Fatty Organs Linked to Osteoporosis
Scientists have linked higher levels of fat in liver, muscle tissue and blood to greater amounts of fat in bone marrow, which puts people at risk for osteoporosis.
"Obesity was once thought to be protective against bone loss," study lead author Dr. Miriam A. Bredella, M.D., a radiologist at Massachusetts General Hospital and associate professor of radiology at Harvard Medical School in Boston, said in a news release. "We have found that this is not true."
Researchers noted that while previous studies have looked at the link between visceral fat and bone mineral density, the recent 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," 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."
In the study, researchers used proton magnetic resonance spectroscopy (MRS), a technique that allows for precise measurement of fat, to examine 106 men and women who were between 19 and 45 years old. All participants were healthy but obese based on body mass index measurements.
"MRS has no radiation, is quick to perform and can quantify the amount of fat within bone marrow, muscle and liver," Bredella said.
The findings revealed 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. What's more people with more bone marrow fat content had lower levels of "good" or HDL cholesterol, which is associated with lower risk of heart disease.
Researchers said that higher levels of bone marrow fat puts people at increased risk of fracture.
"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."
Researchers note that triglycerides, the type of fat found in the blood, also had a positive correlation with bone marrow fat. Researchers note that this is because triglycerides stimulate osteoclasts, which are cells that break up bone tissue.
Bredella and her team said the next step is to study the mechanism behind this differentiation of stem cells. Researchers said 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," Bredella explained.