Transgender women experience only small changes in vitamin D-binding protein after 3 months of estradiol therapy, whereas testosterone therapy was not associated with vitamin D changes in transgender men, according to findings published in The Journal of Clinical Endocrinology & Metabolism.
Transgender people often receive treatment with gender-affirming hormone therapy, and previous studies have shown that sex steroids can influence vitamin D metabolism, particularly vitamin D-binding protein, Paul Lips, MD, PhD, professor of endocrinology at the Center of Expertise on Gender Dysphoria at VU University Medical Center in Amsterdam, and colleagues wrote in the study background.
“This HT might affect the [vitamin D-binding protein] concentration and consequently the bioavailable and free circulating 25-(OH)D concentration,” Lips and colleagues wrote. “Measured total 25-(OH)D might therefore not well represent the bioavailable and free circulating 25-(OH)D in transgender people receiving HT. This may hamper the assessment of vitamin D status and vitamin D deficiency and its potential harmful effects on bone and muscle.”
Lips and colleagues analyzed data from 29 transgender women (mean age, 26 years) prescribed estradiol and cyproterone and 30 transgender men (mean age, 22 years) prescribed testosterone participating in the European Network for Investigation of Gender Incongruence, a prospective, observational study performed in Amsterdam; Florence, Italy; Ghent, Belgium; and Oslo, Norway. Researchers measured vitamin D-binding protein, total 25-hydroxyvitamin D, free 25-(OH)D, albumin, estradiol and testosterone at baseline and after 3 months of HT, and calculated levels of deseasonalized total 25-(OH)D and bioavailable 25-(OH)D. Researchers used linear regression analyses to asses changes in vitamin D-binding protein and changes in estradiol and testosterone, as well as measured and calculated free 25-(OH)D, measured free and total 25-(OH)D concentrations and bioavailable and total 25-(OH)D concentrations.
At baseline, 41% of transgender women and 47% of transgender men had a total 25-(OH)D concentration between 25 nmol/L and 50 nmol/L, and 69% of transgender women and 67% of transgender men were considered vitamin D deficient.
In transgender women, researchers observed a mean 5% increase in vitamin D-binding protein between baseline and 3 months (P = .06) and a mean 2% decrease in measured 25-(OH)D. Total 25-(OH)D levels also increased, but results did not persist after seasonal adjustment, according to researchers. Transgender women prescribed transdermal estradiol tended to experience a larger increase in vitamin D-binding protein vs. transgender women prescribed oral estradiol (difference, 29 µg/mL; 95% CI, –5 to 63); however, the difference did not rise to statistical significance.
Among transgender men, researchers did not observe any changes in vitamin D-binding protein, measured free 25-(OH)D, deseasonalized total 25-(OH)D, bioavailable 25-(OH)D and albumin-bound 25-(OH)D over 3 months of HT.
The researchers observed that each 100 pmol/L increase in serum estradiol concentration was associated with a 3 µg/L increase in vitamin D-binding protein, whereas each 10 nmol/L increase in testosterone was associated with a 3 µg/L decrease in vitamin D-binding protein.
The researchers noted that the cohort was small, the time frame was short and a measured concentration of parathyroid hormone was unavailable, which could be informative due to a high correlation between free 25-(OH)D concentration and serum parathyroid hormone. However, findings suggest any changes in vitamin D levels are small and not statistically significant, whereas total 25-(OH)D concentrations seem to reflect free and bioavailable 25-(OH)D concentrations well.
“Therefore diagnostics of the commonly occurring vitamin D deficiency in trans people does not seem to be hampered by hormonal treatment,” the researchers wrote. – by Regina Schaffer
Disclosures: Lips reports he has received lecture fees from Abiogen. Please see the study for all other authors’ relevant financial disclosures.