The long-term use of oral contraceptives can reduce the risk of ovarian cancer by almost half, but a late menopause is associated with a higher risk.
Of 327,396 women taking part in the European Prospective Investigation into Cancer and Nutrition, 878 developed ovarian cancer over an average of nine years.
Women who used oral contraceptives for 10 years or more had a 45% lower risk of developing ovarian cancer compared with women who took the pill for a year or less.
The reduced risk for women who had borne children was 29% lower than women who had never given birth, with an 8% reduction in risk for each additional pregnancy.
A high age at menopause was associated with an increased risk of 46% of developing ovarian cancer.
Study author Naomi Allen, an epidemiologist for Cancer Research UK, said: ‘Ovarian cancer is difficult to detect so prevention is key to saving women.'
‘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.'
British Journal of Cancer 2011 105:1436-442