Meta-analyses of the effect of hormone treatment on cognitive function in postmenopausal women.

As we age, most of us experience a certain degree of cognitive decline. In most cases, this decline is gradual. However, in some cases, cognitive impairment is so severe that it can be classified as dementia and this impacts greatly on activities of daily living. Alzheimer's disease, the most common form of dementia, has been linked to the reduction in estrogen levels that comes with aging. More specifically, many researchers have hypothesized that estrogen, and hence estrogen replacement via hormone therapy, could protect against cognitive decline in women. However, recent randomized, controlled trials did not reflect this. In fact, some reports showed that hormone therapy could have detrimental effects on cognitive function in older postmenopausal women. The most publicized of these has been the Women's Health Initiative Memory Study. Studies have thus yielded conflicting results and conclusions. The reasons for this may be due to a number of factors, such as the age of participants, the time of hormone therapy onset ('window of opportunity' theory), type of treatment, type of menopause (surgical or natural) and, possibly, genetic risk factors. We performed quantitative and qualitative meta-analyses and reviewed each of these factors in detail. The future may lie in combining these factors in order to fully understand the potential mechanisms behind estrogen and its effect on cognition.