Women who take the Pill for 10 years almost halve their risk of ovarian cancer, according to a study.But experts say this must be balanced against the risk of breast cancer, which is higher in women on the Pill.
For every 100,000 women on the Pill for 10 years there are 50 extra breast cancers and 12 fewer ovarian cancers, data shows.
The study is published in the British Journal of Cancer.
It adds weight to previous research suggesting factors like the Pill and pregnancy can impact on cancer risk by changing the level of hormones in the body.
Dr Richard Edmondson of the Northern Institute for Cancer Research at the University of Newcastle, said: "Women may be reassured to know that the oral contraceptive is not only an effective contraceptive but can have the added benefit of reducing their risk of ovarian cancer.
“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”End Quote Naomi Allen University of Oxford
"This is however balanced against a slightly increased risk of developing breast cancer."To put this in context, it is estimated that if 100,000 women use the Pill for 10 years or more, there will be 50 more breast cancers than would have otherwise occurred, but 12 fewer ovarian cancers.
"This may be particularly important for women with an increased risk of ovarian cancer in their family."
Large study The study followed more than 300,000 women enrolled in a large European study known as EPIC (European Prospective Investigation of Cancer).
The women were taking the combined oral contraceptive pill, which contains two hormones, an oestrogen and a progestogen.
Researchers say they found evidence that taking the Pill for 10 years reduced the risk of ovarian cancer by almost half, compared with women who had used the contraceptive for a year or less.
- There were about 28 ovarian cancer cases per 100,000 women who used the Pill for a year or less
- There were about 15 ovarian cancer cases per 100,000 women who took the Pill for at least 10 years
- Among women who have never been pregnant, there were 34 ovarian cancer cases per 100,000 women
- Among women who have gone through pregnancy at least once there were 24 ovarian cancer cases per 100,000 women
The team also say it found evidence that having a baby reduced the risk of ovarian cancer; the more children a woman had, the bigger the protection.However, they add that their research did not find evidence of a link between breastfeeding and protection against ovarian cancer, which has been found in some other studies.
Ovarian cancer is the fifth most common cancer in women in the UK, with more than 6,500 cases diagnosed each year. Several factors are known to play a role including age, faults in certain genes, obesity and smoking.
Danger signs Naomi Allen is an epidemiologist for Cancer Research UK at the University of Oxford who works on the EPIC study.
She 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."
Sara Hiom, director of health information at Cancer Research UK, added: "Treatment for ovarian cancer is better if the disease is caught as early as possible.
"So all women should be aware of the signs of ovarian cancer like pain in the lower tummy, bloating, increased tummy size, difficulty eating or feeling full.
"If these symptoms are new and happen on most days then it's worth getting checked out by your doctor without delay."
Meanwhile a separate study, published in the British Medical Journal, appears to confirm earlier research that suggested that some newer types of contraceptive pill are more likely to cause blood clots.
Researchers at the University of Copenhagen, Denmark, said women on pills containing drospirenone, desogestrel or gestodene had double the risk of clots compared with an older drug, levonorgestrel.