Using national prescribing and cancer registers, they analysed data of nearly 1.9 million Danish women aged 15-49 years between 1995 and 2014.
Women were categorised as never users (no record of being dispensed hormonal contraception), current or recent users (up to one year after stopping use), or former users (more than one year after stopping use) of different hormonal contraceptives.
After taking account of several factors, including age and parity, the researchers found that the number of cases of ovarian cancer was highest in women who had never used hormonal contraception (7.5 per 100,000 women a year), whereas, among women who had used hormonal contraception, the number of cases of ovarian cancer was 3.2 per 100,000 women a year.
There was no firm evidence to suggest any protective effect among women who used progestogen-only products. However, the researchers point out that few women were exclusive users of these products. This limits the ability to detect an effect.
The reduced risk for combined products was seen with nearly all types of ovarian cancer, and there was little evidence of important differences between products containing different types of progestogens.
Based on these figures, the researchers say that hormonal contraception prevented an estimated 21% of ovarian cancers in this group of women. The authors of the study said, "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 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," they conclude.
The findings appeared in the Journal- The BMJ.
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