The largest female health study ever carried out has found that use of the contraceptive Pill lowers the risk of stroke, cancer and even heart disease.

The new study, based on 162,000 women, appears to overturn previous findings about the Pill, especially research suggesting that could raise the chance of heart disease. Instead, the Women's Health Initiative suggests that early use of the Pill can offer protection later in life against a range of diseases.

Researchers at Wayne State Univesity in Detroit found taking the Pill lowered the risk of heart attacks, strokes, high cholesterol, high blood pressure and other heart-related problems among the 67,000 women in the study who had ever taken it.

Dr Rahi Victory, the lead researcher, said that overall there was an 8 per cent risk reduction of ever having cardiovascular disease among women who had taken the Pill. "If you use oral contraceptives early on, you're probably going to be protected later in life," he said.

Women on birth control pills also had a 7 per cent lower risk of developing any form of cancer, a small benefit that increased with length of use, Dr Victory said.

Women who took the Pill for four years or more had a 42-per cent lower risk of ovarian cancer and were 30 per cent less likely to develop uterine cancer. No effect was seen on the risk of breast, colon or bladder cancer - but even that was seen as good news because of previous studies suggesting that Pill use made breast cancer more likely.

Experts said the study was especially reassuring because the women it studied were between 50 and 70 years of age, so they would have been on the Pill during its early days when prescribed doses of key hormones were high.

"This is great news because it's a large, randomised, controlled trial, so it's the gold standard of research," said Elizabeth Farrell, consultant gynaecologist and director of the Jean Hailes Foundation, a leading women's research organisation in Melbourne.

Doctors say that the type of hormones and the stage of life when they're used may be what makes them helpful at one point and harmful at another.

"We're still learning more and more about the biology," said Dr Michael Diamond, one of the researchers on the study. Results were presented yesterday at an American Society for Reproductive Medicine conference in Philadelphia.

About 3.25 million in the UK aged 16-49 use the combined oral contraceptive pill. About 16 million American women take the Pill and hundreds of millions have used them since the first one came on the market in 1960.

Most contraceptive pills combine synthetic forms of oestrogen and progestin in various doses. Studies in animals suggest that oestrogen may reduce inflammation in the bloodstream and help prevent deposits from forming and blocking vessels, Dr Victory said.

But women taking these hormones after menopause were more likely to have heart disease and certain cancers, a finding that prompted part of the study to be stopped in 2002.

Dr. Robert Rebar, a gynaecologist who is an executive director of the American Society for Reproductive Medicine, said the type of hormone may make a difference, too. Birth control pills contain four to six times the amount of oestrogen as the lowest formulations of HRT. The most popular form of HRT uses oestrogen derived from horse urine; birth control pills use a synthetic form of it.

The £500-million study was done at 40 locations around America and funded by the National Institutes of Health. Wyeth provided the hormone pills for the menopause portion of the study, but no oral contraceptive makers financed any part of the research.

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