Common IUD birth control devices may raise the risk of breast cancer, research suggests.
Women who used hormonal IUDs which slowly release the contraceptive levonorgestrel were 40 percent more likely to be diagnosed with the disease within at least five years than women on other forms of birth control.
Among women who used them for over a decade, the risk went up to 80 percent.
About one in five sexually active women in the US and one in six in the UK use IUDs, which are inserted into the uterus by a doctor and last anywhere from three to eight years. Many women opt for these so they don’t have to remember to take a pill every day.
The researchers noted that while the overall risk is low, since IUDs are used long term, ‘information about breast cancer risk should accompany discussions about benefits and risks’.
Researchers in Denmark found that using a hormonal IUD may raise the risk of breast cancer by 40 percent
The above graph indicates how breast cancer rates have risen by one percent every year across all age groups but slightly faster among women under 50 years old
Experts suggest that this may be due to the influx of hormones like estrogen and progesterone binding to proteins in the breasts and fueling certain forms of cancer.
They may also be riskier than pills or other forms of birth control because they are used for years at a time, sometimes up to a decade.
A preview of the new research was published Monday in JAMA. However, the full study has not yet been released.
The team from the Danish Cancer Institute evaluated 157,190 girls and women ages 15 to 49 from 2000 to 2019. The average participant age was 38.
Half of the participants were prescribed a hormonal IUD using levonorgestrel, the same drug found in the morning-after pill, while the other half either used other forms of birth control or no contraceptive.
In the US, levonorgestrel is used in Kyleena, Liletta, Mirena, and Skyla IUDs.
Participants were also broken into groups based on how long they used the IUDs: zero to five years, five to 10 years, and 10 to 15 years.
The researchers found that on average, hormonal IUDs led to a 40 percent increased risk of breast cancer compared to other forms of birth control.
Those who used this form of birth control were at a 30 percent increased risk after zero to five years and 40 percent for five to 10 years.
The likelihood was greatest for the long-term group, as women who used hormonal IUDs were 80 percent more likely to develop breast cancer after 10 to 15 years of use compared to those on other contraceptives.
The team noted that the risk of breast cancer contraceptive pills was about 20 percent.
The researchers did not explain why hormonal IUDs may increase breast cancer risk, though experts have suggested that the influx of hormones like progesterone and estrogen may stimulate the growth of cancer cells in some forms of breast cancer.
These hormone-sensitive cancers include estrogen receptor positive (ER positive) and progesterone receptor positive (PR positive) breast cancers, which contain proteins that bind to hormones and trigger cancer cell growth.
While the findings appear grim, Professor Amy Berrington, a professor of clinical cancer epidemiology at the Institute of Cancer Research in the UK who was not involved in the study, said: ‘it is a small risk that should be considered along with the benefits from the contraceptive.
‘The risk is likely even smaller for younger women because their risk of breast cancer is even lower.’
There were several limitations to the research. The study looked at correlation rather than causation, and full results have not been released.
It’s also unclear which forms of breast cancer the women were diagnosed with.
The findings come as breast cancer surges in American women under 50, which experts have suggested could be due to changes in reproductive habits like women having children later or starting menstruation earlier.
About 310,000 women will be diagnosed with breast cancer this year, the American Cancer Society estimates, and around 42,000 will die.