Although modern birth control pills have a lower dose of estrogen than past versions, they are still linked to breast cancer, a new Danish study suggested.
According to the New York Times, older forms of birth control with high doses of estrogen were known to increase the risk of breast cancer in women. However, “many doctors and patients had assumed the newer generation of pills on the market today were safer” because they had lower doses.
But the study found that modern hormonal birth control — including oral contraceptive pills and some types of intrauterine devices, or IUD’s — still increased the risk of breast cancer.
“We did actually expect we would find a smaller increase in risk because today we have lower doses of estrogen in the hormone contraceptives, so it was surprising that we found this association,” Lina S. Mørch, a senior researcher at the University of Copenhagen and the study’s lead author, told the Times.
The study — which followed 1.8 million Danish women for more than a decade — found that users of hormonal contraceptives had 20 percent increase in their relative risk of breast cancer compared to nonusers. Age and the length of time on the pill could increase the relative risk, suggesting a causal relationship.
Researchers estimated that for every 100,000 women, the use of hormonal contraceptives causes an additional 13 cases of breast cancer each year.
“It is a very clear picture for us, very convincing,” Mørch said.
Dr. Øjvind Lidegaard, the paper’s senior author, told the Times, “Nothing is risk-free, and hormonal contraceptives are not an exception to that rule.”
Lidegaard suggested that doctors take time to discuss the risks presented by different types of contraception with their patients, and suggested women reconsider hormonal contraceptives as they age.
Dr. Marisa Weiss, an oncologist who founded the website, breastcancer.org, told the New York Times, “This is an important study because we had no idea how the modern day pills compared to the old-fashioned pills in terms of breast cancer risk, and we didn’t know anything about I.U.D.’s.”
“Gynecologists just assumed that a lower dose of hormone meant a lower risk of cancer. But the same elevated risk is there,” said Weiss, who was not involved in the study. “It’s small but it’s measurable, and if you add up all the millions of women taking the pill, it is a significant public health concern.”
A spokesperson for the American College of Obstetricians and Gynecologists told the Times that they will examine the findings of the study but said hormonal contraceptives are “among the most safe, effective and accessible options available.”