The Deep-Dive Series: The Vaginal Microbiome
- August 2, 2018
The human vagina plays host to a community of microorganisms, termed as ‘the vaginal microbiome’. They, like all the other microorganisms that live in and on us, share a mutually beneficial relationship with us. In fact, the health of the vagina, vulva and cervix is heavily dependent on these microorganisms.
Here’s a look at their role in vaginal health, what disturbs their populations and how we can maintain a healthy environment for them.
The composition and role of the vaginal microbiome
The vaginal ecosystem is dominated by a species of bacteria from the genus ‘Lactobacilli’.
This appears to be unique to humans; they make up 70% of the human vaginal microbiome, while they feature in only 1% of the vaginal microbiome of other mammals. There are many theories that propose to explain this, ranging from our distinct reproductive physiology, to a high risk of contracting STDs.
Regardless of the reason, the composition of our vaginal microbiome plays many important roles.
1] It maintains the pH balance
Lactobacilli produce lactic acid, which keeps the vaginal pH at an acidic environment of about 3.5 to 4.5. This is believed to protect women from sexually transmitted pathogens as well as infections that could arise from symbiotic microbes that become pathogenic when in high numbers.
Interestingly, Lactobacilli have long been believed to primarily feature in vaginal communities- but recent studies show that about 20 to 30% of women don’t have them in very high numbers, and are still perfectly healthy. Instead, these women have a diverse range of other bacteria genera (plural of ‘genus’, which is one step above ‘species’) that are also capable of maintaining an acidic environment. This discovery could very well redefine what a “healthy” vaginal microbiome means.
2] It produces antimicrobial compounds
Lactobacillus also produce other compounds apart from lactic acid, like ‘defensins’ and ‘hydrogen peroxides’, which are antimicrobial. Defensins are a class of antimicrobial compounds that act against specific strains of bacteria and viruses. Hydrogen peroxide, on the other hand, kills off many species; in effect, it can both kill pathogens and even prevent species of good bacteria from overgrowing and creating problems.
3] It helps regulate host defence mechanisms
As part of our immune system, mucous membranes line all the openings in the body (for example, in the nostrils) and act as a barrier against pathogens. Mucous membranes are also present in the vagina; the vaginal microbes that colonise them keep these membranes healthy, in turn promoting the immune system.
When the antimicrobial compounds produced by the Lactobacilli (like defensins) are overpowered by potentially infectious agents, it triggers an immune response, which results in inflammation around the area. Lactobacilli also help reduce inflammation once the threat has been addressed, thereby regulating our immune system.
4] It provides a suitable environment for fertilisation and implantation
During pregnancy, fewer numbers of Lactobacillus in a vaginal microbiome is associated with adverse birth outcomes, particularly preterm birth and infections.
5] It populates or contributes to the microbiome of the child
During childbirth, women pass a significant population of microbes onto the infant when it passes through the birthing canal. This continues to pass to the child through skin-to-skin contact and breastfeeding, forming a microbiome that matures as the child grows.
Dysbiosis of the vaginal microbiome
When certain microbes living in the vaginal ecosystem grow beyond a threshold, they become opportunistic. This disequilibrium in microbe populations is known as ‘dysbiosis’.
Our own behaviour constantly disrupts the vaginal ecosystem. Using antibiotics, hormonal contraceptives (and other methods of birth control), sexual activity, vaginal lubricants and douching are all examples of human behaviour that results in dysbiosis.
A dysbiosis may create issues for a long time, without actually leading to a full-blown infection. It may also increase our risk of infections from pathogens that are transmitted sexually or through our surroundings. There are two main categories of infections:
1] Bacterial infections
Bacterial vaginosis (BV) is a vaginal infection caused by the overgrowth of opportunistic bacteria. It’s the most common cause of vaginal discharge in (reproductive) women. BV is linked to lowered numbers of Lactobacilli and a pH with relatively low acidity (above 4.5). It’s also associated with infertility, preterm birth, maternal infections, and the increased risk of sexually transmitted diseases.
A thick layer of bacteria, called a ‘biofilm’, is the hallmark of bacterial vaginosis. Neither our immune system nor antibiotics can fully destroy biofilms, because of which these infections tend to persist and have a high rate of relapse and recurrence.
2] Fungal/yeast infections
Although fungi are vastly outnumbered by their bacterial counterparts in the vaginal microbiome, they’re still important constituents of the vaginal ecosystem in many healthy women.
Candida albicans helps the environment in many ways, liking aiding Lactibacillus in their anti-inflammatory response covered earlier. However, it’s also the leading cause of yeast infections in women, because it can easily become pathogenic; so much so that 3 out of 4 women get it at some point in their life.
What triggers the transition from a commensal (long-term, symbiotic) yeast to a pathogenic one is still unclear. However, we know that these infections generally occur when an individual’s immunity is compromised, if there are breaches in the vagina’s epithelium (the cells lining the vaginal wall), or when there’s dysbiosis.
Factors that keep the vaginal microbiome healthy
We know that our behaviour can cause dysbiosis in the vaginal microbiome. Conversely, we can also do things that nurture the vaginal ecosystem.
1] Maintaining a high acidity environment and our glycogen levels
Glycogen is a form of glucose stored in the body, as a fuel source. When the cells lining the vaginal epithelium contain glycogen, glycogen gets broken down into glucose and feeds Lactobacillus, increasing their population.
The thickness of this epithelium, and the amount of glycogen in it, depends on an individual’s levels of oestrogen, the female sex hormone. The higher the oestrogen, the thicker the epithelium. Consequently, Lactobacilli are most abundant and the vaginal pH most acidic when oestrogen levels peak right before ovulation. That’s also how contraception pills affect our microbiome- but whether it improves it or is detrimental depends on the formulation of the pill.
However, when there’s dysbiosis in the vaginal microbiome, glycogen can overfeed the bacteria as well as fungi in the vaginal ecosystem – this can create problems.
Knowing this, we can help maintain the ecosystem by:
i] Eating plenty of dietary fibre
Fibre prevents the sudden spike in blood glucose when we consume carbohydrates. Since glucose is converted to glycogen, eating plenty of fibre prevents excess production of glycogen.
Fibre even feeds the gut’s good bacteria, when then release short-chain fatty acids like acetate, propionate, and butyrate (which, incidentally, is also present in ghee). These fatty acids help prevent infections and reduce inflammation in the body, and in the vaginal microbiome, even help prevent Candida albicans from turning pathogenic.
ii] Managing our stress levels
Cortisol, the stress hormone, stops glycogen from accumulating in the epithelium, which reduces the numbers of Lactobacillus.
Noradrenaline, another hormone released when we’re stress, increases inflammation in the vaginal tissue. When unnecessary, excess inflammation can damage the microbiome by recruiting immune cells that attack all microorganisms in the area- good and bad.
By managing our stress levels, we can help reduce the effects of these stress hormones.
2] Consuming probiotics
It’s a widely held belief that, when orally consumed, the good bacteria in probiotics make their way to the vaginal tract. This would mean that the microbiome in the gut and vagina can help each other.
Eating foods like yogurt and kefir or even supplementing with probiotics is a good way to help populate vaginal walls with good bacteria. A gynaecologist may even recommend the use of introducing probiotics to the vagina through applicators.
3] Eating phytonutrient-rich foods
Phytonutrients are plant-based compounds that benefit our health. Some of them even have antibacterial properties, which means that can help supress the overgrowth of commensal microbes while even reducing pathogenic ones.
Certain phytonutrients in cranberry juice, in particular, block the critical first step in bacterial infections: the ability of bacteria to stick to surfaces and form biofilms. However, it’s worth noting that cranberry may prevent these infections from occurring but won’t be able to treat one.
Even honey, tea tree, turmeric and garlic are generally consumed as a way to promote vaginal health.
While eating these foods is a good idea in general, it would be best to see a gynaecologist if you experience symptoms of infection.
4] Staying protected and maintaining hygiene
The microflora of the human vagina has been meticulously scrutinised for over a hundred years. Yet, none of this information has made its way to our treatments of common vaginal disorders- even today. Instead of turning to methods that kill both commensal and pathogenic microorganisms (thereby promoting dysbiosis), it’s time to focus on maintaining our symbiotic relationship with microbes. The good news: slowly, but surely, we are heading that way.
Brooks JP, et al. Contraception 2017 Apr; 95(4): 405-413.
Doyle R, et al. Appl Environ Microbiol March 2018; 6(84): e02150-17.
Janeway CA Jr, et al. Immunobiology: The Immune System in Health and Disease. 5th edition. New York: Garland Science; 2001. The mucosal immune system. Available from: https://www.ncbi.nlm.nih.gov/books/NBK27169/
Ma B, et al. Annu Rev Microbiol 2012; 66: 371-389.
Machado D, et al. Front Microbiol 2015; 6: 1528.
Mei J, et al. Int Food Res J 2010; 17: 557-561.
Miller EA, et al. Front Microbiol 2016; 7: 1936.
Mirmonsef P, et al. PLoS One. 2014; 9(7): e102467.
Park YJ and Lee HK. Front Immunol 2018 Jan 10; 8: 1955.