LONDON -- Using combined hormone replacement therapy (HRT) to relieve symptoms of the menopause can double a woman's normal risk of developing breast cancer, health experts warned Friday.

HRT replaces the natural hormones in the body to relieve unpleasant symptoms of the menopause such as hot flushes and mood swings. It also reduces the risk of osteoporosis, or brittle bone disease.

Estrogen-only HRT has already been shown to raise the odds of breast cancer. New research by scientists at Britain's Cancer Research UK charity provides evidence that combined HRT -- estrogen and progestagen -- is even more dangerous.

"The risks are substantially greater for combined than other types of HRT," Reuters quoted Professor Valerie Beral, of Britain's Cancer Research UK charity, as telling a news conference.

"This is overwhelming evidence that this is the case," she added.

In the study of more than one million women in Britain aged 50-64 who filled in a detailed questionnaire and were followed up for more than two years, Beral and her team found that combined HRT caused four times as many extra breast cancers as estrogen-only HRT.

The results, which are reported in The Lancet medical journal, showed that users of HRT also had a 22 percent higher risk of dying from breast cancer compared to women who had never taken it.

In developed countries in women aged 50-60 there are about 20 breast cancer cases diagnosed per 1,000 women. For the same number of women using estrogen-only HRT for 10 years there will be an additional five cases and combined HRT adds another 19 cases.

"The risk goes up with the duration of use and are apparent within one-two years," said Beral, who headed the research team.

But once a woman stops taking HRT the risks quickly recede. Mounting Evidence

The British research adds to mounting evidence of the dangers of HRT and confusion about the benefits versus the risks of taking drugs. Two smaller studies reported Wednesday found that HRT does not protect women from heart disease and one concluded it may raise the risk of heart attack.

An earlier analysis of four HRT studies by Cancer Research UK found that women who took the treatment for five years had a higher risk of breast cancer, stroke and blood clots in the lung but were less likely to have bowel cancer or hip fractures.

Combined HRT is the preferred type of HRT in Britain and Europe because it lessens the risk of cancer of the womb which is linked with estrogen-only HRT. Beral advised women who are confused about taking HRT to consult their doctor but she added, "There is no simple answer."

She estimates that the use of HRT resulted in an estimated 20,000 extra breast cancer cases in the last decade in Britain in women aged 50-64, with about 15,000 due to the use of combined HRT.