Posted by: David Walsh25 JUL 2014
Recent research at the University of Michigan has suggested that adipose tissue contained within bone marrow provides a previously unknown source of a hormone linked with reduced levels of diabetes, cardiovascular disease, and obesity-related cancers. This provides a contrast with previous research, which has almost universally highlighted the risks associated with increased fat levels within bone marrow, in particular its correlation with reduced bone density and consequent weakness.
Bone marrow produces stem cells that can develop into either osteoblasts, responsible for bone formation, or fat cells. A study carried out at Harvard University in 2013 examined how fat levels in the liver and muscles affected those of the bone marrow. It was discovered that high levels of circulating triglycerides and fats in the liver and muscles correlated with high levels of bone marrow fat, but with low levels of the “good” HDL-cholesterol. Furthermore, diet-induced obesity alters the differentiation of stem cells, favouring the formation of fat cells over osteoblasts.
Obesity was once thought to protect against reduced bone density, but it is now known that the opposite is true, and increased visceral fat, as well as muscle and liver fat, have all been shown to have a direct correlation with reduced bone density.
However, the recent results from Michigan suggest that bone marrow adipose tissue does confer some benefits, and may even exert some protective and preventative roles, influencing systems outside of the bone marrow, especially in conditions of decreased calorific intake. The study found that bone marrow is an important but previously unknown source of adiponectin, a hormone which helps maintains the body’s sensitivity to insulin and aids in the breakdown of fats. It has been linked to a decreased risk of cardiovascular disease and diabetes because insulin resistance and obesity are both associated with low plasma adiponectin levels. Previously, white adipose tissue was the sole known source of adiponectin, and it was a puzzle as to why plasma levels increased in, for example, anorexics.
It was known that bone marrow adipose tissue increases as body mass decreases, in conditions where there is insufficient calorific intake, and the discovery that adiponectin is produced from within the bone marrow explains this apparent discrepancy. Adiponectin produced within bone marrow is an important, newly discovered source of the protein, and can be viewed as an endocrine organ that has an influence on plasma levels throughout the body.
William P. Cawthorn, Erica L. Scheller, Brian S. Learman et al. Bone Marrow Adipose Tissue Is an Endocrine Organ that Contributes to Increased Circulating Adiponectin during Caloric Restriction.Cell Metabolism, 2014; DOI: 10.1016/j.cmet.2014.06.003