Alzheimer's disease, a devastating and irreversible brain disorder that slowly destroys memory and thinking skills, is currently ranked as the sixth-leading cause of death in the United States. For most people with Alzheimer's, symptoms first appear in their mid-60s.

Estimates vary, but experts suggest that more than 5 million Americans may have Alzheimer's, characterized by the development of amyloid plaques and neurofibrillary (or tau) tangles, loss of connections between neurons in the brain, and the death of these nerve cells.

As an age-related disorder, Alzheimer's significantly affects more women (65 percent) than men. A woman in her 60s has a 1-in-6 chance of developing Alzheimer's disease during her remaining life, while that figure is 1-in-11 chance for men over 60.

Aside from the fact that women generally live longer than men and have a greater chance of falling victim to this fatal age-related disorder, experts are still mystified as to why women get this neurodegenerative disorder more often than men. A recent study could shed some light on this fact by suggesting that menopause may cause metabolic changes in the brain, increasing the risk of Alzheimer's disease.

A team from Weill Cornell Medicine and the University of Arizona Health Sciences conducted research, suggesting that there may be a critical window of opportunity when women are in their 40s and 50s to detect metabolic signs of higher Alzheimer's risk and take action to reduce that risk.

In this study, Dr. Lisa Mosconi and her colleagues used the imaging test positron emission tomography (PET) to measure the use of glucose in the brains of 43 healthy women ages 40 to 60. Of these, 15 were premenopausal, 14 were perimenopausal, and 14 were menopausal.

The tests revealed the women who had undergone menopause or were perimenopausal had markedly lower levels of glucose metabolism in several key brain regions than those who were premenopausal. Menopausal and perimenopausal participants also showed lower levels of activity for the metabolic enzyme, mitochondrial cytochrome oxidase, as well as lower scores on standard memory tests.

The strong contrast with premenopausal women remained even when considering that the menopausal and perimenopausal women were older.

Notably, this study showed that the loss of estrogen in menopause not only diminishes fertility, but it also contributes to the loss of a key neuroprotective element in the female brain and a higher vulnerability to brain aging and Alzheimer's disease, suggesting that women should receive medical attention in their 40s before any endocrine or neurological symptoms.

According to Mosconi, women may need antioxidants to protect their brain activity and mitochondria in combination with strategies to maintain estrogen levels. The researchers recommend that more research is needed to test efficacy and safety of hormone replacement therapies at the early stages of menopause and to correlate hormonal changes with risk of Alzheimer's disease.