HRT appears to slow the cellular clock of women with an Alzheimer gene called ApoE4.
Healthy women with the gene treated with HRT had blood samples taken to establish if rapid biological ageing had begun. They showed no signs of this, but women who did not get HRT did.
The research, published in online journal Public Library of Science ONE, indicates rapid biological ageing might be associated with Alzheimer’s and that HRT can prevent this.
Study leader Professor Natalie Rasgon, from Stanford University in California, said: “This shows that ApoE4 is contributing to ageing at the cellular level well before any outward symptoms of decline become apparent.
“Yet, oestrogen appears to have a protective effect for middle-aged women carrying this genetic risk factor.”
Numerous previous studies have suggested ApoE4 contributes to age-related mental decline and Alzheimer’s. The gene variant is present in about 40 per cent of people with late-onset Alzheimer’s.
Prof Rasgon’s team focused on telomeres – caps on the ends of chromosomes that keep DNA stable and act like genetic fuses.
Every time a cell divides, its telomeres shorten. If they become too short, the cell can die or lose its ability to divide.
This translates to visible signs of ageing, such as wrinkled skin, and other, harmful effects.
Telomere-shortening can be used as a measure of biological ageing. The scientists analysed telomeres from white blood cells in samples from almost 70 healthy women, mostly aged between 45 and 65, on HRT.
Women were divided into two groups. One remained on HRT while the other did not.
Two years later, the telomeres were checked again and the researchers calculated the rate at which their length had changed.
The telomeres of women carrying the Alzheimer’s gene were six times more likely than those of non-carriers to have undergone significant shortening over the two-year period.
On average, telomeres of women with ApoE4 had shortened by an amount expected over a decade, meaning they had aged five times faster than non-carriers. But HRT cancelled out the negative impact of the gene.
“Our take-home findings were first, that ApoE4 carriers are at greater risk of biological ageing and second, that if you were a post-menopausal ApoE4 carrier, being on oestrogen therapy was a good thing,” Prof Rasgon said.