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Feb 26, 2009 -- Women who have more years of fertility (the time from first menstruation to menopause) have a lower risk of developing Parkinson鈥檚 disease than women with fewer years, according to a large new study by researchers at Albert Einstein College of Medicine of Yeshiva University. 鈥淭hese findings, involving nearly 74,000 women, suggest that longer exposure to the body鈥檚 own, or endogenous, hormones, including estrogen, may help protect the brain cells that are affected by Parkinson鈥檚 disease,鈥� says lead author Rachel Saunders-Pullman, M.D., M.P.H., M.S., assistant professor of neurology at Einstein and attending physician in neurology at Beth Israel Medical Center, an affiliate of Einstein鈥檚 in Manhattan. An abstract of the study was released by the American Academy of Neurology (AAN). Further study details will be presented at AAN鈥檚 61st annual meeting in Seattle, April 25 - May 2. After Alzheimer鈥檚 disease, Parkinson鈥檚 disease is the most common neurodegenerative disease. About 1.5 million Americans currently have Parkinson鈥檚, characterized by symptoms that can include tremor (shaking), slowness of movement, rigidity (stiffness) and difficulty with balance. The condition typically develops after the age of 60, although 15 percent of those diagnosed are under 50. There is no cure for Parkinson鈥檚, although medications or surgery can ease symptoms of the disease. Parkinson鈥檚 disease is almost twice as common in men as in women, and researchers have long hypothesized that sex hormones might play a role in the disease. In the current study, researchers analyzed the records of the Women鈥檚 Health Initiative (WHI) Observational Study and focused on those women who developed Parkinson鈥檚 disease. The study involved about 73,973 women who underwent natural menopause. The study found that women who had a fertile lifespan of more than 39 years had about a 25 percent lower risk of developing Parkinson鈥檚 compared with women who had a fertile lifespan shorter than 33 years. In addition, the data showed that women who had four or more pregnancies were about 20 percent more likely to develop Parkinson鈥檚 disease than were women who had three or fewer pregnancies. 鈥淥ne explanation for this finding is that the post-partum period, which is typically one with lower levels of estrogen, subtracts from a woman鈥檚 total fertile lifespan,鈥� says co-author Sylvia Wassertheil-Smoller, Ph.D., professor of epidemiology and population health and the principal investigator of the WHI study at Einstein. 鈥淥verall, our findings might lead one to assume that hormone therapy would make sense as a neuroprotective agent,鈥� says Dr. Saunders-Pullman. 鈥淗owever, we also found that women who were taking hormone therapy did not have a lower risk for Parkinson鈥檚. Thus, our data does not support a role for treatment with exogenous hormones, that is, hormones that originate outside the body, to prevent Parkinson鈥檚.鈥� In fact, hormone therapy can have harmful neurological effects. 鈥淓arlier studies in the Women鈥檚 Health Initiative demonstrated that hormone therapy increases one鈥檚 risk for both stroke and dementia,鈥� says Dr. Wassertheil-Smoller. 鈥淐learly, we need to conduct more research into estrogen鈥檚 effects on the brain.鈥� The study was supported by the Thomas Hartman Foundation for Parkinson鈥檚 Research and the National Institutes of Health.