The controversy over HRT is set to be reignited as a study suggests women in their 50s who use one type of treatment have healthier arteries.
Experts are divided on its health effects after a large US investigation in 2002 turned accepted thinking about HRT on its head by indicating it can increase the risk of strokes and heart attacks.
Both arms of the Women's Health Initiative (WHI) study, involving more than 27,000 people, were immediately stopped three years early as experts argued over the importance of the findings.
The latest results published in The New England Journal of Medicine emerged from a substudy of the WHI focusing on younger postmenopausal women using oestrogen-only HRT.
It claims these women built up fewer calcium deposits in their arteries than women of the same age not undergoing the treatment.
Calcium in the arteries is considered an early warning sign of blocked blood vessels and heart disease.
Lead author Dr JoAnn Manson, chief of preventive medicine at the Brigham and Women's Hospital in Boston, Massachusetts, said: "Although our findings lend support to the theory that oestrogen may slow early stages of plaque build up in the coronary arteries, oestrogen has complex effects and other known risks.
"The results are consistent with our earlier findings that younger women treated with oestrogen had a trend toward fewer heart attacks but, for an individual woman, it remains uncertain whether the benefits of oestrogen outweigh the risks."