Does the Duration of Menopause Influence the Risk of Parkinson’s?

About 1.5 million Americans have Parkinson’s disease, which is almost twice as common in women as in women. So, not surprisingly, researchers have wondered if sex hormones play a role in its causation. They used data from the Women’s Health Initiative Observational Study to find out, and will present their results at the American Academy of Neurology meeting in Seattle next April.

Data from almost 74,000 women who underwent natural menopause were analyzed. Factors evaluated included age at menopause, fertile lifespan, number of pregnancies, hormone replacement therapy (HRT), and the occurrence of Parkinson’s disease. Roughly 10% of them had had a surgical menopause, i.e. they had had their ovaries removed surgically.

The fertile lifespan for each woman was calculated as age at menopause minus age at first menstruation. Among the 74,000-odd women who had a natural menopause, those with a fertile lifespan of more than 39 years had about a 25% lower risk of developing Parkinson’s disease than women with a fertile lifespan of 33 years or less. Moreover, women having 4 or more pregnancies were about 20% more likely to develop Parkinson’s than those who had three or fewer pregnancies. The researchers suggest that these two findings show that estrogen can have a protective effect on against Parkinson’s. (Estrogen levels are typically lower for a time after childbirth, so that more pregnancies mean less exposure to estrogen.) However, women taking HRT did not have a lower risk of Parkinson’s, so that exogenous estrogens – i.e. hormones that originate outside the body - have no role to play in therapy to prevent Parkinson’s.

The results of this study are interesting, but don’t have any practical consequences. They serve, rather, to encourage Parkinson’s disease researchers to concentrate efforts on trying to find exactly what estrogen-like substance does offer some protection against the condition.