The contraceptive pill lowers women's overall risk of cancer, experts say following a major new study in this week's issue of The Lancet. Most noticeably the Pill cuts the risk of ovarian cancer – and has so far prevented 100,000 deaths worldwide from the disease, the researchers say.

The Oxford University team found that the protection against the disease lasted for more than 30 years after women had stopped taking it. They also found that the longer the Pill was used, the greater the protection, and that taking it for 15 years halved the risk of ovarian cancer.

Their survey combined the results of 45 epidemiological studies of ovarian cancer in 21 countries worldwide, involving over 23,000 women. Significantly, it suggests the benefits are sufficient to outweigh the short-lived increase in the risk breast cancer and in cervical cancer (cancer of the neck of the womb).

One of the authors, 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."

In addition, the Pill also causes long-lasting protection against endometrial cancer (cancer or the lining of the womb). Lancet editor Richard Horton said the report showed that the Pill should be made available over the counter.

"We strongly endorse more widespread over-the-counter access to a preventive agent that can not only prevent cancers but also demonstrably save the lives of tens of thousands of women," he said. The Oxford team estimates that, in Western countries, using oral contraceptives for 10 years reduces the risk of developing ovarian cancer before the age of 75 from 12 down to 8 per 1,000 women, and reduces the risk of death from ovarian cancer before age 75 from 7 down to 5 per 1,000 women.

The researchers found that the protection against ovarian cancer did not vary much with different types of the Pill, despite significant reductions in the amount of oestrogen it contained between the 1960s and the 1980s. Lead author Professor Valerie Beral, director 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."

She said that with more than 100 million women now taking the Pill, the number of ovarian cancers prevented worldwide would rise to about 30,000 per year over the next few decades.

Dr Lesley Walker, Cancer Research UK's director of cancer information, said: "All women who have taken the Pill or are currently taking it should be reassured by this study." In the UK 1.2 per cent of women develop ovarian cancer before they are 75 years old. 6,615 women were diagnosed with cancer of the ovary in the UK in 2004. Michael Day