How does hormone transition in transgender women change body composition, muscle strength and haemoglobin? Systematic review with a focus on the implications for sport participation

Key points

1. 01Haemoglobin and haematocrit normalise to cisgender female ranges within 3-4 months of hormone therapy
2. 02Lean body mass decreases by 3.0%-5.4% after 12 months of hormone therapy
3. 03Muscle cross-sectional area decreases by 1.5%-11.7% over 12-36 months
4. 04Strength losses after 12 months range from non-significant to 7%, well below the ~31%-36% gap between cisgender men and women
5. 05After 36 months, strength and muscle mass in transgender women remain above cisgender female values, suggesting a residual advantage

How it was conducted

Design

Systematic review following PRISMA guidelines

Databases searched

BioMed Central, PubMed, Scopus, and Web of Science (search to April 2020)

Studies included

24 studies published 1999-2020

Participants

Non-athletic transgender women undergoing gender-affirming hormone therapy (testosterone suppression plus oestrogen)

Outcomes

Lean body mass, muscle cross-sectional area, muscular strength, and haemoglobin/haematocrit

Quality

All 24 studies rated moderate quality using the EPHPP tool

What they found

• Lean body mass decreased by 3.0%-5.4% after 12 months of hormone therapy across 7 of 8 longitudinal studies (p<0.05 to p<0.001)
• One cross-sectional study found 17.2% lower lean body mass in transgender women after 48 months compared with cisgender men (p<0.001)
• Muscle cross-sectional area decreased by 1.5%-11.7% over periods of 12-36 months across 4 longitudinal studies
• The largest strength study (n=249) found a 4.3% reduction in hand-grip strength after 12 months (p<0.001); another study found a 7.1% reduction (p<0.001)
• After 48 months of hormone therapy, hand-grip and quadriceps strength were 22.6%-25% lower than in cisgender men (p<0.001), yet remained above cisgender female values
• Haematocrit decreased by 4.6%-14.0% (p<0.01) in 8 of 9 studies; after 3-4 months, haemoglobin/haematocrit levels matched those of cisgender women
• Hormone-naive transgender women had 6.4%-8.0% lower lean body mass and approximately 10%-14% lower hand-grip strength than cisgender men despite similar testosterone levels

Limitations

• All studies were in non-athletic populations, so findings may not reflect changes in trained transgender athletes
• Substantial heterogeneity in hormone regimens and overlapping participant cohorts (particularly in ENIGI studies) precluded meta-analysis
• Most studies only reached 12-24 months of follow-up; data beyond 36 months are sparse
• Studies were conducted exclusively in Western countries and written only in English, limiting generalisability

Why it matters

For patients

Transgender women starting hormone therapy can expect haemoglobin to reach typical female levels within a few months, while muscle and strength changes are more gradual and may not fully equalise with cisgender female averages within the first three years.

For clinicians

When advising transgender women on hormone therapy outcomes, clinicians should communicate that haematological feminisation is rapid (3-4 months) but that musculoskeletal changes are slower and incomplete over 36 months, with implications for sport eligibility policies.

For readers

This review provides the most comprehensive summary to date of physiological changes with hormone therapy in transgender women, but the absence of data from athletic populations and beyond 36 months means sport-specific policy conclusions remain premature.