Low Bone Mineral Density in Early Pubertal Transgender/Gender Diverse Youth: Findings From the Trans Youth Care Study

CONTEXT: Transgender youth may initiate GnRH agonists (GnRHa) to suppress puberty, a critical period for bone-mass accrual. Low bone mineral density (BMD) has been reported in late-pubertal transgender girls before gender-affirming therapy, but little is known about BMD in early-pubertal transgender youth. OBJECTIVE: To describe BMD in early-pubertal transgender youth. DESIGN: Cross-sectional analysis of the prospective, observational, longitudinal Trans Youth Care Study cohort. SETTING: Four multidisciplinary academic pediatric gender centers in the United States. PARTICIPANTS: Early-pubertal transgender youth initiating GnRHa. MAIN OUTCOME MEASURES: Areal and volumetric BMD Z-scores. RESULTS: Designated males at birth (DMAB) had below-average BMD Z-scores when compared with male reference standards, and designated females at birth (DFAB) had below-average BMD Z-scores when compared with female reference standards except at hip sites. At least 1 BMD Z-score was < -2 in 30% of DMAB and 13% of DFAB. Youth with low BMD scored lower on the Physical Activity Questionnaire for Older Children than youth with normal BMD, 2.32 ± 0.71 vs. 2.76 ± 0.61 (P = 0.01). There were no significant deficiencies in vitamin D, but dietary calcium intake was suboptimal in all youth. CONCLUSIONS: In early-pubertal transgender youth, BMD was lower than reference standards for sex designated at birth. This lower BMD may be explained, in part, by suboptimal calcium intake and decreased physical activity–potential targets for intervention. Our results suggest a potential need for assessment of BMD in prepubertal gender-diverse youth and continued monitoring of BMD throughout the pubertal period of gender-affirming therapy.