Using health record data from the Rochester Epidemiology Project, the study included 2,750 women who had undergone surgery to remove both ovaries, a procedure called bilateral oophorectomy, and 2,749 who had not. The reasons for the surgery were either a benign (noncancerous) condition—such as endometriosis, cyst, or other reason—or for the prevention of cancer. Researchers found that for every 48 women younger than 43 at the time of surgery, one additional woman developed Parkinson’s compared to women of the same age who did not have their ovaries removed.
Parkinson’s disease is a progressive disorder that affects the nervous system and parts of the body controlled by nerves. Tremors are common, but the disorder also may cause stiffness or slowing of movement. It often is accompanied by dementia, sleep disorders, and bowel and bladder problems. Parkinsonism is a general term for slowness of movement along with stiffness, tremor or loss of balance.
Parkinson’s disease manifests almost twice as commonly in men than women in the general population, thus suggesting that sex- or gender-related factors play a role. For women, the ovaries are the main source of the hormone estrogen. Surgical removal of a woman’s ovaries may be recommended because of cancer, gene mutations, and other conditions. When a woman’s ovaries are surgically removed before she goes through menopause, that source of estrogen and other hormones is lost, so removal causes an abrupt endocrine dysfunction.
The findings confirm a 2008 study that suggested lack of estrogen caused by removal of both ovaries in younger women may be associated with an increased risk of Parkinson’s disease and parkinsonism. The results support current guidelines that removal of both ovaries should not be performed to prevent ovarian cancer in women who are at average risk of cancer, says Walter Rocca, M.D., a Mayo Clinic neurologist and epidemiologist and first author of the study.
For women who carry a high-risk genetic variant for ovarian cancer, ovary removal before menopause may be indicated, but women should receive estrogen therapy after surgery up to age 50 or 51, the approximate age of spontaneous menopause, he says.
“As of today, it is not recommended to use estrogen therapy for the prevention of dementia or parkinsonism after spontaneous menopause in women who are age 46 to 55,” says Dr. Rocca. “But this study and previous studies suggest that estrogen therapy is important in women whose ovaries were surgically removed younger than age 46. Particularly vulnerable are women who underwent this surgically induced menopause before age 40.”
This research was funded in part by the National Institute on Aging (National Institutes of Health). A full list of authors and affiliations is in the research article.