Postmenopausal osteoporosis coexisting with sarcopenia: the role and mechanisms of estrogen.

Estrogens (estradiol, estriol, and estrone) are important hormones that directly and indirectly regulate the metabolism and function of bone and skeletal muscle via estrogen receptors. Menopause causes a dramatic reduction in the concentration of estrogen in the body. This contributes to a decline in bone and skeletal muscle function, thereby resulting in osteoporosis and sarcopenia. Menopausal women often experience osteoporosis and muscle wasting, and clinicians recognize estrogen as playing an important role in these conditions, particularly in women. Bone and muscle are closely related endocrine tissues that synthesize and produce various cytokines. These bone- and muscle-derived cytokines, including interleukin-6, irisin, β-aminoisobutyric acid, osteocalcin, fibroblast growth factor-23, and sclerostin, regulate both local and distant tissues, and they mediate the crosstalk between bone and skeletal muscle. This review examines the metabolic effects of estrogen on bone and skeletal muscle and describes cytokine-mediated bone-muscle crosstalk in conditions of estrogen deficiency.