Heart disease often requires complicated surgery

The research, published in the journal Cardiovascular Research, found that genetic receptors for oestrogen become clogged up with other molecules.

When hardened arteries taken from women with known heart disease were compared with unhardened arteries, there were almost three times more clogged, or "methylated" genes.

'A significant step'

Dr Wendy Post, who led the research team, said: "We've been looking for the link between oestrogen, menopause and atherosclerosis (hardening of the arteries).

"Having oestrogen receptor genes shut down so tissues can't respond to oestrogen appears to be a significant step."

Other studies have found that the older the person the more likely they are to have more methylated genes.

However, there are still clear clinical benefits to taking HRT, not least of all, the protection it offers from brittle bone disease, or osteoporosis.

It also reduces the symptoms of the menopause, such as hot flushes or mood changes.

Another study has shown that this protection extends into the mouth, with women who take HRT enjoying better dental health.

Research found that oestrogen supplements may reduce gum inflammation and protect the fibres and bone which support the teeth.

Dr Richard Reinhardt, of the University of Nebraska Medical Center said: "For women at risk for osteoporosis, which likely makes them more vulnerable to rapid periodontal bone loss, this may be yet one more reason to be on oestrogen.

"However, female smokers should note that the study found that smoking had a greater impact on speeding the progression of periodontal disease that oestrogen deficiency."