Context: Female-to-male transsexual persons (transsexual men) undergo extreme hormonal changes due to ovariectomy and testosterone substitution, allowing studies on sex steroid effects on bone geometry and physiology in the adult.
Objective: The objective of the study was to examine the effects of cross-gender sex steroid exposure on volumetric bone parameters in transsexual men.
Design: This was a cross-sectional study.
Setting: Participants were recruited from the Center for Sexology and Gender Problems at the Ghent University Hospital (Ghent, Belgium).
Participants: Fifty transsexual men after sex reassignment surgery with 50 age-matched control women and an additional 16 transsexual men before testosterone substitution and sex reassignment surgery with 16 control women participated in the study.
Main outcome measures: The main outcome measures were areal and volumetric bone parameters using dual-energy X-ray absorptiometry and peripheral quantitative computed tomography, body composition (dual-energy X-ray absorptiometry), sex steroids, markers of bone turnover and grip strength.
Results: Before hormonal treatment, transsexual men had similar body composition and bone geometry as female controls. The transsexual men on long-term testosterone therapy, however, demonstrated a higher lean body mass and muscle mass and a greater grip strength as well as a lower body and subcutaneous fat mass and a larger waist and smaller hip circumference compared with female controls (all P < 0.001). We observed a larger radial cortical bone size (P < 0.001) and lower cortical volumetric bone mineral density at the radius and tibia (P < 0.05) in transsexual men on testosterone therapy.
Conclusions: Transsexual men on testosterone substitution therapy present with a different body composition with more muscle mass and strength and less fat mass as well as an altered bone geometry with larger bones compared with female controls.