The Pill can provide protection against ovarian cancer for 30 years after women stop using it

A new study shows the longer a woman is on the Pill, the less likely she is to develop the disease dubbed the "silent killer" because symptoms are often diagnosed too late.

A report today in The Lancet medical journal shows that taking the Pill for 15 years halves the risk of ovarian cancer compared with those who have never taken it.

They claim the benefits outweigh any other slight rise in cancer risk posed by the pill.

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Some experts are calling for the contraceptive pill to become routinely available over the counter in pharmacies - a proposal backed by Health Minister Lord Darzi last year.

But family planning doctors believe it should stay prescription-only so women get regular check-ups over a long period of time, when their health may change.

Ovarian cancer is diagnosed in 7,000 women in the UK each year, but lack of symptoms in the early stages means it is often not discovered until it has spread to other parts of the body. The annual death toll is around 4,600 women.

The latest study by Cancer Research UK scientists provides more evidence of protection against ovarian cancer, which has been recognised in previous research as a major health benefit from using the pill.

It looked at evidence from 45 studies of ovarian cancer in 21 countries, including 23,257 women with ovarian cancer of whom 7,308 (31 per cent) had used oral contraceptives and 87,303 women without ovarian cancer of whom 32,717 (37 per cent) had used oral contraceptives.

Researchers estimated that, in high income countries, using oral contraceptives for ten years cut the risk of developing ovarian cancer before the age of 75 from 12 down to 8 per 1000 women. It reduced the risk of death from ovarian cancer before age 75 from 7 down to 5 per 1000 women.

The reduction in risk did not vary substantially among women taking the pill in the 1960s,1970s or 1980s, suggesting protection does not depend on the type of pill or level of oestrogen it contains.

Professor Valerie Beral, of the Cancer Research UK Epidemiology Unit at Oxford University, said "Worldwide, the Pill has already prevented 200,000 women from developing cancer of the ovary and has prevented 100,000 deaths from the disease.

"More than 100 million women are now taking the Pill, so the number of ovarian cancers prevented will rise over the next few decades to about 30,000 per year."

The Pill also causes long-lasting protection against endometrial cancer (cancer of the lining of the womb).

It causes a short-term increase in breast cancer and in cervical cancer (cancer of the neck of the womb) which, after women stop taking it, reverts within 10 years to the same risk as a woman who has never taken it.

Co-author Sir Richard Peto, Professor of Epidemiology at Oxford University, said "Young women don't have to worry about cancer from taking the Pill because the eventual reduction in ovarian cancer is bigger than any increase in other types of cancer caused by the Pill."

The protective mechanism is probably because women on the pill are not producing any eggs. The normal process of egg release triggers cell damage and repair that raises the risk of tumour development.

Canadian doctors, writing an editorial in The Lancet, say the study is "unequivocal good news" which means the pill should now be made more widely available to women to protect them from ovarian cancer.

It says: "We believe the case is now convincing.

"Women deserve the choice to obtain oral contraceptives over-the-counter, removing a huge and unnecessary barrier to a potentially powerful cancer-preventing agent."

However, Dr Anne Szarewski, Clinical Consultant, Wolfson Institute of Preventive Medicine, London, said a more cautious approach should be adopted despite the pill's good safety record.

She said "Regular check-ups are advisable because women could be taking the pill for 10 years or more.

"Over that period of time they may develop medical contra-indications that were not present when they started taking it, for example they may put on a stone in weight which would increase the risk of DVT."

Julie Bentley, chief executive of the fpa (formerly family planning association) said "This is great news for women as it is further assurance that the contraceptive pill provides lasting protection against ovarian cancer.

"Research has shown time and again that the pill is not only an extremely safe and effective method of contraception but has health benefits other than protecting against unplanned pregnancy.

"There is now substantial evidence showing that for most women the benefits of taking the contraceptive pill are far greater than any of the risks."