Women who take the contraceptive pill for 10 years cut their risk of ovarian cancer by almost half, according to a European study published Wednesday.
Taking the contraception for any length of time also reduces the risk by 15 percent, according to one of the largest studies into the links between diet, lifestyle and cancer.
The study found that 28 in 100,000 women who took the birth control pill for less than 12 months would get ovarian cancer. The risk dropped to 15 per 100,000 for those taking it for 10 years or more.
Getting pregnant is the next best protection against ovarian cancer, reducing the risk by 29 percent. This is reduced by a further eight percent with each child a woman gives birth to.
The research, published in the British Journal of Cancer and co-funded by Cancer Research UK, is part of the ongoing European Prospective Investigation of Cancer (EPIC), based in Lyon, France.
Naomi Allen, a member of the EPIC team based at Oxford University, said, "Ovarian cancer is difficult to detect, and so prevention is key to saving women suffering from this disease. These results are important because most women don't know that taking the pill or getting pregnant can help reduce their risk of ovarian cancer later on in life."
One theory is that taking the pill or getting pregnant changes the level of hormones that can affect a woman's risk of the disease.
However, the researchers warned that the protective effect of the pill must be balanced by an increased risk of breast cancer while using it.