Women who were on hormone replacement therapy (HRT) for more than 10 years had a higher risk of developing Alzheimer's disease, according to a study published online in the journal The BMJ on March 6.
HRT helps balance the body's declining production of hormones, including estrogen and progesterone. It also helps alleviate menopause symptoms such as night sweats, hot flashes, and vaginal dryness.
Some research has suggested that HRT is protective against Alzheimer’s disease, but a clinical trial in 2017 demonstrated an increased risk.
To determine the connection between HRT and Alzheimer’s disease, a team of researchers at the University of Helsinki in Finland analyzed data from national registers in Finland to identify 84,739 women who were diagnosed with Alzheimer’s disease between 1999 and 2013. The majority (98.8 percent) were diagnosed at age 60 or older; 56 percent were diagnosed at 80. The researchers matched these women by age and location with the same number of postmenopausal women who did not have Alzheimer’s disease.
A national register that reported hormone therapy since 1994 was used to determine the type of therapy the women underwent—either oral estradiol, vaginal estradiol, estrogen-progestogen (a combination of estradiol and progestogen), or tibolone (a synthetic steroid). The register was also used to determine the duration—three years or less, three to five years, five to 10 years, or more than 10 years. In addition, the researchers noted the age at which therapy was initiated—either 52 or 65.
Women who used oral estradiol, or estrogen-progestogen therapy, had a 9 to 17 percent higher risk of developing Alzheimer’s. No similar risk was seen with vaginal estradiol.
Those who started estrogen-progestogen therapy before age 60 saw an 8 to 17 percent increased risk of Alzheimer’s; the increased risk was associated with 10-year HRT exposure rather than the women’s age, the researchers noted. Neither tibolone use nor shorter stints of HRT were associated with Alzheimer’s risk.
The researchers acknowledged that although the absolute risk for Alzheimer’s disease is small, women who use HRT should be made aware of the risk and they and their doctors should exercise caution.
Long term use of systemic hormone therapy—regardless of the type or when it was initiated—might be accompanied by an overall increased risk of Alzheimer’s disease, the researchers concluded.