Estrogen influences bone metabolism in men
MedWire News: Estrogen levels play an important role in modulating bone metabolism in men, Japanese researchers believe.
Their conclusion comes from a study of bone metabolism in 75 individuals with gender identity disorder, a condition characterized by dissociation between physical gender and psychologic gender identity.
Gender identity disorder is believed to arise from abnormal exposure to sex hormones in the mother's body during fetal life, explain Tsuyoshi Miyajima and co-authors writing in the Journal of Bone and Mineral Metabolism. It is a recognized pathologic condition and may be treated by gender reassignment surgery.
The gender reassignment process comprises three stages: transvestite (TV; involves only changes in appearance such as clothes), transgender (TG; involves the use of hormones), and transsexual (TS; involves genital surgery).
Individuals who undergo gender reassignment therefore represent a unique cohort in which to study the impact of changes in bone metabolism due to the administration of estrogen to a male and testosterone to a female, as well as the removal of existing sex hormones.
Of the 75 patients, 57 were undergoing female-to-male reassignment while the remainder were male-to-female. Transsexuals predominated in both groups while transvestites were in the minority.
As expected, testosterone levels rose and estradiol levels declined as female-to-male individuals progressed through TV, TG, and TS stages. The opposite patterns for testosterone and estradiol were seen in male-to-female patients.
Interestingly, estradiol levels in female-to-male individuals at the TG stage were similar to those seen in healthy premenopausal women, whereas in people at the TS stage they had fallen to levels typically seen in postmenopausal women.
Furthermore, individuals undergoing a male-to-female change showed inhibition of bone resorption (as indicated by urinary levels of cross-linked N-telopeptide of type 1 collagen [NTx]) and increased bone mineral density (BMD) in the lumbar spine.
Conversely, those changing from female-to-male had increased bone resorption and decreased lumbar BMD. Indeed, nine of these patients developed osteoporosis during the course of their gender reassignment and needed pharmacologic treatment.
This resulted in a significant reduction in urinary NTx and a significant increase in BMD within 6 months of starting treatment, say the authors.
Concluding, Miyajima et al write: "These results indicate that estrogen is an important element with regard to bone metabolism in males."
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By Joanna Lyford