Determinants of Bone Mineral Density in Transgender Youth

Purpose: We aimed to study determinants of bone health in transgender youth in anticipation of or shortly after initiating puberty suppression and/or gender-affirming hormone therapy. Methods: This was a retrospective review of records of transgender adolescents in our institution between June 2014 and June 2019. Dual energy X-ray absorptiometry was used to assess bone mineral density (BMD). Baseline characteristics were collected and included in a multilinear regression model to assess determinants of lumbar spine (LS) BMD Z-scores adjusted for age and height and accounting for race. Welch's t-test was used to compare characteristics across genders. Results: One hundred nineteen patient records were analyzed. Forty-six patients (38.7%) were assigned male at birth (AMAB) and 73 patients (61.3%) were assigned female at birth (AFAB). Mean (±standard deviation [SD]) age (years) was 14.7±2.6 for AMAB and 15.0±2.2 for AFAB. The adjusted LS BMD Z-score was lower in the AMAB population with a mean (+SD) of -0.605±1.42 compared with 0.043±1.09 in AFAB (p=0.010). In a multivariate model, AMAB gender, vitamin D deficiency, and lower body mass index (BMI) z-scores were determinants of lower LS BMD Z-scores (R2=0.206). Age, race, ethnicity, insurance status, and Tanner stage were not determinants of BMD. However, post hoc analysis did show that pubertal status modified the results. Conclusion: AMAB transgender adolescents have lower BMD compared with AFAB patients, before or shortly after starting puberty suppression and/or gender-affirming hormone therapy. Lower BMI and vitamin D deficiency were determinants of lower BMD. Further studies are needed to explore etiology for bone health discrepancy in this population.