep apnea. However, despite of all the health risks, it was typically accepted that men with increased body weight were at lower risk for bone loss. “Most studies on osteoporosis have focused on women. Men were thought to be relatively protected against bone loss, especially obese men,” Dr. Bredella said.

But not all body fat has similar health risks. Visceral (intraabdominal) fat is situated deep beneath the muscle tissue in the abdominal cavity and subcutaneous fat lies just below the skin. Diet, genetics, and exercise are all contributors to the level of visceral fat that is stored in the body. Excess visceral fat is believed to be especially dangerous, because in earlier research it has been associated with increased risk for heart disease.

The multicenter observational study called After the Osteoporotic Fractures in Men, designed to determine risk factors for osteoporosis, indicated that male obesity was associated with fracture risk, and the researchers set out to quantify belly fat and assess its impact on bone strength. Dr. Bredella and coworkers evaluated 35 obese men with a mean age of 34 and a mean body mass index (BMI) of 36.5. The men underwent computed tomography (CT) scanning of the abdomen and thigh to assess fat and muscle mass, as well as very high resolution CT of the forearm and a technique called finite element analysis (FEA), in order to evaluate bone strength and predict fracture risk.

“FEA is a technique that is frequently used in mechanical engineering to determine the strength of materials for the design of bridges or airplanes, among other things,” Dr. Bredella said. “FEA can determine where a structure will bend or break and the amount of force necessary to make the material break. We can now use FEA to determine the strength or force necessary to make a bone break.”

In the study, the FEA analysis revealed that men with higher visceral and total abdominal fat had lower failure load and stiffness, two measures of bone strength, compared to those with less visceral and abdominal fat. There was no association found between age or total BMI and bone mechanical characteristics.

“We were not surprised by our results that abdominal and visceral fat are detrimental to bone strength in obese men,” Dr. Bredella said. “We were, however, surprised that obese men with a lot of visceral fat had significantly decreased bone strength compared to obese men with low visceral fat but similar BMI.”

The study’s findings also revealed that muscle mass was positively associated with bone strength.

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