Determinants of Bone Mineral Density in Transgender Youth

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.

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.

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 (R ²=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.

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.