LOS ANGELES, CA (Catholic Online) - About 25 to 30 percent of the population carries at least one copy of APOE-e4. Each person inherits two copies, one from each parent. Forty percent of people with Alzheimer's disease are carriers.

In the study, scientists observed 63 post-menopausal women, with an average age of 58 over a two year period. The women had been voluntarily taking hormone replacement therapy, either estrogen alone or estrogen plus progesterone for at least one year. All of the test subjects were deemed at risk for Alzheimer's disease due to a family history of the condition.

It must be noted that only 24 of the women were APOE-e4 carriers and all but one study participant was white.

At the beginning, baseline length measurements of each woman's telomeres were taken. A telomere is a "cap" on the end of each chromosome that protects the genes on the chromosome from deterioration.

Every time a cell replicates, its telomeres shorten a little bit, which has been associated with a number of aging-related diseases, including Alzheimer's.

Half of the women were then randomly assigned to stop taking hormone therapy while half stayed on it. After two years, the researchers measured the length of each woman's telomeres again.

The researchers found that women who were APOE-e4 carriers were six times more likely than non-carriers to exhibit obvious telomere shortening once they stopped taking hormones. APOE-e4 carriers experienced more rapid telomere shortening than non-carriers, suggesting that their cells had aged the equivalent of seven to 14 years over the course of the two-year study.

APOE-e4 carriers who remained on hormone replacement therapy showed no evidence of telomere shortening during that time.

"Our results suggest that for women with this genetic variant, hormone replacement therapy may reduce the risk for cellular aging, which may also reduce their risk of dementia," Heather Kenna, a doctoral student in clinical psychology at Stanford University says.

"However, we cannot make recommendations on hormone therapy from this one study alone or suggest that it will decrease risk of dementia."

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