New research suggests that women who take oral forms of estrogen for hormone replacement therapy may have a higher risk of hypertension than those who use estrogen applied to the skin.
The study, published on June 5 in Hypertension, looked at the association between oral and transdermal estrogen-only hormone replacement therapy and high blood pressure in postmenopausal women.
The research involved 112,240 women 45 years or older who used an estrogen-only prescription for hormone therapy for at least six months between 2008 and 2019.
The scientists obtained blood pressure data from health records and investigated whether oral, transdermal, or vaginal application of estrogen impacted blood pressure at least one year after hormone treatment.
They also looked at the formulations of estrogen used, including estradiol — a synthetic estrogen that mimics what naturally occurs in the body, and conjugated equine estrogen — a form of estrogen derived from animals.
After analyzing the data, the team found that participants taking the pill form of estrogen therapy had a 14% higher risk of developing high blood pressure than those using estrogen applied to the skin.
Moreover, participants taking oral estrogen had a 19% higher risk of developing hypertension than those using vaginal estrogen suppositories or creams.
After factoring in age, the scientist found a stronger association among women younger than 70 compared to older participants.
The type of estrogen used also had an impact on hypertension risk. According to the study authors, compared to participants using estradiol, those who took conjugated equine estrogen had an 8% increased risk of developing high blood pressure.
The authors say that taking higher doses of estrogen or using it longer was also linked to an increased risk of hypertension.
In a news release, lead study author Cindy Kalenga, an M.D./Ph.D.-candidate at the University of Calgary in Alberta, Canada, says, "We know estrogens ingested orally are metabolized through the liver, and this is associated with an increase in factors that can lead to higher blood pressure."
The results of this study suggest that menopausal women who choose to take estrogen should consider the hypertension risks associated with different forms of the hormone. According to Kalenga, women should also consider using estrogen "for the shortest possible time period, based on individual symptoms and the risk–benefit ratio."
Still, the study only looked at estrogen-only hormone therapy, so the results do not apply to those who use estrogen/progestin combination therapy.
Healthcare providers typically prescribe estrogen-only hormone therapy to women who no longer have a uterus and a combination therapy that includes progestin to an individual with their uterus intact. That’s because progestin helps prevent excessive buildup of the uterine lining caused by estrogen.
Moving forward, the researchers plan to expand on these findings and investigate how combined estrogen and progestin and progestin-only hormone replacement therapies impact heart and kidney health.