16 July 2013
Fat around muscles and the liver has been identified as a key risk factor in developing osteoporosis.
A study published in the journal Radiology found that obese people with a higher level of fat in their liver, muscle tissue and blood also have high fat level in their bone marrow. This fat inside the bone is what puts them at risk of developing osteoporosis.
Although fat in the belly and around the organs has been considered a risk factor for some time, this research by scientists at the Massachusetts General Hospital and Harvard Medical School, is the first to look at the fat in bone marrow, muscles and the liver.
"Obesity was once thought to be protective against bone loss," said study lead author Dr Miriam A Bredella, a radiologist at Massachusetts General Hospital and associate professor of radiology at Harvard Medical School in Boston.
"We have found that this is not true."
Dr Bredella explained that although other studies tended to focus on how visceral fat affects bone density, this research identified the effects of fat in the tissues inside the bones. Bone marrow can be an important indicator of wider issues, as it is the part of the body that produces stem cells.
The study used MRS scans to get more precise measurements of fat in over 100 men and women aged between 19 and 45 years. All of the participants were considered obese in terms of body mass index, but were otherwise in good health.
It found 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. Interestingly, higher levels of HDL cholesterol, the good cholesterol associated with a lower risk of heart disease, was linked to lower bone marrow fat content
"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 ... 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 explained
She added that higher levels of bone marrow fat cause increased risk of bone 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."
The report also found that high levels of fat in the blood - known as triglycerides - has a positive correlation to fat in bone marrow. The research explained that this might be due to triglycerides having a stimulating effect on osteoclasts - the cells responsible for breaking down bone tissue.
However, Dr Bredella said more research is necessary to identify the processes behind the differentiation of stem cells.
“Obesity can shift stem cell lineage, resulting in more bone marrow fat,” she stated.
It follows research last week that revealed having a pot belly - even with a normal BMI - increases a person’s risk of heart disease and cancer. Carrying fat around the middle is a higher risk factor than being obese or carrying fat elsewhere.