A group of Boston researchers have found that obese people with higher levels of fat in their liver, muscle tissue and blood also have higher amounts of fat in their bone marrow, putting them at risk for osteoporosis and possibly, a fracture.
“Obesity was once thought to be protective against bone loss, ” said study lead author Miriam A. Bredella, M.D., a radiologist at Massachusetts General Hospital and associate professor of radiology at Harvard Medical School in Boston, in the July 16, 2013 news release. “We have found that this is not true.”
While other studies have examined the relationship between visceral fat and bone mineral density, this study looked at fat inside bone marrow, the spongy tissue inside the bones of the body that produces stem cells.
“In our study, we focused on bone marrow fat because that is where our stem cells can develop into osteoblasts—the cells responsible for bone formation—or fat cells, ” Dr. Bredella said. “We also wanted to look at the relationship between bone marrow fat and other fat components, such as those in the liver and muscle.”
Dr. Bredella and colleagues used proton magnetic resonance spectroscopy (MRS), a technique that allows for precise measurement of fat, to examine 106 men and women, ages 19 to 45 years, who were obese based on body mass index measurements, but otherwise healthy.
The MRS results showed that people with more liver and muscle fat had higher levels of fat in their bone marrow, independent of body mass index, age and exercise status. HDL cholesterol, the “good” type of cholesterol that is associated with a lower risk of heart disease, was inversely associated with bone marrow fat content.
The team also found that triglycerides also had a positive correlation with bone marrow fat, possibly because they stimulate osteoclasts, a type of cell that breaks up bone tissue. Dr. Bredella also noted that cell-signaling molecules called cytokines are known to promote the conversion of stem cells into fat. “Obesity can shift stem cell lineage, resulting in more bone marrow fat, ” she said.
