The work is thought to be the largest study of its kind conducted on breast cancer and hormonal contraception such as the combined pill, the progestogen-only pill and non-oral products such as the 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 to women who had never used such contraception.

Researchers found 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 cancers detected during the study period. 

However, the research – carried out by Rigshospitalet, University of Copenhagen, in collaboration with the University of Aberdeen – suggested the numbers affected were likely to be very 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 7,690 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 to disappear five to 10 years after stopping.

Users of progestogen-only contraceptives (mainly pills and the IUS) experienced an increased relative risk of breast cancer.

The study is published in New England Journal of Medicine.