Men with excessive fat around their abdomen, commonly known as a “beer belly,” are at an elevated risk for heart disease and Type 2 diabetes, and now researchers are adding osteoporosis to the list of potential hazards.
While obesity is associated with a host of other health problems – hypertension, high cholesterol, asthma, sleep apnea and joint diseases – it has been widely accepted that overweight men were at a lower risk for bone loss.
“Not true,” said Dr. Miriam Bredella, a radiologist at Massachusetts General Hospital and an associate professor of radiology at Harvard Medical School. “Everyone thinks of osteoporosis as a disease of women. Studies all focused on women, and men were always thought to be fine. We specifically wanted to look at young men.”
Bredella and her team of researchers evaluated 35 obese men with a mean age of 34 and a mean body-mass index, a measure of body fat, of 36.5.
The men were divided into two groups: one with mainly subcutaneous fat, which lies just beneath the skin and is spread all over the body, and the other with mostly visceral or intra-abdominal fat, located deep under the muscle tissue in the abdominal cavity.
Visceral fat, which is what causes a pot belly even in thin people, is far more menacing because the fat is packed in-between the inner organs and is strongly linked to heart disease. Genetics, a high-fat diet and a sedentary lifestyle all contribute to visceral fat.
“What surprised us most was that men with visceral fat had significantly weaker bones than [the subcutaneous fat] group. These are men with the same degree of obesity and who were about the same age,” Bredella said in a telephone interview.
For the study, she put the men through a computed tomography, or CT scan, of the abdomen and thigh to measure fat and muscle mass, as well as very high resolution CT of the forearm.
She assessed bone strength to predict fracture risk using a technique called finite element analysis, which is used in mechanical engineering to determine the strength of materials for the design of bridges and airplanes.
What she found was that the bones of the group with more visceral fat were nearly twice as weak as those with subcutaneous fat, or fat spread all over the body.
The results also showed that muscle mass was positively associated with bone strength.
She said the size of her study was limited by the sophistication and expense of the imaging tools that were used to predict risk. Since the results of this study, she has evaluated an additional 30 men in the same fashion, rendering the same results.
There appears to be two main reasons that visceral fat leads to osteoporosis, Bredella said. One is that all people with visceral fat secrete less human growth hormone, which plays an important role in maintaining healthy bones. The second reason is that visceral fat secretes certain molecules that cause inflammation, which in turn, weakens bones.
The secretion of these molecules and their effect on the body will be the focus of her future research.