Women who took oral contraceptives for at least 10 years were 45% less likely to develop the disease, international research led by a team at Oxford University showed.
What did researchers investigate?
It is already known that oral contraceptives can reduce the risk of ovarian cancer.
Researchers working on the European Prospective Investigation of Cancer (EPIC) study wanted to look the effect on this risk of reproductive factors, such as breastfeeding.
They analysed the records of 327,396 women from across Europe, incorporating into the analysis a variety of lifestyle and health factors such as BMI, hysterectomy, number of pregnancies and duration of oral contraceptive use.
What did they find?
Researchers discovered that women who took oral contraceptives at any stage were 14% less likely to develop ovarian cancer than women who did not.
Over nine years of the study, 272 women developed ovarian cancer out of 100,000 who used oral contraceptives for one year or less.
In contrast, this rate was just 157 among women using oral contraceptives for 10 years or more – a 45% reduction in risk after adjustment.
Newspaper reports cited figures of 28 ovarian cancer cases per 100,000 among women using oral contraceptives for one year of less and 15 cases for those who used them for 10 years or more.
These figures were taken from a press release by Cancer Research UK, who provided funding for the EPIC study.
The research also showed that giving birth had a protective effect, but that breastfeeding did not give any additional protective effect.
Are the results important?
Dr Naomi Allen, a Cancer Research UK epidemiologist, who works on the EPIC study, 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, said: ‘These days it is not uncommon for women to have fewer children or none at all.
‘Women tend to be unaware that these reproductive factors have a protective effect on their risk of ovarian cancer.’
Dr Richard Edmondson, women's cancer expert at the University of Newcastle, said any benefits must be balanced against a slight increased risk of breast cancer, revealed in earlier studies.
‘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.’