Why do so many women get Alzheimer’s?

This video is burning up the Internet this week.

It’s tragic and lovely at the same time, and it comes with a troubling question: Why is Alzheimer’s so much more common in women?

Of the more than 5 million people in the United States who have been diagnosed with Alzheimer’s, two-thirds are women, the Washington Post reports today in an article on new research that might help explain why.

The obvious answer has always been “because women live longer,” and there’s truth to that, of course. Women live about five years longer than men.

But even taking that out of the equation, more women than men get Alzheimers and it’s a particularly important question to answer, especially given that the disease is expected to triple in cases in the next 25 years.

It may have something to do with estrogen.

“We have now seen again and again that women that have [APOe4] (a gene variant) have a much higher risk of getting Alzheimer’s than men of the same age who don’t have the gene,” said Walter A. Rocca, professor of neurology and epidemiology at the Mayo Clinic in Rochester, Minn. He said it’s not fully understood why, but scientists suspect the APOe4 gene appears to interact with estrogen to create the conditions that lead to Alzheimer’s.

Estrogen’s role in Alzheimer’s still remains something of a mystery. The steroidal hormone, which is produced in a woman’s ovaries and adrenal glands, is mostly known for its critical role in promoting female sex characteristics and reproduction. But estrogen also acts as a signaling molecule in genes, cells and organs. And it’s a critical regulator of metabolism in the female brain.

“I call estrogen the Queen of Darwin,” said Roberta Diaz Brinton, a professor at the University of Southern California’s School of Pharmacy who helped organize the Alliance of Women in Alzheimer’s Researchers (AWARE), a professional interest group within the Alzheimer’s Association. She is pursuing clinical trials on a neurosteroid called allopregnanolone that holds promise for regenerating damaged brain tissue.

Brinton thinks the critical moment occurs after menopause, when a women’s estrogen levels drop, triggering a cascading series of effects. Among them is a radical decline in the brain’s ability to burn glucose for energy. Without glucose as a source of fuel, the brain shifts to a backup energy system that burns ketone bodies, which are compounds produced from carbohydrates and fat in the liver.

There was more research some time ago on the effect of hormones in Alzheimers, but it was stopped after it was determined that synthetic estrogen, along with progestin, increased the risk of breast cancer and heart disease in postmenopausal women.

Although the research has restarted, part of the reason there isn’t more on the question, one researcher said, is because of the preponderance of men in the upper levels of Alzheimer’s research.