BMD higher for transgender men, lower for transgender women vs cisgender controls

Transgender men receiving testosterone have higher total volumetric bone mineral density than cisgender women, whereas transgender women on estradiol have lower volumetric BMD compared with cisgender men, according to study data.

“Bone structure may potentially be impaired in transgender people using feminizing hormones, and whilst further study is needed to work out whether this is attributed to HT, a proactive approach to optimizing bone healthshould be recommended to all transgender people starting feminizing hormones,” Ada S. Cheung, MBBS (Hon), FRACP, PhD, associate professor in the departments of medicine and endocrinology at the University of Melbourne, Australia, told Healio. “Bone structure in transgender people using masculinizing hormones is not compromised.”

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Cheung and colleagues conducted a cross-sectional study of transgender adults aged 18 years and older receiving gender-affirming HT for at least 1 year from April 2017 to April 2018. Participants were recruited from endocrinology and primary care clinics specializing in transgender health in Melbourne. Data from transgender men receiving intramuscular or transdermal testosterone were compared with data from a control group of cisgender women, and data from transgender women receiving oral or transdermal estradiol were compared with those from cisgender men. All participants underwent imaging of the nondominant distal radius and distal tibia. Bone microarchitecture differences were presented in the number of standard deviations (SD) of the mean in cases for transgender participants relative to age-matched cisgender controls.

“We therefore sought to determine whether measurement of microarchitecture will identify any association between gender-affirming hormone therapy and bone morphology,” the researchers wrote. “We hypothesized that in transgender men, testosterone administration is associated with deficits in bone microarchitecture while in transgender women, estradiol administration is associated with preservation of bone microarchitecture.”

The study included 41 transgender men compared with 71 cisgender women, and 40 transgender women compared with 51 cisgender men. Transgender men had 0.85 SD higher total cross-sectional area and 0.63 SD higher total volumetric BMD compared with cisgender women (P = .01 for both). Cortices were 1.11 SD thicker (P < .01) and trabeculae 0.38 SD thicker (P = .05) in transgender men compared with cisgender women.

Transgender women had 0.21 SD lower total cross-sectional area (P = .05) and 0.68 SD lower volumetric BMD (P = .01) compared with cisgender men. Cortical volumetric BMD was 0.7 SD lower (P < .01), cortical thickness was 0.51 SD lower (P = .04) and cortical porosity 0.7 SD higher (P < .01) in transgender women compared with cisgender men. Trabecular bone volume/tissue volume was 0.77 SD lower in transgender women than cisgender men (P < .01), and transgender women had 0.57 SD fewer trabeculae (P < .01) with 0.3 SD greater thickness (P = .02). Trabecular separation was 0.56 SD greater in transgender women compared with cisgender men (P = .01).

“Bone density in trans women was lower than control men,” Cheung said. “We hypothesize that this may be due to low bone density prior to starting feminizing HT — which may be related to various potential factors, such as reduced exercise participation, less physical activity, greater social isolation or low vitamin D levels — or insufficient estradiol levels.”

The researchers said prospective studies are needed to examine the effects of HT on bone microstructure, the effects of treatment on BMD independent of body composition, and whether the differences observed in the study are due to changes among cisgender adults, transgender adults or both.

“Higher doses of estradiol may be needed to offset bone loss, but given the potential for adverse cardiovascular and venous thromboembolic effects, an alternative approach might be administration of bisphosphonate therapy, but further research is needed,” Cheung said.

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