Hormone therapy during menopause is associated with an increased risk of dementia and Alzheimer’s disease, according to a large study published in the journal The BMJ.

Hormone therapy is used to relieve common symptoms of menopause, such as hot flashes and night sweats. Observational studies have previously shown that long-term use of hormone therapy during menopause is associated with the development of dementia, however the effect of short-term use of the therapy and different treatment regimens on the onset of dementia was not known.

Researchers from Denmark evaluated the relationship between the use of combined estrogen and progestogen therapy and the development of dementia according to the type of hormone therapy, duration of use, and age at use.

The research was done on national register data from 2000-2018 for Danish women aged 50-60 years with no history of dementia and no underlying cause preventing them from using hormone therapy during menopause. Factors such as education, income, hypertension, diabetes and thyroid conditions were also taken into account.

5,589 cases of dementia were identified. The average age at diagnosis was 70 years. Before diagnosis 32% of cases had received estrogen-progesterone therapy since the mean age of 53 years. The mean duration of treatment use was 3.8 years.

The results show that compared with people who had never received the treatment, those who had received estrogen-progesterone therapy had a 24% increased rate of developing dementia and Alzheimer’s disease, even among women who were treated at age 55 or younger .

The increase in the occurrence of dementia was seen even in short-term users. Rates were higher with longer duration of use, ranging from 21% for one year or less to 74% for more than 12 years of use. The increased rate of dementia was similar for the continuous (daily) and cyclic (for 10-14 days each month) regimens.

In contrast, treatment with progesterone alone and vaginal estrogen alone was not associated with the development of dementia.

The researchers are calling for further studies to investigate whether this association points to a causal link between hormone therapy and dementia risk.

As they note, “further studies are needed to determine whether these findings represent a true effect of menopausal hormone therapy on dementia risk or whether they reflect an underlying predisposition in women who require these treatments.”