Hormone replacement therapy and Alzheimer's disease

There is ample evidence to show the beneficial effect of estrogen on the risk and course of Alzheimer's disease (AD). Estrogen may play a role in the pathophysiology of AD through improvement of cerebral blood flow, stimulation of the neuron or gliacyte and interaction with genetic factors. Most etiological studies of estrogen replacement therapy and AD have been retrospective studies. In these studies, the history of estrogen use was obtained from an informant, limiting the validity of the findings. Of the three follow-up studies conducted to date, one has failed to show a protective effect. There is some evidence for a synergistic effect between estrogen and the genetic factors involved in AD. However, up until now, studies of estrogen replacement therapy have generally been too small and of low validity. Large scale, long-term population studies may clarify the role of estrogen replacement therapy in the prevention and therapy of AD.