Low-dose contraceptive protects against cancer

A Danish study involving almost two million women has found that low-dose oestrogen contraceptive pills are associated with a reduced rate of ovarian cancer.

The news will come as a relief to users and clinicians alike. The protective effect against cancer of oral contraceptives has long been established, but most studies in the field used data arising from older-style pills, which contained comparatively high doses of oestrogen.

Over the past few years, contraceptive pill manufacturers have switched to a new formula, with different progestogens and much lower levels of oestrogen. This gave rise to the not unreasonable speculation that the reduced quantity might also lessen the protective anti-cancer effect.

Now, however, the latest study, by researchers led by Lisa Iversen from the University of Aberdeen in Scotland, dispels the concern.{%recommended 2143%}

The researchers used Danish prescribing and cancer registries to track the health of 1.9 million women aged between 15 and 49 for the years 1995 to 2014. They divided the women into three categories: those who had never used oral contraceptives, those who were using the pills or had stopped within the past 12 months, and those who had stopped for longer than a year.

After taking into account other potential influences, they found that the rate of ovarian cancer among women who had never used the contraceptives was 7.5 per 100,000 – more than double that found in the other two cohorts.

There was no evidence of a similar protective effect among women who used progestogen-only pills, but that might because this group comprised only 14% of the sample and was thus too small to produce meaningful results.

The study was observational, so cannot be used to draw any conclusions regarding the mechanics of the protective effect. Nevertheless, Iverson and her colleagues conclude that oral contraceptives prevented an estimated 21% of cancer cases among the user groups.

“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,” say the authors.

“The reduced risk seems to persist after stopping use, although the duration of benefit is uncertain. Presently, there is insufficient evidence to suggest similar protection among exclusive users of progestogen-only products.” 

The study is published in the journal The BMJ.