Hormonal replacement therapy (HRT) is often suggested as a treatment for women going through menopause, and considering the role that hormones may play in the development of dementia, there have been studies exploring the effects of hormonal replacement therapy on cognitive decline.
There have been a number of studies highlighting the benefits of hormonal replacement therapy, while others found out that it may be, on the contrary, rather dangerous and bad to integrate hormones after menopause, in relation to the risk of developing dementia.
In 2011 a group of scientist conducted a study to find out exactly what effects did hormonal replacement therapy have on the risk of developing dementia later on in life. They found out that integrating hormones in late-life can actually increase the risk of developing dementia, while integrating just for a few years during menopause or right after menopause, had a somewhat protective function. If hormonal replacement therapy was initiated during menopause and continued all the way into late life, the risk associated was the same as the normal population, which suggested that any potentially protective effect provided by integrating hormones during mid-life menopause may actually be counteracted by continuing the therapy in late life.
The scientists therefore refer to a critical window theory, or the correct period, around and right after menopause, in which hormonal replacement therapy is actually considered to be beneficial in reducing the risk of dementia by reducing the deposition of beta-amyloid plaques in the brain, improving the formation of synapses in the hippocampus, and improved brain metabolism.
source: Whitmer, R.A., Timing of hormone therapy and dementia: the critical window theory revisited, Annals of Neurology, 69(1), pp.163-169.