Then there is the whole issue of hormone therapy for women. A decade ago, a large U.S. study found that women on estrogen/progesterone therapy had increased risks of blood clots, heart attack, stroke and breast cancer.
And right now, hormones are recommended only when a woman has severe hot flashes or other menopausal symptoms. Even then, experts say, the therapy should be given at the lowest dose and for the shortest time possible.
"It's a complicated issue," Davies noted.
According to study author Rasgon, yet another question is whether middle-aged men with the E4 variant also show relatively speedy telomere shortening. "That's for future, larger studies," she said.
For now, both Rasgon and Davies stressed that people should remember that the E4 gene signals only a relatively increased risk of Alzheimer's. Carrying it does not mean you are destined to develop the memory-robbing disease. And people with other variants can and do develop Alzheimer's.
"In fact, the majority of Alzheimer's disease patients do not carry the E4 (variant)," Davies said.
It's estimated that 40 percent of people who develop Alzheimer's after age 60 have a copy of the E4 gene.
The study was funded by the U.S. National Institutes of Health and the Robert Wood Johnson Foundation Health and Society Scholars Program.
Find out more about ApoE and Alzheimer's from the U.S. National Institute on Aging.
SOURCES: Natalie Rasgon, M.D., Ph.D., professor, psychiatry and behavioral sciences, Stanford University School of Medicine, Stanford, Calif.; Peter Davies, Ph.D., director, Litwin Zucker Research Center for the Study of Alzheimer's Disease, Feinstein Institute for Medical Research, Manhasset, N.Y.; Feb. 13, 2013, PLoS One
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