From the article:
A sample of 80 women who had used estrogen supplements through menopause was compared with 80 women who had never used estrogen supplements. All had participated in the Nord-Trøndelag Health Study (HUNT), a general population-based study in mid-Norway.
[…]
MRIs of the brains of the women in the study showed that those who had taken estrogen supplements throughout menopause had a larger hippocampus. The hippocampus is one of the most important structures for memory and sense of place, and is one of the structures that is affected early in the progression of Alzheimer’s disease.
“We also examined the shape of the hippocampus and found that areas where hormone therapy had the greatest effect are the same areas that are affected by Alzheimer’s disease in its early stages,” says Pintzka.
Other studies have shown that women who start estrogen supplements several years after menopause do not benefit from the same positive effect on the hippocampus.