Background: Oestrogen can increase bone mineral density (BMD) by decreasing bone turnover, which is mainly seen in trabecular bone. Testosterone can increase bone size, but the effect on BMD is less clear. Cross-sex hormonal treatment (CSHT) in transsexuals can therefore affect the BMD. For example, in male-to-female individuals (MtFs) a lower BMD before start of CSHT has been described in comparison to healthy control men.
Objectives: To investigate the effects of CSHT on BMD during the first year of hormonal treatment in MtFs and female-to-male individuals (FtMs).
Methods: Prospective study, part of European Network for Investigation of Gender Incongruence (ENIGI). 74 adult patients who completed 1 year of CSHT were included. In 37 FtMs and 37 MtFs a dual-energy X-ray absorptiometry (DEXA) was performed to measure the BMD of the spine at start and after a year of CSHT. The FtMs received testosterone undecanoate i.m. (1000 mg/12 weeks), testosterone gel (50 mg/day), or testosterone esters i.m. (250 mg/2 weeks). The MtF group was treated with estradiol valerate (24 mg/day) or an estradiol patch (200 μg/week) and most MtFs received cyproteronacetate (50 mg/day) simultaneously.
Results: At baseline the BMD of the spine of the FtMs was 0.99 g/cm2 (S.D.±0.10) and after 1 year 1.00 g/cm2 (S.D.±0.10) reflecting a mean difference of 1% (95% CI −0.31 to 2.24). In the MtFs at baseline and after 1 year, the BMD of the spine was 1.00 g/cm2, (S.D.±0.11) and 1.03 g/cm2 (S.D.±0.11) respectively, reflecting a mean difference of 3.6% (95% CI 2.30 to 4.86).
Conclusion: In FtMs the BMD of the spine remained stable after 1 year CSHT. In the MtFs group, the BMD increased on average with 3%. Taken into account the short study period, the change in BMD suggests that BMD is an important variable in the follow up of transsexuals.