The 20 percent increase in breast cancer risk varied by age and how long the women used hormone-based contraceptives, including pills, contraceptive patches, vaginal rings, progestin-only implants, and injections.
Morch's team pored through years of electronic health records collected by the Danish health system, using prescription data to identify which women had taken the drugs and then track their health outcomes.
These results sound scary at first. Over the years, makers of birth control pills and hormone replacement therapy for women past menopause have reduced the amount of estrogen in their products.
Current and recent use of hormonal contraceptives was associated with a 20 percent increased risk of breast cancer. "But it does show an increased risk, so for people who don't have a great reason for taking oral contraceptives, or are amenable to alternatives, perhaps they should think about it".
On the other hand, among women who used hormonal contraceptives for short periods, the excess risk of breast cancer disappeared rapidly after use was stopped, the researchers said.
Third-generation contraceptive pills are displayed on January 2, 2013, in Lille, in northern France.
Newer formulations of birth control pills appear the carry the same risk of breast cancer as older versions. "In particular the knowledge of risk with newer progestins was sparse".
It's a disappointment to doctors who had hoped that lower doses of hormones in both oral and non-pill contraceptives might be safer than older birth control pills. Dr. Charles A. Leath, a gynecologic oncologist at the University of Alabama at Birmingham, said that while this pathway was plausible, it was far from certain.
North Atlantic Treaty Organisation 'strongly' committed to Georgia's security
The conflict between Ukrainian forces and Russian-backed separatists has claimed more than 10,000 lives since it erupted in 2014. Meanwhile, Tillerson hailed what he called "a productive discussion" with Georgian Foreign Minister Mikheil Janelidze.
"When we look at all comers, the absolute overall increased risk of breast was one extra case of breast cancer for every 7,690 women using hormonal contraception for one year", said Dr. Rebecca Starck, a gynecologist at the Cleveland Clinic. The American Cancer Society says every year it's diagnosed in 200,000 women and a few men, and kills around 40,000. However, it was commonly thought that the newer low-dose estrogen options significantly decreased - or even eliminated - that risk.
"Progestin-only products also increased the risk of breast cancer", Morch noted. "[Contraceptives] also brings benefits, and we should not forget them". "We see from this data that is not the case". Unintended pregnancies cost the USA government $21 billion in 2010, according to a report from the Guttmacher Institute.
Morch and Gaudet noted that breast cancer is relatively uncommon in younger women, so a young woman's overall risk of breast cancer still is low, even if she's taking the pill. "As with any medical intervention, hormonal contraception is associated with specific health risks".
The study shows that "the search for an oral contraceptive that does not elevate the risk of breast cancer needs to continue", said Dr. David Hunter of the University of Oxford in a Journal editorial.
Two types of birth control pills are sold in the US - one that combines synthetic versions of the hormones estrogen and progesterone, and the "minipill" that only delivers progestin, a synthetic formulation of progesterone. "Indeed, some calculations have suggested that the net effect of the use of oral contraceptives for 5 years or longer is a slight reduction in the total risk of cancer", Hunter said.
Duration of use also contributed to associated breast cancer risk.
In Denmark, older women who have completed their families are most likely to use IUDs, including those containing hormones, and they are already more likely to develop breast cancer because of their age, Mørch said.
"No type of hormone contraceptive is risk-free unfortunately", said lead author Lina Morch of Copenhagen University Hospital.