The study found women with a fertile lifespan of more than 39 years had about a 25 percent lower risk of developing Parkinson's than women with fertile lifespans of less than 33 years.
However, lead author Dr. Rachel Saunders-Pullman of Yeshiva University's Albert Einstein College of Medicine in New York said the researchers stress only longer exposure to the hormones produced by a woman's own body were possibly protecting the brain cells affected by Parkinson's disease.
"Overall, our findings might lead one to assume that hormone therapy would make sense as a neuroprotective agent," Saunders-Pullman said in a statement. "However, we also found that women who were taking hormone therapy did not have a lower risk for Parkinson's. Thus, our data does not support a role for treatment with exogenous hormones, that is, hormones that originate outside the body, to prevent Parkinson's."
The analysis of Women's Health Initiative Observation Study health records for 73,973 women undergoing natural menopause also found women with four or more pregnancies were about 20 percent more likely to develop Parkinson's disease than women with three or fewer pregnancies.
The findings are scheduled to be presented at the American Academy of Neurology's 61st annual meeting in Seattle, April 25 - May 2.
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