A new, large-scale study published in The BMJ suggests that newer birth control pills can significantly reduce the risk of ovarian cancer among young women.
In 2014, for instance, over 21,000 new cases of ovarian cancer occurred, at least 14,000 of which resulted in death.
Previous research has suggested that combined oral contraceptives — that is, birth control pills that contain both estrogen and progestogen — may lower the risk of ovarian cancer in women of reproductive age.
Moreover, these beneficial effects lasted for years after the women discontinued them, noted the studies.
However, these past results applied to older contraceptives that had higher amounts of estrogen and contained older forms of progestogen. Little was known about the effects of newer pills.
New research aimed to fill this knowledge gap by studying the effects of newer birth control pills on the risk of ovarian cancer.
Lisa Iversen, a research fellow with the Institute of Applied Health Sciences at the University of Aberdeen in the United Kingdom, led the new study. She is also the corresponding author of the paper.
Studying contraceptives and ovarian cancer
Iversen and colleagues examined data available on almost 1.9 million Danish women who were between 15 and 49 years old.
The researchers looked at several Danish national databases and investigated the effect of both combined and progestogen-only hormonal contraceptives.
The women were grouped into "never users" — that is, women who had not been prescribed any hormonal contraception — "current or recent users" — describing women who were either taking birth control pills or had stopped taking them up to 1 year prior — and, finally, "former users" — that is, women who had discontinued use more than 1 year prior to the study.
Approximately 86 percent of the oral contraceptives that the women used were combined pills.
The researchers accounted for factors such as the women's age and the number of times they had been pregnant; they also applied the so-called Poisson regression model to statistically analyze the risk of ovarian cancer among the different groups.
Pills prevented 21 percent of ovarian cancers
The researchers concluded that women who had never used hormonal contraceptives had the highest incidence of ovarian cancer.
Specifically, the researchers found 7.5 cases per 100,000 person-years among the women who had never used birth control pills, whereas in the remaining groups of women, the incidence was 3.2 per 100,000 person-years.
This means, the authors explain, that the "use of hormonal contraception prevented 21 [percent] of ovarian cancers in the study population."
Iversen and colleagues explain, "Use of contemporary combined hormonal contraceptives is associated with a reduction in ovarian cancer risk in women of reproductive age — an effect related to duration of use, which diminishes after stopping use." They add:
"Based on our results, contemporary combined hormonal contraceptives are still associated with a reduced risk of ovarian cancer in women of reproductive age, with patterns similar to those seen with older combined oral products."
The researchers did not find any significant evidence of differences between contraception brands, nor were they able to establish if progestogen-only pills had the same beneficial effects.
"[T]here is insufficient evidence to suggest similar protection among exclusive users of progestogen-only products," the authors write.
Iversen and colleagues also caution that this study cannot establish causality. However, they highlight the fact that the results support previous research on older birth control pills.
Oral contraceptives remain very popular across the world and in the U.S. Estimates from 2014 show that over 9,500,000 women of reproductive age have used the pill in the last month.