There are increasing numbers of transgender (otherwise known as trans) which includes people who are undergoing gender-affirming hormone therapy. As many individuals undergo testosterone (in trans men) or estradiol (in trans women) therapy lifelong, long-term effects are important. Given the importance of sex steroids in attaining and maintaining peak bone mass and bone health and strength in adulthood, hormonal fluctuations may upset this balance.
Previous studies in bone health in trans people have used predominantly 2-dimensional areal bone mineral density (aBMD) and suggest that trans people at baseline appear to have lower aBMD than the general population. Lifestyle and environmental factors likely contribute with lower vitamin D levels, higher rates of smoking and lower muscle strength observed, particularly in trans women. Lower estradiol concentrations are associated with a greater decrease in aBMD over time. Only 1 study suggests fracture risk is higher in older trans women compared with age-matched reference men, but no increase was seen in trans men. It is unclear whether this increased fracture risk is related to baseline lower aBMD.
A cross sectional study examining 3-dimensional volumetric bone mineral density (vBMD) has found lower vBMD in trans women compared to cisgender male controls and higher cortical porosity. Trans men had higher vBMD relative to cisgender female controls.
Overall, trans women may not be protected from microstructural deterioration by estradiol therapy, and attention should be made to ensure adequate estradiol concentrations are achieved. Emphasis should also be made on lifestyle factors including encouraging exercise, optimisation of vitamin D and smoking cessation. No adverse effects on bone microstructure appear to occur in trans men. Further long-term longitudinal controlled studies are required, particularly in non-binary individuals using low doses of gender-affirming hormone therapy or in individuals who have previously received GnRH analogues.