MR Spectroscopy Shows Blood and Organ Fat May Increase Risk of Osteoporosis

A new imaging study has determined that excess liver and muscle fat also may be damaging to bone. The study’s findings were published online July 16, 2013, in the journal Radiology. “Obesity was once thought to be protective against bone loss,” said study lead author Miriam A. Bredella, MD, a radiologist from Massachusetts General Hospital (MGH) and associate professor of radiology at Harvard Medical School (both based in Boston, MA, USA). “We have found that this is not true.”

Whereas other research has investigated the link between visceral fat and bone mineral density, this study narrowed in on fat inside bone marrow, the spongy tissue inside the bones that generates 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 employed proton magnetic resonance spectroscopy (MRS), a technique that allows for precise measurement of fat, to study 106 men and women, ages 19 to 45 years, who were obese based on body mass index (BMI) measurements, but otherwise healthy. “MRS has no radiation, is quick to perform and can quantify the amount of fat within bone marrow, muscle and liver,” Dr. Bredella said.

The MRS imaging revealed that individuals with more liver and muscle fat had higher levels of fat in their bone marrow, independent of body mass index, age, and exercise status. High-density lipoprotein (HDL) cholesterol, the “beneficial kind of cholesterol that is associated with a lower risk of heart disease was inversely associated with bone marrow fat content. Higher levels of bone marrow fat put people at increased risk of fracture,” according to Dr. Bredella. “Bone marrow fat makes bones weak,” she said. “If you have a spine that’s filled with fat, it’s not going to be as strong.”

Triglycerides, the type of fat found in the blood, additionally had a positive relationship with bone marrow fat, possibly because they stimulate osteoclasts, a type of cell that breaks up bone tissue.

Additional studies are needed to better determine the processes behind this differentiation of stem cells. Dr. Bredella 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.

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