Two-year study will examine how gender-affirming hormone therapy affects energy use and blood vessel function
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The research team at the LeiCeM Cluster of Excellence is preparing a new study. It builds on the first phase of the Hormones and Health study (HHS), in which researchers from the Helmholtz Institute for Metabolic, Obesity and Vascular Research (HI-MAG), Leipzig University and the University of Leipzig Medical Center followed trans people undergoing gender-affirming hormone therapy. The second cohort will be studied over a period of two years, with the study expected to begin in early 2027.
"We are interested in two main questions: What are the health effects of hormone therapy for trans people? And what can this teach us more generally about how estrogen and testosterone work in the human body?" says study leader PD Dr. Haiko Schlögl.
Why the study matters for LeiCeM
LeiCeM investigates human metabolism and the development of metabolic diseases. The HHS cohort offers a valuable opportunity for this research: participants are examined before starting hormone therapy and at several points during treatment—after three, six, 12 and 24 months. "By examining the same person before and during hormone therapy, we can track changes much more precisely than if we simply compared two different groups of people," explains Schlögl.
His team is particularly interested in how sex hormones affect body composition, especially the relative amounts of muscle and fat, as well as energy expenditure and the vascular system. The findings could have implications for the health of trans people while also helping researchers better understand the effects of sex hormones in the wider population.
The new phase of the study will involve additional, more precise methods. A metabolic chamber will be used to measure energy expenditure. Further tests will provide detailed information about blood vessel function and how testosterone affects blood flow and markers associated with harmful changes to blood vessels. In collaboration with the Max Planck Institute for Human Cognitive and Brain Sciences in Leipzig, the researchers also plan to use magnetic resonance imaging (MRI) to investigate whether gender-affirming hormone therapy causes changes in brain regions where differences between men and women have previously been observed.
What the first phase of the HHS has already revealed
Around 40 trans people took part in the first phase of the HHS, half of them trans men and half trans women, all of whom were starting gender-affirming hormone therapy. The team investigated changes in several areas, including temperature perception, blood clotting, eating behavior and the carotid artery, as well as energy metabolism, which they assessed using indirect calorimetry with a ventilated hood.
This involves measuring oxygen consumption and carbon dioxide production in the air a person breathes beneath a transparent hood to determine how much energy their body uses at rest. Examinations of cis women and cis men who were not undergoing hormone therapy helped the researchers put their findings into context. The examinations of the first cohort are now being completed, with further analyses and scientific publications in preparation.
The first findings were published in Communications Medicine in 2026. For this paper, the team investigated temperature perception in a subgroup of 12 trans women and 17 trans men before they started hormone therapy and again after three and six months. Previous research had already shown that cis women are better at detecting small changes in skin temperature than cis men.
Among the trans women in the study, sensitivity to changes in warmth and cold increased during treatment with estrogen and a testosterone blocker. The magnitude of this change was roughly equivalent to the previously observed difference between cis women and cis men. "Our findings provide the first evidence that gender-affirming hormone therapy also causes the skin's temperature-sensing system to adapt to the new 'hormonal sex,'" says Schlögl. Further research is needed to establish the precise mechanisms behind this change.
Improving information and support before and during hormone therapy
Too little is still known about the potential health effects of hormone therapy. Schlögl identifies a better understanding of changes in metabolism and the cardiovascular system, as well as resolving unanswered questions about blood clotting, as important research goals. He wants to gain a clearer understanding of the factors involved. Robust evidence could help improve the information provided to patients before they begin hormone therapy and support appropriate medical care throughout treatment.
"Only by understanding the potential risks more fully can we inform people about them and investigate ways to reduce them," says Schlögl.
Medical care also involves access to doctors and psychotherapists with the relevant expertise. A 2026 study by the Medical Center Hamburg-Eppendorf highlights the difficulties trans people can face in accessing such care. Looking at several regions in northern Germany, the researchers found limited access to specialist medical services, a shortage of suitably experienced professionals and, in some cases, long distances to health care providers. The study does not quantify the shortage of services across Germany as a whole. Schlögl also believes that more medical practices are needed to provide care for trans people undergoing hormone therapy.
Publication details
Pauline Zimmermann et al., Changes in temperature perception in transgender persons undergoing gender-affirming hormone therapy, Communications Medicine (2026). DOI: 10.1038/s43856-026-01420-0
Journal information: Communications Medicine
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EndocrinologyReproductive healthPsychology & Mental health Provided by Leipzig University Who's behind this story?
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