It’s been unclear whether hormone therapy helps older women reduce their risk of Alzheimer’s or in fact increases the risk. To date, the research has been inconsistent, with observational studies showing a reduced risk, and a large randomized controlled trial showed an increased risk. As mentioned before, the answer to the inconsistency may lie in the timing of the therapy. A new study supports this view.
The 11-year study (part of the Cache County Study) involved 1,768 older women (65+), of whom 1,105 women had used hormone therapy (either estrogen alone or in combination with a progestin). During the study, 176 women developed Alzheimer's disease. This included 87 (7.9%) of the 1,105 women who had taken hormone therapy, and 89 (13.4%) of the 663 others.
Women who began hormone therapy, of any kind, within five years of menopause had a 30% lower risk of developing Alzheimer's within the study period (especially if they continued the therapy for 10 or more years). Those who began treatment more than five years after menopause, had a ‘normal’ risk (i.e., not reduced or increased). However, those who had started a combined therapy of estrogen and progestin when they were at least 65 years old had a significantly higher risk of developing Alzheimer’s.
The findings support the idea that the timing of hormone therapy, and the type, are critical factors, although the researchers cautiously note that more research is needed before they can make new clinical recommendations.
 Hormone therapy and Alzheimer disease dementia New findings from the Cache County Study. Neurology [Internet]. 2012 ;79(18):1846 - 1852. Available from: http://www.neurology.org/content/79/18/1846