Bone Density During Transition

Adolescence is a crucial period for building peak bone mass, driven by sex hormones.

Building bone mass during puberty

Adolescence is a crucial period for building peak bone mass, driven by sex hormones. Suppressing puberty with GnRH agonists temporarily slows this process. Research by Vlot and colleagues (2017) showed that adolescents on puberty blockers developed a deficit in bone mineral apparent density (BMAD) that was only partially recovered after starting cross-sex hormones.

Adults on hormone therapy

In adult trans women taking estrogen, bone density generally remains stable. In trans men taking testosterone, bone density increases in some areas. Risk arises when hormones are stopped without replacement—for example, after orchiectomy without estrogen, or with prolonged underdosing.

Recommendations for monitoring

International guidelines recommend a DEXA scan when hormone replacement therapy is started and periodically during treatment, with additional attention for adolescents on puberty blockers and people using hormones over the long term.

What follow-up research showed

Researchers in Amsterdam followed young people who received puberty blockers and then hormones until they reached the age of twenty-two. Bone density, expressed as a deviation from the average for age and sex, declined while they were taking blockers and had not recovered in transgender women at that age. An analysis of data from the English youth clinic found a similar pattern: after two years on blockers, a significant proportion of young people had bone density well below the average for their age. The Amsterdam study is discussed on puberteitsremmers.nl, and an overview of what blockers do to the bones is available on puberteitsblokkers.nl. The way the dossier on blockers was compiled is described in the archive description of puberteitsremmers.nl.

Why this matters

Approximately ninety percent of bone mass is built before the age of twenty. What is not built during those years is difficult to make up later. A lower peak bone mass increases the risk of osteoporosis and fractures later in life. Whether this group actually experiences more fractures is not known, because the first generation of treated young people is still too young to determine this. The Cass Review cites uncertainty about bone health as one of the reasons for caution.

What you can do yourself

Adequate calcium and vitamin D, weight-bearing exercise and not smoking help protect the bones. Bone density should be measured periodically during treatment with blockers. Ask about the results and what happens if they are unfavorable. See also puberty blockers, GnRH agonists and side effects of hormones.