Until recently, scientists believed bone marrow had mostly a negative effect on health, but mounting evidence supports the idea that the fat tissue inside our bones - known as bone marrow adipose tissue - may be part of the body's endocrine system. Evidence such as a new study that shows bone marrow secretes a little-studied hormone that influences metabolism and is linked to reduced risk of diseases like diabetes.
In the journal Cell Metabolism, researchers from the University of Michigan (U-M), MO, and colleagues explain how bone marrow adipose tissue is a significant source of the hormone adiponectin, which helps to break down fat and maintain sensitivity to insulin. The hormone has also been linked to reduced risk of various obesity-related diseases, including certain cancers, cardiovascular disease and type 2 diabetes.
Bone marrow adipose tissue has traditionally been linked to poor health outcomes
But in this study, where they looked at the role of bone marrow adipose tissue in patients having chemotherapy, or who have anorexia, the researchers found that under conditions where calories are restricted, the fat tissue may also do some good.
Senior author Ormond MacDougald, professor of internal medicine at U-M, says the findings are important because it appears bone marrow adipose tissue "may have positive, protective roles, and influence adaptive functions outside of the bone tissue, at least during calorie restriction."
"We know that low adiponectin has been correlated with multiple health problems and our findings suggest that an important source of this protein, and potentially others that we haven't identified yet, is the fat tissue inside bone marrow, "explains co-lead author Dr. Erica Scheller, a postdoctoral fellow in Prof. MacDougald's lab at U-M.
Researchers already knew that adiponectin is secreted by white adipose tissue - the common body fat most of us complain about - and plays a key role in helping preserve sensitivity to insulin. High levels of the hormone have been linked to lower risk of diabetes and cardiovascular disease.
Paradoxically, adiponectin levels rise as body fat reduces
However, what is somewhat paradoxical, is that as people lose body fat, so their levels of adiponectin go up and not down as one might expect. Obese people have the lowest levels of adiponectin, which adds to their risk of developing diseases.
The paradox has been teasing scientists for some time. But the team on this latest study suggests the answer has been eluding researchers because they have been limiting their investigations to white adipose tissue, believing this to be the only source of adiponectin.
The new study solves the paradox by showing bone marrow adipose tissue - which increases as a person loses weight - is a previously unrecognized source of adiponectin during calorie restriction.
For their investigation, the team showed bone marrow adipose tissue increases in people with anorexia, and in patients receiving chemotherapy or radiation treatment for ovarian or endometrial cancer.
Also, when they blocked marrow fat formation in calorie-restricted mice, it led to a decrease in blood levels of adiponectin, despite production in white fat tissue being unaffected. This shows bone marrow fat tissue has effects beyond the bone.
Study identifies bone marrow adipose tissue as an endocrine organ
The team concludes that the findings identify bone marrow adipose tissue as "an endocrine organ that contributes significantly" to increased circulating adiponectin under calorie restriction, and perhaps in other adverse states as well.
Co-lead author Dr. William Cawthorn, also a postdoctoral fellow in the MacDougald lab, says:
"These findings really underscore how little we know about marrow adipose tissue, and also the mechanisms affecting circulating adiponectin levels. This is really just the beginning of much further research to better understand these relationships and their implications."
Funds and support for the study came from Eli Lilly and Company and the National Institutes of Health.
In March 2014, Medical News Today learned of another surprising discovery by a team of chemists in the UK who found much of bone comprises shock-absorbing "goo" that stops it shattering. In a PNAS-published study they reported how much of bone is made of a viscous "goo-like" fluid that is trapped between mineral crystals, and suggest the finding will lead to new insights about bone diseases like osteoporosis.