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Body composition following gender affirming hormone therapy in transgender individuals
For correspondence: Prof Pramila Kalra, Department of Endocrinology, Ramaiah Medical College, Bengaluru 560 054, Karnataka, India e-mail: kalrapramila@gmail.com
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Received: ,
Accepted: ,
Abstract
Background & objectives
Gender-affirming hormone therapy may alter body composition and muscle strength, which may impact participation in sports and other activities. These changes are important to decide whether transgender should have separate categories of competition.
Methods
We conducted this prospective study, to assess the body composition using bioelectrical impedance analysis muscle strength and serum irisin levels at baseline and at 12 months following gender affirming hormone therapy in transgender individuals. The comparisons were done in both cis mode and trans mode.
Results
A total of 32 transfemales and 22 transmales were included in the study. Among transwomen, there was an increase in total subcutaneous fat (9.2%) and visceral fat (11.3 %) (P<0.001 in both cis and trans mode comparison) and a decrease in muscle mass (7.7%) (P=0.033 and P<0.001 in cis and trans mode, respectively) and muscle strength at all sites (P<0.001). Among transmen, there was a decrease in total subcutaneous fat (5.9%) (P<0.001 for both cis and trans mode comparison) and an increase in muscle mass (7.2 %) (P<0.001 for trans mode only) and muscle strength except shoulder abduction on right side (P<0.001). No significant changes were observed in irisin levels following hormonal therapy.
Interpretation & conclusions
Gender affirming hormonal therapy leads to body fat redistribution after twelve months of hormone therapy with significant alterations in muscle mass and strength among both transmen and transwomen. Irisin, an adipomyokine produced through muscle contraction, did not correlate with muscle mass or fat mass on follow up.
Keywords
Body composition
gender-affirming hormone therapy
muscle mass
muscle strength
serum irisin
Gender incongruence, previously known as gender dysphoria, is a condition where an individual's gender identity does not align with the sex assigned at birth1. The diagnosis of gender incongruence follows the DSM-V criteria2. Treatment includes psychological counselling, medical management through gender-affirming hormonal therapy, and surgical interventions like sex reassignment surgery3.
In transmales (on testosterone) and transfemales (on oestrogens and testosterone blockers), muscle mass and strength changes usually become noticeable within the first 3-6 months and may progress for up to 5 years4-7.
The International Olympic Committee in 2019 declared that transmen can compete in the male category without restrictions8. For transwomen, the requirement was set for testosterone levels to be below 2.5 nmol/L for at least twelve months prior to the competition, and if they have taken puberty blockers and not gone through puberty they can compete in the female category. In 2023, the IAAF (International Association of Athletics Federations) further specified that testosterone levels should be under 2.5 nmol/L, and the individual must not have experienced male puberty beyond Tanner stage 28. Concerning gender dysphoric/gender-incongruent adolescents undergoing pubertal suppression, potential risks include adverse effects on bone mineralization, fertility prospects, and cognition9,10. Irisin primarily produced in skeletal muscle, plays a role in the browning of adipose tissue and lipid and energy metabolism11. Some studies suggest that Irisin may have limited or variable effects on muscle strength12. The present study aims to investigate changes in body fat redistribution, muscle mass, muscle strength, and serum Irisin levels after gender-affirming hormonal therapy.
Materials & Methods
This prospective study was carried out at the outpatient department of Endocrinology, Ramaiah Medical College, Bengaluru, Karnataka, India, a tertiary care centre. During a two-year period from (July 2021 to July 2023), transgender individuals who visited were screened after obtaining the ethical clearance from the Institutional Ethics Review Board. The research procedures followed the guidelines laid down in Declaration of Helsinki 1964 and as revised later.
Oral and written informed consent was also obtained from all the participants and use of their data for research and educational purposes was explained.
Study sample and data collection
Those in the age group of 18 to 40 yr who had not previously received treatment, met DSM-V diagnostic criteria, and consented to participate were included in the study and were given the usual standard of care as per the guidelines. Individuals diagnosed with conditions such as diabetes mellitus, thyroid disorders, neuromuscular disorders, HIV, hepatitis, liver failure, chronic kidney disease, Vitamin D deficiency, or chronic systemic illness, and participants on medications that could influence muscle strength or body composition as well as those on long-term steroid therapy, were excluded from participation.
Pilot study
A pilot study involving a small group of 30 individuals was conducted to validate the instruments, receiving approval from a panel of experts. All respondents agreed with the response options, the ease of application, and the adequacy of each instrument. No modifications were suggested by any participant.
Body composition
Participants were instructed to arrive after overnight fasting. Consent was obtained, followed by a comprehensive history-taking and anthropometric examination. Body composition was measured using the bioelectrical impedance analyser (BIA) Omron HBF 375 Karada, in both cis mode (when the participant's gender aligns with their birth-assigned gender) and trans mode (when the participant's gender aligns with their identified gender). The gender of the individual was the assigned gender only from initial recruitment to follow up. The same individual was compared at baseline and follow up in both cis mode and trans mode settings for BIA. There was no control group. Participants were advised to empty their bowel and bladder prior to the procedure.
Muscle strength
Muscle strength was evaluated using a handheld dynamometer, specifically an active force dynamometer, according to the instrument's protocol. The strength of various muscle groups in both the upper and lower limbs was assessed, including hand grip strength. Measurements were taken for muscle groups including shoulder abductors, adductors, elbow flexors, elbow extensors, hip flexors, knee extenders, and hand grip using a digital hand dynamometer. Each participant's muscle strength in these groups was assessed three times, and the average value was recorded. All participants were advised to follow a standard exercise regimen as part of general lifestyle counselling.
Blood samples
Blood samples were collected to assess serum irisin levels using ELISA, as well as serum Vitamin D levels and serum calcium. The serum calcium was analysed immediately, while the samples for Vitamin D and irisin were centrifuged and stored at -80°C. Serum irisin levels were measured using a sandwich ELISA kit (Cusabio Technology LLC, USA). The quantification limit of the assay was 1.8 ng/mL, with intra- and inter-assay coefficients of variation of <15 per cent and <18 per cent, respectively.
Follow up and reassessment
All participants were universally supplemented with Vitamin D according to the guidelines, regardless of their initial Vitamin D status. The individuals were started on gender-affirming hormonal therapy: transwomen received oestradiol valerate and leuprolide, while transmen were given testosterone enanthate injections. All participants were advised to maintain a regular diet and exercise routine. Follow ups were conducted every three months, during which blood tests were used to adjust dosages as needed. Participants who experienced adverse events post-therapy initiation or were lost to follow up, including four transwomen and one transmen were excluded from the study.
Statistical analysis
Descriptive statistics for demographic and clinical data were calculated, with continuous data presented as mean±standard deviation. The Kolmogorov-Smirnov test confirmed parametric distribution. The Student’s t-test was used to compare means between two related groups. P<0.05 was considered statistically significant. All analyses were performed using SPSS version 19 (IBM Corp, Armonk, NY).
Results
After 12 months, body composition, muscle strength, and serum Irisin levels were reassessed.
Participant characteristics
A total of 32 transwomen and 22 transmen participated in this study. Figure illustrates a flowchart of participant selection and follow up in the study. Table I presents comprehensive demographic data including age, body mass index (BMI), oestradiol and testosterone dosages for transwomen and transmen, respectively, levels of oestradiol and testosterone at 12 months, as well as serum levels of Vitamin D, calcium, and HbA1c.
- Flowchart of participant selection and follow up in the study
| Parameters* | Transwomen (n=32) | Transmen (n=22) |
|---|---|---|
| Age (yr) | 27.4±5.3 | 25.2±4.7 |
| Body mass index (kg/m2) | 24.5±6 | 25.8±5.4 |
| Oestradiol valerate dose (mg) | 4.1±1.3 | N/A |
| Testosterone dose (mg) | 150±51.2 | |
| Serum oestradiol levels at 12 months (pg/mL) | 140.6±10.1 | |
| Serum testosterone levels at 12 months (ng/dL) | 524.8±103.5 | |
| Serum Vitamin D (ng/mL) | 24.9±8.5 | 22.8±9.20 |
| Serum calcium levels (mg/dL) | 9.3±0.5 | 8.9±0.23 |
| HbA1c levels (%) | 5.5±0.75 | 5.3±0.40 |
Body composition
Body composition was evaluated at baseline and again at 12 months following the initiation of gender-affirming hormonal therapy, using both cis mode (aligned with the gender assigned at birth) and trans mode (aligned with the participant's gender identity).
Body fat
Table II summarises the changes in total body fat and visceral fat for participants, assessed in both cis mode and trans mode. Among the transwomen (n=32), there was a significant increase (9.2%) in total subcutaneous fat from baseline in both cis mode and trans mode and a significant increase in visceral fat (11.3%) following hormonal therapy. For the transmen, there was a significant decrease (5.9%) in total subcutaneous fat from baseline in both cis mode and trans mode but the change in visceral fat was not significant.
| At baseline (Mean±SD) | At 12 months (Mean±SD) | P value | |
|---|---|---|---|
| Transwomen | n=32 | n=28 | |
| Total subcutaneous fat (%) (cis mode) | 29.09±6 | 31.80±6.19 | <0.001 |
| Visceral fat (%) (cis mode) | 8.40±6.67 | 9.05±7.10 | <0.001 |
| Total subcutaneous fat (%) (Trans mode) | 28.76±7.34 | 31.26±7.40 | <0.001 |
| Visceral fat (%) (trans mode) | 7.89±6.71 | 8.90±8.10 | <0.001 |
| Transmen | (n=22) | (n=21) | |
| Total subcutaneous fat (%) (cis mode) | 34.19±6.16 | 31.31±6.42 | <0.001 |
| Visceral fat (%) (cis mode) | 9.38±6.13 | 9.29±6.15 | 0.600 |
| Total subcutaneous fat (%) (Trans mode) | 34.49±6.01 | 32.22±6.20 | <0.001 |
| Visceral fat (%) (trans mode) | 9.07±8.79 | 8.77±5.23 | 0.227 |
Muscle mass
Table III details, changes in total muscle mass for participants, assessed in both cis mode and trans mode. Transwomen, exhibited a significant reduction in total muscle mass compared to baseline in cis mode and an even more pronounced decrease in trans mode (7.71%). Conversely, transmen did not show an increase in total muscle mass from baseline in cis mode but showed a significant increase (7.15%) in trans mode.
| At baseline (Mean±SD) | At 12 months (Mean±SD) | P value | |
|---|---|---|---|
| Transwomen | (n=32) | (n=28) | |
| Total muscle mass (kg) (cis mode) | 31.15±3.97 | 29.55±5.16 | 0.033 |
| Total muscle mass (kg) (trans mode) | 30.05±4.95 | 27.90±4.78 | <0.001 |
| Transmen | (n=22) | (n=21) | |
| Total muscle mass (kg) (cis mode) | 26.27±2.76 | 27.03±2.40 | 0.205 |
| Total muscle mass (kg) (trans mode) | 26.17±3.11 | 28.04±3.38 | 0.001 |
Muscle strength
Table IV summarises the muscle strength in transwomen and transmen at baseline and 12 months. After gender-affirming hormonal therapy, transmen experienced a significant increase in overall muscle strength, while transwomen showed a significant decrease.
Serum irisin
The serum irisin levels at baseline and after 12 months of gender-affirming hormonal therapy in transwomen were 15.41±3.95 and 15.37±5.00 ng/mL, respectively (P=0.19). The serum irisin levels in transmen at baseline and 12 months follow up were 18.98±5.83 and 19.17±4.74 ng/mL; P=0.90. No correlation was found between irisin levels and muscle mass (transwomen r=-0.01, P=0.94 and transmen r=-0.11, P=0.61) or body fat (visceral fat; r=0.33, P=0.08 , subcutaneous fat r=0.31, P=0.10 in trans women; visceral fat r=-0.42, P=0.06 and subcutaneous fat r=-0.02, P=0.93 in trans men) on follow up.
| Muscle group | Transgender |
At baseline (Mean±SD) n=32 (Transwomen) n=22 (Transmen) |
At 12 months (Mean±SD) n=28 (Transwomen) n=21(Transmen) |
P value |
|---|---|---|---|---|
| Shoulder abduction (Right) | Transwomen | 3.31±0.72 | 2.50±0.68 | <0.001 |
| Transmen | 2.51±0.9 | 3.55±0.67 | 0.144 | |
| Shoulder abduction (left) | Transwomen | 3.30±0.65 | 2.48±0.54 | <0.001 |
| Transmen | 2.61±0.93 | 3.32±0.91 | <0.001 | |
| Elbow flexion (Right) | Transowomen | 4.48±0.85 | 3.75±0.84 | <0.001 |
| Transmen | 3.20±0.94 | 3.81±0.96 | <0.001 | |
| Elbow extension (Right) | Transwomen | 4.61±1.20 | 3.81±1.16 | <0.001 |
| Transmen | 3.42±0.77 | 4.23±0.99 | <0.001 | |
| Elbow flexion (Left) | Transwomen | 4.84±1.08 | 3.74±0.94 | <0.001 |
| Transmen | 3.37±0.91 | 4.03±0.89 | <0.001 | |
| Elbow extension (Left) | Transwomen | 4.76±1.29 | 3.65±1.13 | <0.001 |
| Transmen | 3.26±0.88 | 3.96±0.87 | <0.001 | |
| Hand grip (Right) | Transwomen | 25.00±3.56 | 22.41±3.30 | <0.001 |
| Transmen | 21.60±3.78 | 23.96±3.35 | <0.001 | |
| Hand grip (Left) | Transwomen | 23.60±3.42 | 32.35±3.55 | <0.001 |
| Transmen | 20.00±4.66 | 22.56±5.05 | <0.001 | |
| Hip flexion (Right) | Transwomen | 7.38±1.45 | 6.27±1.24 | <0.001 |
| Transmen | 6.47±1.04 | 7.23±0.10 | <0.001 | |
| Hip flexion (Left) | Transwomen | 7.47±1.45 | 6.36±1.13 | <0.001 |
| Transmen | 6.36±1.25 | 7.25±1.17 | <0.001 | |
| Knee extension (Right) | Transwomen | 7.80±1.32 | 6.70±2.34 | <0.001 |
| Transmen | 6.73±1.17 | 7.68±1.25 | <0.001 | |
| Knee extension (Left) | Transwomen | 7.50±1.43 | 6.56±1.28 | <0.001 |
| Transmen | 6.35±1.50 | 7.07±1.46 | <0.001 |
Discussion
The study showed that gender-affirming hormonal therapy impacts body fat redistribution, causing modest changes in visceral fat and significant alterations in muscle mass and strength in both transmen and transwomen, without major changes in serum irisin levels. Irisin, an adipomyokine produced by muscle contraction, did not show a strong correlation with changes in muscle mass or fat mass.
Ideally, body composition should be assessed using DXA, but it was compared with Bioimpedance Analysis in the present study13,14.
In the present study, transwomen exhibited a 9.18 per cent increase in total body subcutaneous fat after 12 months of oestrogen therapy in both cis and trans modes. This aligns with findings by Alvares et al15, and Yun et al16, and a meta-analysis by Fighera et al17, which also reported similar results. Conversely, transmen showed a significant decrease of 5.9 per cent in total subcutaneous fat after 12 months of gender-affirming hormonal therapy. Comparable outcomes were observed in the study by Caenegem et al18 and Ford et al7. Oestradiol and testosterone significantly influence body fat distribution in both men and women, exhibiting sexual dimorphism between sex hormones and body fat. In cismen, androgens are inversely related to visceral fat, whereas they are directly proportional in ciswomen19. The study by Klaver et al20 found an insignificant increase in visceral fat in transwomen, despite an increase in total body fat. However, our study reveals a significant increase in visceral fat of about 11.3 per cent transwomen, which might be attributed to the Y-Y paradox, a phenomenon commonly observed in the Indian phenotype21.
The change in visceral fat among transmen was insignificant in the present study. Some studies have shown a significant increase in visceral fat among transmen after starting gender-affirming hormonal therapy20. The varying results in our study compared to others might be attributed to the societal norms influencing the lifestyle choices of transmen in our cohort, potentially impacting their health outcomes. In the current study, transwomen showed a significant decrease in muscle mass of 7.71 per cent after 12 months of gender-affirming hormonal therapy. This finding aligns with Klaver et al20 longitudinal study of 179 transwomen, which observed similar results. Another two-year study reported a 5 per cent decrease in lean mass percentage in transwomen one year following the initiation of gender-affirming hormonal therapy18,20. In the present study, transmen demonstrated a significant increase of 7.15 per cent in muscle mass after 12 months of gender-affirming hormonal therapy with testosterone when comparison was done in the trans mode but not in cis mode. This is consistent with longitudinal studies showing approximately a 10 per cent increase in muscle mass among transmen during the first year of treatment20. In the current study, we observed a significant increase in muscle strength across various muscle groups among transmen. Some studies have assessed hand grip strength using a dynamometer. A prospective study involving 23 transmen noted an average 18 per cent increase in hand grip strength at 12 months18. Similarly, a longitudinal study involving 278 transmen reported an 18 per cent increase in hand grip strength from baseline22.
In transwomen, various longitudinal and cross-sectional studies assessing hand grip strength have yielded mixed results. Some indicate a significant reduction in muscle strength, while others show no significant difference18. Additionally, a study examining knee flexion and extension strength in transwomen after 12 months of gender-affirming hormonal therapy found no significant changes23
The current International Olympic guidelines allow individuals who have not undergone puberty to participate in women's categories8. However, since pubertal blockade is not widely practiced, those who have already undergone puberty may be at a disadvantage. Irisin, an adipomyokine induced by skeletal muscle contraction, has shown varied correlations with physical activity in cross-sectional studies12. In the present study, no significant changes in Irisin levels were observed in transmen and transwomen, and these levels did not correlate with muscle mass or strength.
The current study stands out as a prospective observational study, a notable approach in the context of Indian research. Its comprehensive analysis extends beyond the commonly assessed hand grip strength, encompassing multiple muscle groups for a more holistic understanding. However, it is important to acknowledge the limitations: the use of bioelectrical impedance analysis for body fat analysis, though practical, falls short of the precision offered by dual-energy X-ray absorptiometry. Additionally, the operator-dependent nature of muscle strength assessment could introduce variability in the results. These considerations are crucial for a balanced interpretation of the study's outcomes.
Declaration
Authors declare that part of this study with the abstract titled "Effect of gender affirming hormonal therapy on muscle strength, body composition in individuals with gender incongruence" was presented at the ESICON 2022 Conference and published in the Indian Journal of Endocrinology and Metabolism (IJEM) as part of the official conference supplement issue (December 2022 edition). No full text in any form or original article of this study has been published anywhere. This research is original, conducted in accordance with Institutional Ethical Guidelines, and represents the genuine work of the authors. All authors have read and approved the manuscript. There are no conflicts of interest related to this work.
Financial support & sponsorship
This study was funded by the Endocrine Society of India (grant number ESI Grant 2021) awarded to first author (BK).
Conflicts of Interest
None.
Use of Artificial Intelligence (AI)-Assisted Technology for manuscript preparation
The authors confirm that there was no use of AI-assisted technology for assisting in the writing of the manuscript and no images were manipulated using AI.
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