Women who take hormone replacement therapy long-term are more likely to develop a serious disease than be protected against one, researchers suggest.

They based their findings on a study of four separate pieces of research into the effects of HRT.

They concluded six in 1,000 healthy women aged between 50 and 59 will develop breast cancer, stroke or a blood clot in the lung who would not have done so if they had not taken HRT.

For women in their 60s, the overall increase is 6.5 in every 1,000 HRT users.

The average woman simply does not have the information available to allow her to make an informed choice

Dr Malcolm Whitehead, King's College Hospital

In contrast, 1.7 in 1,000 will not develop colorectal cancer or a hip fracture who would otherwise have done so.

The researchers from Cancer Research UK stress it is up to individual women to look at the figures and make their own mind up about HRT based on their own situation and family history.

It has been suggested that HRT use increases the risk of some cancers, particularly breast cancer, but protects against osteoporosis and coronary heart disease.

By the end of the 1990s, an estimated 20 million women in western countries were using the medication.

Around a third of women in their 50s in the UK use HRT for an average of five years.

Protection

Researchers looked at studies examining HRT's effects on seven potentially fatal conditions; breast cancer, stroke, pulmonary embolism, colorectal cancer, hip fractures, endometrial cancer and coronary heart disease.

Only one looked at the effects of oestrogen-only treatments, three others examined drugs which combine oestrogen and progestagen.

The review found HRT users were at an increased relative risk of breast cancer, blood clots in the lung and strokes compared with women who were given dummy pills.

But HRT was found to be protective against colorectal cancer and hip fracture.

There was no significant difference in the risk of endometrial cancer, and not enough information to assess the relationship between HRT use and rarer diseases such as ovarian cancer.

It had been thought that HRT protected against coronary heart disease.

There are many outstanding questions about the effects of HRT

Sir Paul Nurse Cancer Research UK

However a Women's Health Initiative study, recently found it was linked to a 29% increase in heart attacks and increase in other cardiovascular conditions.

Professor Valerie Beral of Cancer Research UK's Epidemiology Unit in Oxford, told BBC News Online: "The purpose of doing this review was to detail all these figures in a way that's comprehendible for women so that they can make a choice."

She said there needed to be more research into areas including the effects of oestrogen only HRT and the medication's effects on rates of rare cancers such as ovarian cancer.

Professor Beral added: "These estimates provide a rough guide to the likely overall change in the incidence of these conditions over a five year period for typical healthy HRT users in western countries.

"Each woman would, understandably, give different weight to the importance of each condition, as well as to the relief of menopausal symptoms."

Dr Malcolm Whitehead, head of the menopause clinic at King's College Hospital, London, told BBC News Online the claim of increased risk for women on HRT was flawed because the studies looked at women who were not healthy.

'Outstanding questions'

He said women in three out of the four studies had heart disease or a history of blood clots, and in the fourth 50% of women were obese and a third were taking high blood pressure medication.

Dr Whitehead added that it was known HRT increased the risk of breast cancer for women in their 50s by 2.5%, but women having periods into their mid-50s had an increased risk of 3%.

But he said women did need more information about HRT.

Sir Paul Nurse, chief executive of Cancer Research UK, said: "There are many outstanding questions about the effects of HRT and further studies are already under way to understand more about how it affects women over long periods of time.

"Judicious data analysis and accurate interpretation of results will continue to be essential."