More women than men succumb to Alzheimer's disease and a number of investigators have therefore looked at the role of oestrogen levels. Post menopausal women suffer a drop in oestrogen and an increased risk of dementia, and some studies, not all, suggest that women on hormonal replacement therapy (HRT) are protected. This study suggests a number of ways that higher oestrogen levels can be protective and I quote from the first paragraph:
"Alzheimer’s disease (AD) is a progressive neurodegenerative disorder characterized by selective neuronal loss in the hippocampus and temporal cortex along with distinctive hallmark pathologies such as neurofibrillary tangles (NFTs) and senile plaques.
Multiple studies demonstrated that the incidence and prevalence of AD is higher in women than in men. The female predominance for developing AD suggests the involvement of gender specific factor(s) in the pathogenesis of AD. Estrogen, which belongs to the category of neurosteroids, appears to be involved in cognition and memory as well as sexual behavior. There is a loss of cognitive enhancing effect of estrogen with advanced age likely linked to age-related changes in the expression and signaling of the estrogen receptors (ERs). Not surprisingly, estrogen loss in menopausal women has been suspected to be closely related with the occurrence of AD. Along this line, some clinical and experimental studies supported a preventive role of estrogen replacement therapy in cognitive deterioration-related disease, such as AD, although it should be noted that several other studies failed to replicate such beneficial effects. Estrogen acts as a neuroprotectant by reducing toxicities of glutamate and amyloid beta (Aβ), by enhancing synaptic plasticity, regulating neurotrophic factors, facilitating transcription factor activation, reducing inflammation in the brain, and by decreasing the hyperphosphorylation of tau."