The researchers found that the protection against ovarian cancer lasted for more than 30 years after women had stopped taking the Pill. They also found that the longer the Pill was used the greater the protection and that taking the Pill for 15 years halved the risk of ovarian cancer.
Researchers estimated that, in high income countries, using oral contraceptives for ten years reduces the risk of developing ovarian cancer before the age of 75 from 12 down to 8 per 1000 women, and reduces the risk of death from ovarian cancer before age 75 from 7 down to 5 per 1000 women.
The new report brings together worldwide evidence from 45 epidemiological studies of ovarian cancer in 21 countries. These include 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.
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. 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 or the lining of the womb) but causes a short-lived increase in breast cancer and in cervical cancer (cancer of the neck of the womb). 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."
Young women take the Pill mostly for contraceptive purposes. There are known to be some definite health risks among current or recent users. However, these are outweighed by the long-term protective effects against the devastation of ovarian cancer - one of the most dangerous types of cancer.
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. Any woman with concerns about taking the contraceptive Pill should discuss them with her GP or local Family Planning Clinic."
