Women who currently use hormonal contraceptives have a 20 per cent higher risk of breast cancer than those who do not use them, according to new research.
The work is said to be the largest study of its kind ever conducted on breast cancer and hormonal contraception such as the combined pill, the progestogen-only pill and non-oral products such as the hormone-intrauterine system (IUS).
It followed 1.8 million Danish women aged under 50 from 1995 to 2012 to assess breast cancer risk in users of different types of hormonal contraception as compared with women who had never used hormonal contraception.
Researchers found that in current and recent users of any type of hormonal contraception, the risk of breast cancer was 20 per cent higher, with 11,517 new breast cancers detected during the study period.
The research was carried out by Rigshospitalet, University of Copenhagen, in collaboration with the University of Aberdeen.
However, the study suggested the numbers affected were likely to be low.
Professor Phil Hannaford, who led the research team based in Aberdeen, said: "Breast cancer is rare in young women.
"In this study, the absolute extra risk of breast cancer associated with use of hormonal contraception among all women age 15-49 was 1.3 per 10,000 person-years, or one extra breast cancer for every 7690 women using hormonal contraception for one year."
The study found little evidence of consistent differences in risk between users of combined oral contraceptives with different progestogens.
Researchers did not detect an increased risk in former users who had used hormonal contraception for less than five years while the increased risk in long-term users gradually decreased by time and disappeared five to 10 years after stopping.
Users of progestogen-only contraceptives (mainly pills and the IUS) experienced an increased relative risk of breast cancer.
Prof Hannaford also pointed to research published earlier this year and said the two studies suggest that today's pills have similar cancer risks and benefits as older preparations.
"The study found an increased risk of breast and cervical cancer in current and recent pill users, risks which disappeared within approximately five years of stopping oral contraception," he said.
"Importantly, the study also found that women who had ever used the pill were less likely to have colorectal, endometrial or ovarian cancer than women who had never used the pill - benefits that persisted for many years after stopping the pill, perhaps 30 or more years."
The study is published in New England Journal of Medicine.
