Anorexics Store Fat in Bone Marrow

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Females who are anorexic may look emaciated on the outside, but on the inside they may be storing excess fat in their bone marrow. That is what researchers at Children’s Hospital Boston found during a recent study.

The results of this study are especially important because girls and women who are anorexic typically lose bone mass, making them at great risk for osteoporosis and bone fractures. The National Institute of Arthritis and Musculoskeletal and Skin Diseases notes that girls with anorexia are less likely to achieve their maximum bone density and therefore may place themselves at increased risk for osteoporosis and fractures early and throughout their lives.

In the current study, researchers took magnetic resonance images (MRIs) of the knees of 20 girls with anorexia and 20 healthy girls of the same age (average, 16 years). The images were read by radiologists who did not know the patients’ condition. When the images of the anorexic girls were compared with those of the controls, the patients with anorexia had markedly increased fat, or “yellow marrow,” and less than half as much healthy red marrow in their knees. This was obvious in both the lower thigh bone and upper shinbone.

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Earlier studies have shown that changes in hormones that occur during malnutrition, as in anorexia, trigger the bone marrow’s mesenchymal stem cells to form fat cells rather than cells that form bone (osteoblasts). This may explain why people with anorexia lose bone mass and thus are at great risk of osteoporosis and fractures.

Anorexia has other physical consequences that can affect bone health. The dramatic weight loss experienced by anorexic females causes the body to stop producing estrogen, and low estrogen levels contribute to significant losses in bone density. Anorexics also often produce excessive amounts of the hormone cortisol, which also can trigger bone loss. These factors, along with insufficient intake of calcium and other nutrients necessary for bone health, all contribute to bone loss and the development of osteoporosis.

Anorexia affects up to 5 percent of all female adolescents, according to EatingDisorderClinic.org, and has a higher mortality rate than all other psychological disorders. Only 10 percent of anorexics seek treatment, and 20 percent of those who do not seek treatment will die of disease-related complications.

Catherine Gordon, MD, MSc, director of the Bone Health program at Children’s Hospital Boston and the study’s senior investigator, is planning follow-up studies to determine why excess fat is stored in the bone marrow of anorexics. One hypothesis is that the body is attempting to store energy and preserve warmth, as anorexics often have low body temperatures because they lack insulating fat. Gordon also is interested in how closely fat in the bone marrow is associated with bone density, among other questions.

SOURCES:
Children’s Hospital Boston, news release, Feb. 8, 2010
EatingDisorderClinic.org
National Institute of Arthritis and Musculoskeletal and Skin Diseases

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