The role of hormone replacement therapy in the prevention of Alzheimer disease.

Alzheimer disease (AD) is the most common form of dementia among the elderly. A higher prevalence of AD in women than in men suggests a link between gonadal hormone levels and AD. Increasing evidence supports a role for estrogen in brain regions involved in learning and memory and in the protection and regulation of cholinergic neurons, which degenerate in AD. Despite the lack of consensus, many studies indicate that hormone replacement therapy may decrease the risk for or delay the onset of AD in postmenopausal women. Recent trials have suggested that estrogen treatment may have no significant effect on the clinical course of AD in elderly women with the disease. Thus, the role of estrogen therapy seems to be confined to primary rather than secondary prevention of AD. Ongoing clinical studies may help to determine the role of estrogen in the cognitive function of postmenopausal women and in the prevention of AD.