If you search for information about gut health and polycystic ovary syndrome (PCOS), or vaginal probiotics and bacterial vaginosis (BV), you’re sure to come across some very convincing marketing claims.
Researchers are paying more attention to half of the world’s population by studying the links between gut and vaginal microbes and female health. But can your microbes really explain what’s happening in your body?
In this article, we look at the evidence on how microbes and hormones interact in PCOS, endometriosis, pregnancy and after childbirth. We also explore the vaginal microbiome and common conditions such as thrush and BV, and explain how to weigh up the evidence when making everyday decisions.
If you’re interested in gut health and menopause, you’ll find links to further reading at the end.
How hormones and microbes interact
Your body hosts trillions of microbes, which have evolved alongside humans over millennia. Most of them live in your gut, and together they’re called your gut microbiome.
But you also have a skin microbiome, an oral microbiome and, if you have a vagina, a vaginal microbiome.
Some of your gut microbes are involved in oestrogen metabolism. Researchers call this group of microbes the ‘estrobolome’.
Your body has natural processes that maintain the balance of your hormones. To do this, your liver deactivates circulating oestrogen, and it’s excreted through the gut.
The microbes in the estrobolome produce an enzyme that can reverse this deactivation, which allows some oestrogen to re-enter your circulation. This is also part of your body’s system of maintaining hormone balance.
A healthy gut microbiome is usually very ‘diverse’, meaning it contains lots of different microbes. When diversity is lower or the ratios of the different microbes are out of balance, it’s called dysbiosis.
Researchers have suggested that dysbiosis is linked with lower levels of oestrogen, particularly after menopause.
However, it’s important to remember that most of your oestrogen is made in the ovaries if you’re female. It’s not yet clear how big a role oestrogen that re-enters from your gut plays, and much of the research comes from animal studies.
PCOS and the gut microbiome
PCOS, which has been formally renamed polyendocrine metabolic ovarian syndrome (PMOS), is a condition that affects hormone levels. This includes the hormones that regulate how the ovaries work, but also others that regulate your metabolism, mood and skin.
Researchers have identified differences in the gut microbiomes of women with PCOS.
There’s no good-quality evidence yet that these differences cause PCOS symptoms. However, there’s some emerging evidence that probiotics might help improve some PCOS health markers.
Some researchers have suggested that dysbiosis plays a role in PCOS, and women with the condition may also be more likely to experience irritable bowel syndrome (IBS). However, this isn’t an established fact in any medical guidelines at the moment.
A 2023 systematic review and meta-analysis of 28 studies found less diverse gut microbiomes and more dysbiosis in women with PCOS than in women without it.
By contrast, a 2024 analysis of 14 studies found no difference in gut microbiome diversity, but did report that certain species were characteristic of PCOS.
How these changes in the gut microbiome might be linked with symptoms and health outcomes of PCOS still isn’t clear.
Scientists have also started looking at whether probiotics could help. Several systematic reviews and meta analyses have linked probiotics with lower insulin resistance and improvements in other clinical measures of PCOS.
But this research is still at an early stage, so the results should be treated with caution, while scientists continue to look at links between PCOS and the gut microbiome.
Endometriosis and digestive symptoms
Endometriosis is a health condition where tissue similar to the lining of the womb grows outside the uterus, often causing pelvic pain, painful periods and issues with fertility.
‘Endo belly’ is a common name for cyclical bloating that some people with endometriosis experience, particularly in the second half of their menstrual cycle. It’s an informal term and doesn’t mean that endometriosis is a gut health condition.
Some women with endometriosis also have gastrointestinal symptoms, such as diarrhoea, constipation, wind and pain when pooing. These symptoms are often cyclical and can resemble IBS, which can lead to misdiagnosis or delays in diagnosis.
Researchers have started looking for links between endometriosis and the gut and vaginal microbiomes, but the evidence so far is very limited. Some studies have found differences in certain bacteria between women with and without the condition.
But there’s no good-quality evidence yet linking these differences to specific symptoms, or showing that changing the microbiome would ease any symptoms, including endo belly.
If you have persistent or disruptive cyclical digestive symptoms, particularly alongside pelvic pain or painful periods, it’s important to speak with your doctor.
The microbiome around pregnancy and after childbirth
There’s evidence that the gut microbiome changes during pregnancy, but less is known about what happens after childbirth and what this may mean for postpartum recovery.
Progesterone levels rise throughout pregnancy, which researchers have linked with increases in bifidobacteria. These bacteria help break down sugars in breast milk.
Some research suggests that changes in the maternal gut microbiome during pregnancy may influence the microbes transferred to the baby and may help with training the newborn’s immune system. However, how this works and how much it matters are still being investigated.
Other studies have found no differences in the gut microbiome throughout pregnancy and after childbirth. Postpartum recovery depends on many factors, including the type of birth and your medical history.
If you're considering a probiotic while breastfeeding, check that the specific product has appropriate safety information for use during this time. If you're unsure, speak to your pharmacist, midwife or doctor.
Constipation is very common during pregnancy and after birth. Your midwife or doctor can advise you, and you can read more in our guide to constipation relief at home.
The vaginal microbiome and intimate health
A healthy vaginal microbiome contains mostly Lactobacillus species. These microbes play a critical role in preventing vaginal infections by producing lactic acid, which keeps the vagina acidic. They also support the local immune system and make hydrogen peroxide and other antimicrobial compounds.
Most women have a Lactobacillus-dominant vaginal microbiome. One species, Lactobacillus crispatus, has been linked with a vaginal microbiome that’s less prone to infections.
A vaginal microbiome dominated by Lactobacillus species is generally associated with vaginal health. These bacteria may contribute to protection against some infections, such as BV, sexually transmitted infections and diseases of the reproductive tract.
However, some women have a more diverse vaginal microbiome that isn’t dominated by Lactobacillus, without any health consequences.
Is it BV or thrush?
BV and thrush can cause similar symptoms, but they aren’t the same condition.
BV is caused by an imbalance in your vaginal microbiome when levels of Lactobacilli drop and other bacteria take over. The main symptom is a change in vaginal discharge. It can become thin and grey or white, with a fishy smell that may be stronger after sex.
Usually, BV doesn’t cause itching or soreness, and around half of people with it have no symptoms. It can be treated with antibiotic tablets, gels or creams.
Thrush is caused by an overgrowth of a yeast called Candida, which is normally harmless. The main symptoms are a white, odourless discharge and itching or irritation around the vulva and vagina. You may also have soreness or stinging during sex or when you pee.
Thrush can be treated with antifungal tablets, creams or pessaries.
It’s best to see a doctor if you’re unsure whether your symptoms are due to BV or thrush.
Can probiotics help with vaginal health?
For BV, there’s some evidence that specific probiotics used after antibiotics can reduce the risk of the infection coming back.
In one clinical trial, BV came back in 45% of trial participants who had used only antibiotics, compared with 30% of participants who had used a strain of L. crispatus administered into the vagina after antibiotics.
However, these findings can’t be applied to probiotics generally, and further research is needed to establish which strains, doses and routes are effective.
A 2022 systematic review and meta-analysis of 20 clinical trials that had tested various probiotics for BV concluded that probiotics may help with treatment, but the researchers highlighted the need for stronger evidence.
For thrush, there currently isn’t any good-quality evidence that probiotics can help.
A 2017 systematic review of 10 clinical trials found that taking probiotics alongside antifungal medicine was linked with faster recovery, but the authors concluded that the quality of the evidence was too low to be certain.
What the evidence means for everyday decisions
Your gut and vaginal microbiomes both play a big part in your overall health. Your gut microbiome supports digestion and immunity. It also allows the gut and the brain to communicate via the gut-brain axis.
Your vaginal microbiome helps keep infections at bay and supports your immune system.
If you’re thinking about taking probiotics, check the evidence for the specific product by asking these questions:
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Was it studied in people like me? If the evidence comes only from animal studies, or from people in a very different situation from yours, the results may not apply to you.
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Was the same product used in the same way? The evidence should make clear what was tested. An oral probiotic and a vaginal one aren’t interchangeable, and a strain that helps with BV won’t necessarily help with PCOS or endometriosis.
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Did it improve something that matters? What’s important depends on the condition you want to address. Lower insulin resistance is useful if you have PCOS, but it isn’t relevant to BV.
There are many other ways to support your gut health and vaginal health.
For gut health, this can include eating a varied diet with plenty of plants and gradually increasing your fibre intake as tolerated. Prioritising sleep, staying active and managing stress can also help.
For vaginal health, avoid douching and scented soaps, and wear cotton underwear.
If you have digestive or vaginal symptoms, keep track of them and talk to your doctor, who can advise on the next steps.
Menopause resources
In this article, we’ve focused on hormones, PCOS, endometriosis, pregnancy, postpartum recovery and vaginal health. Menopause also comes with changes in the gut microbiome, which happen due to declining oestrogen levels.
You can find out more about menopause and your microbes from Dr Shahzadi Harper.
Or, read our article about menopause and gut health to learn what to expect and how to support your gut through this life stage.
Frequently asked questions
Here are answers to some common questions about women’s gut and vaginal health.
Can a gut microbiome test explain PCOS or endometriosis?
No. A gut microbiome test can only show which bacteria were present when you took the sample. There’s no validated test that can identify PCOS or endometriosis from a stool sample.
Are gut and vaginal probiotics interchangeable?
No. Your gut and vaginal microbes are very different. That’s why the types of probiotics that can support your gut microbiome are different from the ones that can support your vaginal microbiome. Check whether a specific probiotic has been tested for gut or vaginal use.
Does postpartum bloating mean my microbiome is out of balance?
Not necessarily. Bowel symptoms after childbirth can have many causes, including changing hormone levels, reduced mobility and medication. There isn’t enough research linking changes in the gut or vaginal microbiome to bloating. If your symptoms persist, speak with your doctor, health visitor or a pharmacist.
Can changing gut bacteria improve fertility?
Not based on current evidence. Some studies have found links between the gut and vaginal microbiomes and fertility, but there’s no evidence that changing your gut bacteria improves your chances of conceiving.
Sources
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Endo belly: What is it and why does it happen? – a narrative review. Journal of Clinical Medicine. (2023). Link.
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