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What Is the Gut-Vagina Axis?
You are probably familiar with the concept of the gut microbiome, and chances are if you’re reading this blog post, you are also familiar with the vaginal microbiome. But what about the link between the two?
While the research is still very much in the early stages, more and more evidence points to connections between the gut microbiome and other organs and body systems — including the brain. It makes perfect sense, then, to think carefully about the connection between the gut microbiome and the vaginal microbiome.
But what do we actually know for sure? There are a few key ideas that the scientific literature is beginning to explore, which this blog post will delve into.
How Antibiotics Reveal the Gut-Vagina Connection
One of the most straightforward ways to understand the link between the vaginal microbiome and the gut microbiome is to consider that anything affecting one part of the body can often unintentionally impact another. Mice studies (1,2) have shown that taking oral antibiotics can result in changes to both the gut and vaginal microbiome composition. While more human data is needed to draw definitive conclusions, it isn’t unreasonable to think that similar effects are likely to occur in humans too.
Beyond the Gut: How the Gut Microbiome Influences the Whole Body
The influence of the gut microbiome expands far beyond the limits of the gastrointestinal tract itself. You may have come across the phrase ‘gut-brain axis’ — which in essence describes how the gut and the brain communicate and interact with each other. The gut microbiome plays a pivotal role in this communication. There is evidence, for example, showing that gut microbiota can trigger the production of important neurotransmitters (3) — chemical messengers that transmit signals throughout your nervous system — including serotonin (the ‘happy’ hormone) and dopamine (the ‘pleasure’ chemical).
In a similar way, the gut microbiome has been shown to influence oestrogen levels, which in turn impacts the vaginal tract and its related microbial community.
The Oestrobolome: How Gut Microbes Regulate Oestrogen Levels
The mechanism behind the gut-vagina axis and oestrogen is a little convoluted, but incredibly interesting. Oestrogen exists in two main forms:
- Conjugated oestrogen — extra molecules are attached, making it easier for oestrogen to move around the body but rendering it biologically inactive
- Unconjugated oestrogen — the attachments are removed, making oestrogen biologically active and able to bind to oestrogen receptors throughout the body
Crucially, some gut microbes are able to convert oestrogen from the conjugated, inactive state into the unconjugated, biologically active state. This has important consequences for the vaginal microbiota — because oestrogen levels can heavily influence the composition of the vaginal microbial community (4). Although not a direct link between the two microbial communities, this highlights just how complex these systems are, and the intricate connections between seemingly unrelated parts of the human body.
Shared Microbial Species: The Gut as a Reservoir?
Because of the physical proximity of the vaginal microbiota and the gastrointestinal microbiota, several microbial species can be commonly identified at both sites. It has been widely believed that the gut microbiota can act as a reservoir for pathogens — particularly when it comes to vulvovaginal candidiasis (VVC), or yeast infections.
Surprisingly, the research suggests this may not be the case. One study examining ‘dual carriage’ of Candida — whether it could be detected in both the gut and vaginal microbiome simultaneously — found this was true for only 5 of the participants (18.5%), and of these, only two (7.4%) had the same Candida species detected at both sites (5).
However, the picture is different for bacteria. Several Lactobacillus strains — including Lactobacillus crispatus and Lactobacillus gasseri — can be identified in both the vaginal and gastrointestinal microbial communities (6), suggesting a meaningful microbial overlap between these two body sites.
What the Gut-Vagina Axis Means for Women’s Health
Overall, there is clearly an undeniable, inextricable link between the gut microbiota and the vaginal microbiota. Our current understanding within scientific literature highlights the inherent complexity of these microbial communities. As research expands, an improved understanding of the gut-vagina axis could provide an opportunity to take a more holistic approach to women’s health — one that considers the body as an interconnected system rather than a collection of isolated parts.
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