Taking the contraceptive pill could increase the risk of breast cancer more than previously thought, new research suggests.
A study from the University of Michigan has found that some commonly prescribed birth control pills may quadruple levels of synthetic oestrogen and progesterone hormones.
High levels of oestrogen and progesterone can play a part in stimulating some breast cancers to grow, which is why some breast cancer patients are prescribed hormone therapy to block the effect of these hormones on cancer cells.
However, the study authors stressed that the pill has had a positive effect on many women’s lives, so manufacturers need to ensure they’re creating formulations that limit breast cancer risk.
The research found that blood had much higher levels of hormones in women who take birth control pills compared to women who don’t.
The authors examined seven commonly prescribed birth control pills and found that four formulations more than quadruple levels of progestin, a synthetic version of the hormone progesterone.
Another formulation resulted in a 40% higher exposure to ethinyl estradiol, a synthetic version of oestrogen.
The study’s lead author, human evolutionary biologist Beverly Strassmann, stressed that birth control has greatly improved women’s lives.
But, she said, it’s also important to design birth control pills so that they don’t contribute to risk for breast cancer.
“Not enough has changed over the generations of these drugs and given how many people take hormonal birth control worldwide — millions — the pharmaceutical industry shouldn’t rest on its laurels,” she said.
Progesterone and oestrogen are both produced by the ovaries and their levels vary naturally over the course of the menstrual cycle.
The pill replaces these naturally released hormones with synthetic versions.
The study’s goal was to test whether the synthetic versions increased or decreased hormonal exposure compared to what women might get from their own ovaries.
“That this hasn’t been answered is amazing, given that we already know that there’s a correlation between hormonal exposure and breast cancer risk,” Strassmann said.
Strassman’s research pulled data from 12 different studies that measured the amount of oestrogen and progesterone over the menstrual cycle in women who don’t take the pill.
Strassmann and her co-authors then compared the total levels of oestrogen and progesterone in these women to the total levels of synthetic hormones, progestin and estradiol, in women taking one of several commonly prescribed birth control pills for 28 days.
That information was taken from the package inserts for each contraceptive formulation.
The new study follows up Strassmann’s previous research on menstruation and reproductive biology in the Dogon people of Mali, West Africa. Dogon women rarely practice birth control, have an average of nine pregnancies and often breastfeed children to age two years.
Because pregnancy and breastfeeding suppress ovulation, Dogon women have only about 100 menstrual periods during their lifetimes.
That number is a sharp contrast to the 400 periods experienced, on average, by Westernized women who have about two children and seldom breastfeed for more than one year.
“The increased number of menses is associated with increased hormonal exposure and risk for breast cancer,” Strassmann said.
“It is critically important to know whether hormonal contraception further exacerbates this risk.”
Previously commenting on the links between breast cancer and the pill, the NHS said “the baseline risk of women of a fertile age developing breast cancer is small,” so an increase in risk is also fairly small.
It also pointed out “the potential benefits of the pill protecting against other types of cancer, such as ovarian cancer,” adding: “Unfortunately, there are often no easy answers when weighing up the benefits and risk.”
Cancer Research UK currently advises that just “1% of breast cancers in women are due to oral contraceptives”.
“The protective effects of the pill against womb and ovarian cancers last longer than the increased risks of breast and cervical cancers. Overall, this means that the protective effects outweigh the increased risk of cancer if you look at all women who have taken the pill,” it says.
If you’re concerned about the risks associated with your pill, speak to your GP for further information and advice to find the right option for you.