Researchers at Stanford University School of Medicine found that around 20 percent of women carried a gene, known as ApoE4, that increases the risk of dementia and speeds up the ageing of the DNA by as much as four times. However HRT can protect such women by slowing down the ageing process and thus delaying Alzheimer's.
"This shows that [the gene] 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 who are carrying this genetic risk factor", lead researcher Dr Natalie Rasgon said.
The study has been published in the journal PLOS ONE.