Biological men who take hormone therapy in order to transition to female are at higher risk of cardiovascular problems such as stroke, blood clots and heart attacks, a recent study that purports to be the largest study of transgender individuals on hormone therapy ever undertaken.
Earlier this month, the academic medical journal Annals of Internal Medicine published a study that focused on the relationship between cross-sex hormone therapy in transgender patients over 18 and the prevalence of acute cardiovascular events.
The study was done by Rollins School of Public Health at Emory University and led by the Kaiser Permanente Southern California Department of Research & Evaluation.
Researchers analyzed data from 5,000 transgender patients within the Kaiser Permanente health system who have taken hormone therapy for the purpose of gender transition. That data was compared with over 97,000 cisgender patients of similar ages and health.
The study found that men who transition to female on hormone therapy were 80 to 90 percent more likely to suffer a stroke or heart attack than biological women. Additionally, transgender women who transitioned through hormone therapy were twice as likely as biological men or women to have a blood clot condition called venous thromboembolism.
"The patterns of increases in VTE and ischemic stroke rates among transfeminine persons are not consistent with those observed in cisgender women," the study concludes. "These results may indicate the need for long-term vigilance in identifying vascular side effects of cross-sex estrogen."
Michael Goodman, Emory University professor of epidemiology and an author on the paper, said in a news release that the study "confirmed elevated risks of certain vascular events related to hormone therapy.
"[T]hese risks need to be weighed against the important benefits of treatment," says Goodman.
While medical professionals and experts critical of hormone therapy have voiced concern for years about the health risks associated with hormone therapy and lack of long-term research in that area, Kaiser Permanente research scientist Darios Getahun told NBC News that there were some limitations to the study that prevent him from being able to place direct causal relationships on the findings.
One concern was that the data was limited to only Kaiser's records and researchers couldn't account for outside medication.
"For now, this study is the best measure we have of the risk, and it's much better than what we've had before," Getahun declared.
Despite the concerns for men transitioning to female, the study reports that the results were insufficient to make conclusions about biological women transitioning to male through hormone therapy.
"The negative impact estrogen has on men (so called trans women) is no surprise," Dr. Michelle Cretella, a longtime critic of hormone therapy and the president of the conservative American College of Pediatricians, told CP in an email. "Regarding the potential negative impact of testosterone upon women (trans men), the absence of evidence is not evidence of absence."
"We have very good reason to be skeptical of this report," she added. "Testosterone lowers good cholesterol, raises triglycerides and elevates homocysteine levels which are all risk factors for cardiac disease. Testosterone may also cause polycythemia, sleep apnea, insulin resistance (type 2 diabetes), and unknown risks to breast, ovarian and uterine tissues."
Cretella also stated that one reason that the study may not found increased heart disease and cancers in transmasculine women is that the study only reviewed medical records from a period of eight years.
"We need to look for these drugs causing disease in the long term: 10, 20 and 30 years out from starting the synthetic hormones," Cretella wrote.
The study comes as scholars have previously raised concern with the increase of gender-confused children being subject to hormone therapy for gender transition without the proper long-term studies to determine the harm being done by such drugs.