Introduction: Estrogen has positive effects on bone mineral density (BMD), in particular in trabecular bone through inhibition of bone resorption. Testosterone increases bone size, but the effect on BMD is less clear. Cross-sex hormonal treatment (CSHT) in transgender individuals can affect BMD. Therefore, the aim of this study is to investigate effects of CSHT on BMD during the first year of treatment in male-to-female (MtFs) and female-to-male (FtMs) transgender persons.
Methods: This is a prospective observational study and part of ENIGI (European Network for Investigation of Gender Incongruence). 188 adults who completed one year of CSHT were included. In 99 FtMs and 89 MtFs a dual-energy X-ray absorptiometry was performed to measure lumbar spine (LS) and total hip (TH) BMD before and after one year CSHT. FtMs received intramuscular testosterone undecanoate (1000mg/12 weeks), testosterone gel (50mg/day) or testosterone esters intramuscular (250mg/2 weeks). MtFs were treated with cyproteronacetate (50mg/day) in combination with oral estradiol valerate (2-4mg/day) or an estradiol patch (200ug/week). Analyses were stratified for calcium with colecalciferol (CaD3) use.
Results: In FtMs the mean LS BMD increased with 1.00% (95%CI 0.15 1.85%) and the mean TH BMD with 0.91% (95%CI 0.29 1.53%). In MtFs, the mean LS and TH BMD increased with 3.72% (95%CI 2.85 - 4.59%) and 1.52% (95%CI 0.90 2.14%), respectively. In MtFs who used CaD3, BMD increased more than in patients who did not use this: 4.87% (95%CI 3.49 6.25%) vs. 2.86% (95%CI 1.76 3.95%) in LS, and 2.33% (95%CI 1.27 3.38%) vs. 0.92% (95%CI 0.18 1.66%) in TH. In FtMs, use of CaD3 did not influence the change of LS or TH BMD.
Conclusion: After one year CSHT BMD increases in MtFs more than in FtMs, particularly in lumbar spine. This confirms the role of estrogen on bone in biological males.