A new study has found that taking sex hormone therapy for a long time may change body composition and increase the risk of cardiovascular problems in transgender individuals.

Research from Sweden’s Karolinska Institutet, published in the Journal of Internal Medicine, provides important insight into the health effects of testosterone and estrogen treatment, particularly in transgender men.

The study tracked 33 adults over six years, 17 transgender men receiving testosterone therapy and 16 transgender women on estrogen.

The findings showed that transgender men experienced a 21% increase in muscle mass within the first year, but a significant 70% increase in belly fat over six years. They also had increased levels of fat in the liver and “bad” LDL cholesterol, putting them at increased risk of heart disease.

Researchers used MRI scans and blood tests to measure changes in muscle mass, fat distribution and metabolic risk factors before, after one year and after five to six years of treatment.

“In transgender men, these changes highlight the need for long-term health monitoring to reduce cardiovascular risks,” Dr. Tommy Lundberg, a researcher at the Karolinska Institutet, said in a statement.

Transgender women, on the other hand, showed more modest changes. Over five years, their muscle volume declined by 7%, although their total fat content increased.

Unlike transgender men, they accumulated less abdominal fat and their muscle strength remained largely stable.

The research highlights the importance of understanding the broader health implications of gender-affirming hormone therapy. “Long-term studies like ours are necessary to address the potential health challenges faced by transgender individuals,” Lundberg said.

Beyond physical health, the study contributes to setting realistic expectations for those seeking masculine or feminine effects through hormone therapy.

The researchers now plan to analyze tissue samples collected during the study to explore how hormone therapy affects gene expression and fat storage mechanisms.

These findings underscore the need for individualized health care approaches and ongoing support to ensure the overall well-being of transgender individuals undergoing hormone therapy.