For transgender youth, accessing gender-affirming hormone therapy is a key step in helping align their physical characteristics with their gender identity. One aspect of this process is managing the impact of these hormones on growth and height, ensuring that their development is allowed to mirror that of their cisgender peers.

The Role of Hormones in Growth and Development

Height development in adolescents is intricately linked to hormonal changes during puberty. Sex hormones, namely estrogen and testosterone, significantly influence growth spurts and the timing of growth plate fusion in long bones. The effectiveness and impact of estrogen and testosterone on bone development are influenced by the timing, dosage, and individual response to the hormone therapy.

Testosterone is a key driver of bone growth and development during puberty. It not only stimulates the growth and strengthening of bones but also, through its conversion to estrogen, plays a crucial role in the maturation and eventual closure of growth plates. Understanding these effects is particularly important in the context of gender-affirming hormone therapy for transgender youth.

Estrogen is essential for healthy bone development during puberty, contributing to both the growth in height and the attainment of peak bone mass. Its role in the closure of growth plates and regulation of bone density and structure underscores its importance in both natural puberty and gender-affirming hormone therapy.

Puberty blockers are a valuable tool in gender-affirming care, their long-term use without the introduction of sex hormones requires careful consideration and management. The goal is to balance the mental and emotional benefits of gender-affirming treatment with the need for normal physical, sexual, and psychological development. Regular monitoring and personalised care plans are crucial in achieving this balance.

Delaying gender-affirming hormone therapy can affect the final height of transgender individuals, potentially leading to taller stature in transfeminine individuals and shorter stature in transmasculine individuals than might be desired. This highlights the importance of early and individualised intervention for optimal physical and psychological outcomes.

The Role of Testosterone

During puberty, testosterone plays a significant role in bone growth and development, especially in individuals assigned male at birth or those undergoing masculinising hormone therapy.

1. Stimulation of Bone Growth: Testosterone directly stimulates the growth of bone tissue. It contributes to the increase in bone size and density, which is a hallmark of puberty. This is particularly evident in the rapid growth of long bones, contributing to the height increase seen during puberty.
2. Conversion to Estrogen: A crucial aspect of testosterone’s role in bone development is its conversion to estrogen through a process called aromatisation. Estrogen, even in bodies that predominantly produce testosterone, is essential for closing the growth plates (epiphyseal plates) in bones. The closure of these plates at the end of puberty signifies the end of height growth.
3. Muscle Growth and Bone Health: Testosterone also promotes muscle growth and strength. Increased muscle mass places greater mechanical load on bones, which in turn stimulates bone formation and strengthening. This interaction between muscles and bones is important for overall skeletal health.
4. Bone Density: Testosterone contributes to peak bone mass attainment. Higher peak bone mass during adolescence is associated with a reduced risk of osteoporosis and bone fractures later in life.
5. Regulation of Bone Resorption: Testosterone helps regulate bone remodeling by balancing bone formation and resorption (the process by which bone is broken down). This balance is crucial for maintaining healthy bone structure and density.
6. Differential Effects Based on Gender: In transgender adolescents undergoing masculinising hormone therapy, the introduction of testosterone mimics these effects, contributing to increased bone density and changes in bone structure that align with male puberty patterns. The timing and dosage of testosterone are crucial factors in achieving the desired outcomes in bone development.

Testosterone and Height in Transmasculine Youth

• Importance of Timing: For transgender boys and transmasculine individuals, starting testosterone therapy at the appropriate time is important to maximise desired height potential.
• Avoiding Premature Closure: If testosterone therapy starts off too high, it might accelerate growth plate fusion, potentially limiting height. Thus, it’s essential to initiate testosterone therapy at a dose that supports optimal height development.
• Post-Puberty Considerations: Once natural puberty has led to the fusion of growth plates, additional height gain becomes unlikely. Therefore, timely initiation of testosterone therapy is key for transmasculine individuals aiming for additional height.

The Role of Estrogen

Estrogen plays a critical role in bone growth and development during puberty, particularly in individuals assigned female at birth or those undergoing feminising hormone therapy.

1. Growth Spurt Initiation: Estrogen is key in initiating the growth spurt associated with puberty. It stimulates the lengthening of long bones, contributing significantly to the increase in height during this period.
2. Closure of Growth Plates: One of the most crucial roles of estrogen in bone development is the eventual closure of growth plates (epiphyseal plates) in long bones. This process marks the end of the bone growth in length and, consequently, the end of height increase. Estrogen accelerates the maturation and closure of these plates.
3. Bone Density: Estrogen plays a vital role in achieving peak bone mass. It enhances the activity of osteoblasts (cells that form new bone) and decreases the activity of osteoclasts (cells that break down bone). This balance is essential for developing strong, healthy bones and reducing the risk of osteoporosis later in life.
4. Regulation of Bone Remodeling: Estrogen helps regulate the bone remodeling process, ensuring a balance between bone resorption and formation. This regulation is crucial for maintaining bone strength and integrity.
5. Impact on Skeletal Structure: Estrogen influences the shape and structure of the skeleton. In individuals undergoing feminising hormone therapy, estrogen leads to changes that align more closely with typical female skeletal development, such as a broader pelvis.
6. Prevention of Bone Loss: Estrogen has a protective effect against bone loss. Low estrogen levels, as seen in people on puberty blockers for too long without estrogen, postmenopausal women or in conditions like amenorrhea, are associated with decreased bone density and increased risk of fractures.

Estrogen and Height in Transfeminine Youth

• Managing Estrogen Therapy: For transgender girls and transfeminine youth, estrogen therapy plays a dual role. It not only induces feminising physical changes but also regulates height.
• Counteracting Testosterone-Induced Growth: Natural testosterone production during puberty can lead to increased height. Maximising estrogen therapy at the right time can help in limiting this height gain, aligning their development more closely with cisgender female patterns.
• Balanced Approach: The goal is to administer estrogen in a way that supports both feminisation and desired height outcomes, without introducing it so early that it compromises either goal.

The Impact of Puberty Blockers

The use of puberty blockers in adolescents, particularly for those undergoing gender-affirming treatment, is a crucial intervention that can provide significant psychological relief by halting the development of undesired secondary sexual characteristics. However, it’s important to understand why puberty blockers should not be used for an extended period without the subsequent introduction of sex hormones (like estrogen or testosterone).

1. Bone Health: One of the most critical concerns is the impact on bone health. Puberty is a key period for bone development and mineralisation. During this time, individuals typically accrue a significant portion of their bone mass, setting the foundation for bone health in adulthood. Puberty blockers delay this process, potentially leading to lower bone density and an increased risk of osteoporosis later in life. Introducing sex hormones helps in resuming normal bone development and density accrual.
2. Psychological Impact: Extended use of puberty blockers without introducing appropriate sex hormones can also have psychological and emotional impacts. Puberty is not only a time of physical development but also of emotional and social maturation. Delaying this process for too long without a transition plan can lead to feelings of stagnation and social isolation from peers who are progressing through their developmental stages.
3. Sexual and Reproductive Health: Puberty is also a time when sexual and reproductive organs mature. Long-term use of puberty blockers can impact the development of these organs, which may have implications for sexual health and, potentially, fertility in the future.
4. Growth and Development: While puberty blockers can be beneficial in aligning physical appearance with gender identity, prolonged use without the introduction of sex hormones can impact overall growth and development. This includes aspects like height, muscle mass, and fat distribution, which are influenced by sex hormones.
5. Preparation for Adult Health: Adolescence is a critical time for learning to manage one’s health and well-being, including understanding and dealing with hormonal changes. Delaying this process indefinitely can impact a young person’s readiness for adult health responsibilities.
6. Individualised Treatment Plans: It’s essential for healthcare providers to tailor treatment plans to the individual needs of each adolescent. This often includes a strategic plan for the introduction of sex hormones at an appropriate time to ensure healthy development.

The Risks of Delaying Gender-Affirming Care

Delaying gender-affirming care can significantly impact the final height of transgender girls (transfeminine) and transgender boys (transmasculine).

Impact on Transfeminine Individuals (Transgender Girls)

1. Natural Testosterone Effects: If gender-affirming care is delayed for transgender girls, the testosterone present in their body during natural puberty will continue to exert its effects. This includes the typical male growth spurt, which can result in a final height that is taller than the average for cisgender females.
2. Bone Growth and Structure: Testosterone during natural male puberty also influences bone structure, such as broader shoulders, longer limbs and larger hands and feet, and a taller stature.
3. Puberty Blockers and Estrogen Therapy Timing: The timely use of puberty blockers and subsequent estrogen therapy can help prevent these changes by limiting the influence of testosterone on growth. Delaying treatment reduces the opportunity to influence these developmental processes.

Impact on Transmasculine Individuals (Transgender Boys)

1. Natural Estrogen Effects: In transgender boys, the presence of estrogen during natural female puberty promotes a growth pattern typical of cisgender females. This usually results in a shorter final adult height compared to cisgender males.
2. Closure of Growth Plates: Estrogen leads to the earlier closure of growth plates in bones. Therefore, delaying testosterone therapy means that the growth plates may close earlier, limiting height potential.
3. Testosterone Therapy and Growth Potential: Starting testosterone therapy before the closure of growth plates can potentially lead to a growth pattern more aligned with male puberty, which might include an increase in height. However, if gender-affirming care is delayed until after these plates have closed, this opportunity is reduced.

General Considerations

• Individual Variation: It’s important to note that there is significant individual variation in response to hormone therapy. Genetic factors, the timing of puberty onset, and the stage of bone maturation at the start of hormone therapy all play a role in height and bone growth.
• Importance of Timely Intervention: These considerations underscore the importance of timely access to gender-affirming care for transgender youth. Such interventions should ideally be personalised and delivered by healthcare professionals who understand transgender health.

Puberty Blockers: A Strategic Tool

Puberty blockers are often used as an initial step in gender-affirming treatment. They delay the onset of puberty, thereby extending the period during which growth plates remain open.

• Flexibility in Growth: This delay can provide additional time for height growth, especially beneficial for transgender youth who start their transition before or early in puberty.
• Tailored Hormone Introduction: After an appropriate period on puberty blockers, the introduction of gender-affirming hormones (testosterone or estrogen) can be timed to optimise both physical development and height outcomes.

Conclusion

In gender-affirming care for transgender youth, hormone therapy presents an opportunity to align physical development with gender identity while also considering height and growth. The strategic use of testosterone, estrogen, and puberty blockers, tailored to each individual’s developmental timeline, can optimise outcomes. The goal is to provide a balanced approach that respects both the gender-affirming needs and the growth aspirations of transgender adolescents, ensuring their journey is both affirming and healthy.

Further Reading

https://onlinelibrary.wiley.com/doi/10.1111/andr.13034

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9578106/

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9135059/

https://www.gendergp.com/puberty-blockers-bone-health-for-transgender-youth/