Feb. 25, 2009 -- Women who are fertile for more than 39 years and have natural menopause have a reduced risk of developing Parkinson's disease, according to a new study, while women with four or more pregnancies have a higher risk.
Parkinson's disease is a movement disorder that results in slowness of movement, impaired balance, and tremor and trembling in the extremities and face. It affects about 1 million Americans, according to the Parkinson's Disease Foundation.
Fertile life span is the number of years from first menstruation to menopause. "Thirty five or thirty-six years is about average," says study researcher Rachel Saunders-Pullman, MD, MPH, assistant professor of neurology at Albert Einstein College of Medicine and attending neurologist at Beth Israel Medical Center, New York City.
"It does appear that hormones and reproductive factors play a role in the development of Parkinson's disease," she says. Her study will be presented at the American Academy of Neurology's 61st annual meeting in Seattle, April 25-May 2.
Hormonal factors and their possible role in Parkinson's disease have been studied for at least 15 years, says Saunders-Pullman. Parkinson's affects more men than women, she says, with the gender ratio about two to one.
"The question is, 'Why are women at decreased risk? Is there a hormonal role?''' she asks. "Could female hormones be protective?"
Studies have yielded conflicting results, so Saunders-Pullman and her colleagues analyzed the records from the Women's Health Initiative Observational Study, looking at about 74,000 women who had natural menopause and about 7,800 who had surgical menopause.
They divided the natural menopause women into three groups and the surgical menopause into three groups, depending on the length of the woman's fertility, and relied on self-reported data to determine the number of cases of diagnosed Parkinson's disease.
Fertile Life Span and Parkinson's Disease
Among the findings:
- Women who had natural menopause and a fertile life span of more than 39 years had an 18% reduced risk of getting the disease compared to those women fertile for 33 years or less before having natural menopause. No link between fertile life span and Parkinson's disease was found in the surgical menopause group.
- Women who had four or more pregnancies and experienced natural menopause had a 20% increased risk of getting Parkinson's disease compared to women who had three or fewer pregnancies. No link between pregnancies and disease risk was found in the surgical menopause group.
- Women who had natural menopause and used hormone therapy in the past had no increased risk compared to never-users, nor did current users compared to never-users.
- Women who had surgical menopause and had used hormone therapy in the past had double the risk of getting the disease compared to never-users. Current users had no increased risk compared to never-users.
Why multiple pregnancies increases the risk is not known for certain, Saunders-Pullman says. "We speculate because of the multiple postpartum periods, [their] hormone levels drop [repeatedly]," she says of women who give birth four or more times.
The findings in the surgical menopause group, much smaller than the natural menopause group, need more analysis, she says. The study was supported by the National Institutes of Health and The Thomas Hartman Foundation for Parkinson's Research.
The study "suggests there clearly is a hormonal role as far as women developing Parkinson's disease," Saunders-Pullman says. But, she adds, "It is far too premature to consider going on hormone therapy to protect against Parkinson's disease."
"It's worth looking further into this," she says of the association.
"The results remain suggestive but not definitive," says William J. Weiner, MD, chair and professor of neurology at the University of Maryland Medical Center and director of Maryland Parkinson's Disease and Movement Disorders Center, Baltimore, who reviewed the study results for WebMD.
"No practical advice can be given based on these results," he says. "Further, this finding is an association, not a definite cause and result."
In Parkinson's disease, nerve cells in one part of the brain progressively deteriorate. These nerve cells normally produce a crucial brain chemical called dopamine, a chemical messenger that allows communication between areas of the brain important for smooth muscle movement and nerve functioning.
As the disease progresses, those who have it may have difficulty talking, walking, or doing other simple tasks. While there is not a cure, according to the National Institutes of Health, a variety of medications can provide relief from symptoms.