The association of gender-affirming hormone therapy duration and body mass index on bone mineral density in gender diverse adults

Introduction: Feminizing and masculinizing gender-affirming hormone therapy (fGAHT, mGAHT) results in bone mineral density (BMD) maintenance or improvement over time in transgender and gender diverse (TGD) adults. Mostly European TGD studies have explored GAHT's impact on BMD, but the association of BMI and BMD in TGD adults deserves further study.

Objective: To determine whether GAHT duration or BMI are associated with BMD and Z-scores among TGD young adults.

Methods: Cross-sectional study of nonsmoking TGD adults aged 18-40 years without prior gonadectomy or gonadotropin-releasing hormone agonist (GnRHa) therapy taking GAHT for > 1 year. BMD and Z-scores were collected from dual-energy x-ray absorptiometry. Associations between femoral neck, total hip, and lumbar spine BMDs and Z-scores and the predictors, GAHT duration and BMI, were estimated using linear regression.

Results: Among 15 fGAHT and 15 mGAHT, mean BMIs were 27.6 +/- standard deviation (SD) 6.4 kg/m² and 25.3 +/- 5.9 kg/m², respectively. Both groups had mean BMDs and Z-scores within expected male and female reference ranges at all three sites. Higher BMI among mGAHT was associated with higher femoral neck and total hip BMDs (femoral neck: β = 0.019 +/- standard error [SE] 0.007 g/cm², total hip: β = 0.017 +/- 0.006 g/cm²; both p < 0.05) and Z-scores using male and female references. GAHT duration was not associated with BMDs or Z-scores for either group.

Conclusions: Z-scores in young, nonsmoking TGD adults taking GAHT for > 1 year, without prior gonadectomy or GnRHa, and with mean BMIs in the overweight range, were reassuringly within the expected ranges for age based on male and female references. Higher BMI, but not longer GAHT duration, was associated with higher femoral neck and total hip BMDs and Z-scores among mGAHT. Larger, prospective studies are needed to understand how body composition changes, normal or low BMIs, and gonadectomy affect bone density in TGD adults.