Postmenopausal therapy with estrogen may increase the risk of Parkinson’s disease in women who have had a Hysterectomy, according to new study findings.. However, hormone replacement therapy in women who go through natural menopause does not appear to increase the risk.

Dr. Rita A. Popat, of Stanford University School of Medicine, California, and colleagues examined the associations of reproductive factors and postmenopausal hormone use with the risk of Parkinson’s disease in postmenopausal women.

As reported in the medical journal Neurology, the study included 178 women with Parkinson’s disease and a randomly selected group of 189 similar women without the disease who were enrolled in the Kaiser Permanente Medical Care Program.

The researchers report that the association between postmenopausal hormone use and Parkinson’s disease risk depended on the type of menopause.

Estrogen therapy was associated with 2.6-fold increased risk of Parkinson’s disease among women with a history of hysterectomy with or without removal of the ovaries, compared with women who never used estrogen. Disease risk increased with longer duration of estrogen therapy.

Hormone use - estrogen alone or combined estrogen and progestin - was not associated with an increased risk of Parkinson’s disease among women with natural menopause.

An association was observed between early age at final menstrual period (44 years or younger) and a reduced risk of Parkinson’s disease.

“At present, there is no apparent biologic explanation for why unopposed estrogen might increase the risk of Parkinson’s disease,” Popat’s team notes.

The findings from animal studies suggest that estrogen can influence dopamine activity, they add. “However, because of differences in experimental conditions, there is no consensus regarding the direction or mechanism by which estrogen influences (dopamine).”

SOURCE: Neurology, August 2005.