The impact of contraceptives on the microbiota? Hit and miss!

Do hormones in female contraceptives harm the microbiota? According to science, it all depends on the flora in question: the lactobacilli-dominated vaginal microbiota seems to be protected but the gut microbiota is slightly disturbed. 

Created 13 July 2021
Updated 27 October 2021

About this article

Created 13 July 2021
Updated 27 October 2021

All women know that the hormonal fluctuations of the menstrual cycle influence, among other things, the vaginal flora and gut transit. So could female contraceptives, particularly those that work on hormones, modify, for better or worse, the dynamics of the vaginal and gut microbiota?

Oral contraceptives boost the vaginal flora...

The vaginal microbiota has a unique quality: it is in good health when its diversity is low and rod-shaped bacteria, lactobacilli, predominate. This contrasts with other microbiota, including the gut microbiota, which are considered in balance when highly diversified. The predominance of lactobacilli protects the vagina against infection, since lactobacilli release lactic acid (among other substances), which slows the proliferation of pathogens. However, where dominant lactobacilli are replaced by other types of bacteria and the vaginal flora loses its balance (dysbiosis), bacterial vaginosis can result. However, hormonal contraceptives (oral or vaginal) seem to reduce the risk of contracting this disease.1 How? By boosting the lactobacilli! The estrogens contained in these contraceptives result in large quantities of glycogen being deposited on the vaginal walls. Glycogen is the favorite food of lactobacilli and allows the bacteria to multiply and produce more lactic acid. What about other types of contraception? Although research in this area is still limited, the vaginal ring does not seem to cause any substantial modification of the vaginal flora, while IUDs (whether copper or hormonal) appear to have no effect.1

...but slightly disturb the gut microbiota

Unlike the vaginal microbiota, a healthy gut flora should be diverse. However, the pill artificially maintains constant levels of estrogen and progesterone in the blood, which appears to disturb the gut microbiota. In a recent study involving 16 healthy premenopausal women2, oral contraceptives were associated with a minor decrease in gut microbiota diversity and differences in the abundance of several bacterial taxa. However, it is not yet known whether the hormones in the pill have a direct effect on the gut microbiota or whether they work indirectly via other physiological processes that themselves affect the bacteria in the gut. Despite this, these preliminary results show that the pill may affect women’s health. Hence the need for further studies to gain a more complete understanding of the impact of these drugs on the gut microbiota.

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