New research has added to the growing pile of evidence that taking hormonal contraceptives increases your relative risk of developing breast cancer.
While these findings fall in line with what we already know, the study focussed mostly on formulations and delivery methods that have been developed since the mid-1990s - meaning that even newer contraceptives on the market are still adding to the problem.
The study was conducted by researchers from the University of Copenhagen on data collected from nearly 1.8 million Danish women between the ages of 15 and 50.
The data was taken from the National Register of Medicinal Product Statistics, tracking on average just under 11 years of the women's lives since 1995 and including details on over 11,500 cases of breast cancer.
This is big data, so the results aren't to be taken lightly. But it is vital that we take them in perspective.
For those who had been taking some form of hormonal contraceptive – whether orally, via an implant, patch, IUD, or vaginal ring – the risk of getting breast cancer was comparatively increased.
This risk depends on the amount of time they'd been taking the contraceptive. If it was less than a year, the increase was roughly 9 percent. For more than a decade, it was 38 percent.
Interestingly, for those on hormonal contraception for more than 5 years, a small but significant risk remained after discontinuing its use.
Previous studies had found no such persistence in risks, highlighting a need for further investigation.
This study stands out not only for its large sample size, but also for the fact that the huge sample size allowed the team to compare various formulations of hormonal birth control.
While there are some subtle differences, taken together the research suggests that even newer generations of hormone-based contraception, such as progestin-based implants, can raise the risk of breast cancer.
What does all of this mean, though? An increased risk of 38 percent can look terrifying, but it's important to keep in mind that the overall risk of breast cancer among women – while high compared to most cancers – is still relatively rare in younger women.
In an editorial on the study, David Hunter from the Nuffield Department of Population Health put the results into perspective.
"First, the approximately 20 percent higher risk of breast cancer among women who currently use hormonal contraceptives and those who do not must be placed in the context of the low incidence rates of breast cancer among younger women," Hunter writes.
Among those under the age of 35, taking a hormonal contraceptive for less than one year added just one new breast cancer case for every 50,000 women.
There are other risk factors to consider as well, including age and family history. The study did its best to take into account things like pregnancy and inherited risks, but didn't include factors such as physical activity.
The influence of a history of taking such contraception also seems to become less significant among post-menopausal women aged between 50 and 70, where the risk of getting breast cancer peaks.
Hunter adds that in contrast to an increased risk of breast cancer, oral contraceptives do lower the chances of developing other diseases later in life.
"Beyond the fact that they provide an effective means of contraception and may benefit women with dysmenorrhea or menorrhagia, the use of oral contraceptives is associated with substantial reductions in the risks of ovarian, endometrial, and colorectal cancers later in life," says Hunter.
Better still, the benefits stick around for decades after you stop taking contraception, unlike the risks which tail off far more quickly.
For the rest of us, the results should factor into decision making, but not cause alarm. As usual, talk to your doctor if you're concerned.
This research was published in The New England Journal of Medicine.