What is HRT, are there different types?

Hormone Replacement Therapy consists of drugs - in the form of tablets, skin patches or creams - that increase levels of the sex hormone oestrogen. In women who have not had a hysterectomy, the common form of the drug is a combination of oestrogen and the hormone progestogen, which is added to reduce the risk of cancer of the uterus.

Why do women take it?

At the menopause, levels of the sex hormone oestrogen decline, causing symptoms such as hot flushes and contributing to the serious brittle bone disease osteoporosis. HRT can reverse this. Until now, it was also thought to help reduce the risk of heart disease and it's even been said to improve memory.

How big is the risk?

The study showed that among those taking HRT, there was a 26 % increased risk of breast cancer, compared with those taking a dummy pill - and a 29 % increased risk of heart attacks and a 41% increased risk of strokes. By contrast, the risk of hip fractures and of colon cancer were both significantly reduced.

But the researchers point out that presenting the statistics this way can sound more alarming than it should. The findings mean that for over 10,000 women on HRT, you would expect seven more women to have heart attacks and eight more to suffer strokes and eight more to contract breast cancer. There would be six fewer colon cancers and five fewer hip fractures.

Should women be worried about the US study?

Women should be aware of the research but should not be alarmed by it. Though the US form is not available here, it is estimated that a very similar form of HRT is taken by about 300,000 UK women.

However, doctors have long been aware of an increased risk of breast cancer associated with HRT. And it is possible that, for any individual, the benefits of taking the drug will still outweigh any dangers.

But at America's National Institutes of Health, where the work was carried out, researchers say it will be necessary to reconsider the use of this combined oestrogen-progestogen HRT over the long-term.