BALTIMORE: A new study shows post-menopausal women who take estrogen can reduce the risk of developing Alzheimer's by 54 percent. The 16-year study, conducted by Johns Hopkins Medical Institutions and the National Institute of Aging, found that estrogen, natural levels of which drop sharply after menopause, may stave off Alzheimer's by stimulating the growth of nerve cells and inhibiting the production of apolipoprotein E, a fatty acid linked to the brain disorder. Scientists also think the hormone helps increase levels of acetylcholine, a crucial transmitter of nerve messages in the brain. The finding helps to support previous indications that estrogen may help prevent the onset of Alzheimer's. Other research, however, suggests that women taking estrogen might be at higher risk of breast and uterine cancer if they have family histories of those diseases.