While the link between hormonal contraception and cancer was discovered years ago, this particular study is the first to examine the risks of more modern formulations of the two popular forms of birth control, reports The New York Times.
The study followed 1.8 million Danish women for more than a decade and found that there was just as much risk in current formulations of birth control as those of decades past. Many doctors hoped and assumed that the modern formulations – which contain lower hormone doses – would be safer to use than their predecessors. "This is the first study with substantial data to show that’s not the case," said David J. Hunter, a professor of epidemiology and medicine at the University of Oxford.
Not only are women using hormonal birth control still 20 percent more likely to get breast cancer than nonusers, but the risk increases the longer a woman uses it.
Still, the risk is still relatively low. The study estimates that hormonal contraception use causes an additional 13 breast cancer cases per year for every 100,000 women using it. So for nonusers, there is an average of 55 cases per 100,000 women, whereas there are 68 for women using hormonal birth control.
This article was originally published on January 22, 2015.
We've seen convoluted research linking birth control to a variety of cancers before. But, a new study is now making the rounds — it suggests that hormonal birth control may increase the risk for developing brain cancer in particular.
The study, published recently in the British Journal of Clinical Pharmacology, looked at data for 317 women with brain cancer (glioma) and 2,126 without collected from Danish health and administrative registries. The women were between 15-49 years old and had a similar number of years of education. The researchers looked at the women's prescription data and categorized them based on how long they had been using hormonal birth control (less than a year, 1-5 years, or over five years) and the type of birth control they were using (progestogen-only or progestogen and estrogen).
The study authors reported that women who had ever used the pill had a "moderately increased risk" for developing brain tumors than those who had never used it, and the risk increased the longer women were on that form of birth control. The risk also went up if the birth control was progestogen-only. The research also showed a heightened risk in those using hormonal intrauterine devices (IUDs), but the risk was lower than for those on the pill.
More than anything else, though, the connection is complicated. Other research linking brain cancer to hormone exposure has turned up weak or contradictory results. But, many of those studies relied on self-reported retrospective data and focused on women over the age of 50. This new study included more young women, and the data was collected through more reliable sources. Still, the study doesn't necessarily suggest a causal link and may be overlooking other potential factors, such as obesity. Previous studies have also linked use of the pill to both increased and decreased risks for developing cancers, including breast, ovarian, and endometrial cancers.
Correction: An earlier version of this article incorrectly stated that women who had ever used the pill had a 40% higher risk for developing brain cancer.