People with anorexia nervosa have high amounts of fat in their bone marrow, and this may make them prone to osteoporosis. The findings, which were published in the February 2010 issue of the Journal of Bone and Mineral Research, may sound like a big paradox. And though researchers aren't exactly sure how anorexia affects the bones, this study takes them one step further in understanding the correlation.

A research team from Children's Hospital Boston acquired MRI knee images of 40 young women (the average age was 16). Half of the participants had anorexia. The MRI images were then read by radiologists who did not know about the health of the girls.

The 20 girls with anorexia had very high fat content in their bones. The high levels of fat content, called yellow marrow, were correlated to low levels of healthy bone cells. These healthy cells are known as red marrow.

Previous research has suggested that malnutrition causes hormonal changes that can affect bone health. In healthy individuals, mesenchymal stem cells (a type of cell that can become a more specialized type of cell) become osteoblasts (or bone-forming cells). But in people with anorexia, those stem cells instead turn into adipocytes, or fat cells.

Without an adequate amount of osteoblasts, the bones lose mass and become weaker. And for adolescents, it is especially important that the body is able to produce the maximum amount of bone-forming cells. During the teenage years, you grow more bone than you lose. Between the ages of 18 and 25, you reach peak bone mass. This means that most healthy individuals have the greatest amount of bone they will ever have between those ages.

If your bone growth during those formative years is stunted by anorexia, you significantly increase your chances of developing osteoporosis and spinal fractures.

The researchers are currently planning follow-up studies to determine exactly why the body stores fat in the bones of people with anorexia. Additionally, they hope to find an effective way to test hormone therapies that may help build bone mass in people at risk for developing osteoporosis.

To learn more, you can access the full study via this link.