Estradiol and Osteoprotegerin Levels in Patients with Anorexia Nervosa

Bone growth and remodeling is a dynamic process that requires a balance of bone matrix synthesis by osteoblasts and resorption of bone by osteoclasts. Half of patients with newly diagnosed anorexia nervosa have decreased bone mineral density (BMD) at the lumbar spine.

The mechanism involved in the osteoporosis that develops in some AN patients involves receptor activator of nuclear factor K B ligand (RANKL) and osteoprotegerin (OPG), which are important regulators of bone turnover. Patients with AN often have amenorrhea and low serum levels of estradiol (E2). Researchers in Japan recently added new information to the process of bone loss in AN patients.

Dr. Rina Ohwada and colleagues at Tokyo Medical University and Nippon Medical School, Tokyo, investigated serum levels of RANKL OPG and bone turnover markers among 26 young women with AN and 7 age-matched healthy women (Endocr J 2007; published online ahead of release). The team of endocrinologists measured serum levels of estradiol (E2), insulin-like growth factor (IGF-I), and triiodothyronine (T3) and studied their relationship with RANKL and EPG.

Results

Mean body mass index (BMI) of the AN patients was significantly lower than controls (13.8 kg/m2 versus 22.1 kg/m2, respectively; P <0.001), and the mean serum levels of IGF-I, T3, E2 and leptin, which represent nutritional markers among AN patients, were all significantly lower than those among the control women. Serum levels of OPG were higher among the women with AN than in the healthy controls, and were negatively correlated with serum E2 levels of nutritional parameters such as BMI, serum levels of IGF-I, or leptin. Serum levels of OPG were increased despite low serum levels of E2 and leptin. The authors believe their results suggest that serum OPG levels may be increased by a natural compensatory mechanism for estrogen deficiency that is induced by malnutrition.