Diversity in vaginal microbiota profiles

Vaginal microbiota is made up of five different community state types (CSTs), including three protective CSTs (respectively dominated by Lactobacillus crispatus, Lactobacillus gasseri or Lactobacillus jensenii), one disruptive CST, and one—CST III—dominated by L. iners, whose role in vaginal health remains debated. This is because the bacterium may be protective or disruptive—while it seems to be an integral part of a healthy vaginal microbiome, it is paradoxically also abundant in pathological and dysbiotic conditions and has even been implicated in colonization by Group B Streptococcus during pregnancy.

More L. iners in healthy expectant mothers

To better understand the relationship between microbial flora and vaginal health, Chinese researchers focused on the particular case of pregnant women in their third trimester—either healthy (34 women) or not (61 women with gestational diabetes, complications, infection, etc.). Their results highlight the persistence of lactobacilli predominance and the maintenance of alpha diversity across all expectant mothers.

Most notably, the type dominated by L. iners was less common in the group of sick women (31.15%) than in the group of healthy women (50%). In addition, L. iners was relatively more abundant (as a percentage of the species present) in healthy women.

Altered metabolic pathways

The increased abundance of L. iners in healthy pregnant women was associated with the overexpression of metabolic pathways favorable to a healthy pregnancy—for example, tetrahydrofolate (sidenote: Tetrahydrofolate a coenzyme derived from folic acid, primarily involved in the synthesis of nucleic acid bases (purines and pyrimidines), which constitute the DNA and RNA of genetic material. Tetrahydrofolate (THF) is also involved in the synthesis of amino acids, including methionine, histidine, and serine. ) biosynthesis, which may play various roles (microbial folate synthesis, a slightly pro-inflammatory state).

But the higher abundance of this bacterium in healthy women was also associated with glycosyltransferase (sidenote: Glycosyltransferase a membrane-associated enzyme that catalyzes the transfer of a sugar moiety onto a protein, resulting in the formation of a glycoprotein. In pathogenic bacteria, these glycoproteins have been implicated at various stages of the infection process.

Explore: Tomás JM, Fulton KM, Twine SM et al. Generation of Null Mutants to Elucidate the Role of Bacterial Glycosyltransferases in Bacterial Motility. J Vis Exp. 2022 Mar 11;(181). ) synthesis routes and antibiotic resistance, compared with women suffering from pathologies. These mechanisms may reflect the dynamic adaptation of the microbiota to the immune and hormonal environment characteristic of the third trimester of pregnancy.
 

Seven very different strains of L. iners

More in-depth analyses show that not all L. iners are alike. Among the seven strains of L. iners identified by the authors, three strains associated with bacterial vaginosis (versus four strains associated with good health) proved to be more efficient at forming biofilms, thanks to genes coding for the proteins involved. The team also showed that five of the seven identified strains (whether associated with bacterial vaginosis or not) inhibited the growth of the pathogen G. vaginalis, which is implicated in preterm birth.

These results suggest that L. iners may exert a protective influence depending on environmental conditions and the strains involved. A microbiota dominated by certain strains of L. iners could therefore contribute to the prevention of complications linked to persistent dysbiosis.

Explore the latest insights on the conditions that promote a balanced vaginal microbiota: 

For years, the scientific community has been gathering evidence that our gut and brain are in constant communication, a concept known as the gut-brain axis. ^{1, 2}  We’ve seen that the composition of the gut microbiota is different in patients with Alzheimer’s disease ³, and that this dysbiosis might contribute to the neuroinflammation that fuels the disease ^{4, 5}.

But the precise details have been blurry. We’ve been looking at the forest, but a groundbreaking new study ⁶ zooms in on the individual trees, and what it reveals could fundamentally change how we approach this Alzheimer devastating neurodegenerative disease.

Beyond the brain: not overall diversity, but specific microbial identity

What if the first whispers of Alzheimer’s disease weren’t cognitive, but compositional? A landmark study published in Alzheimer's Research & Therapy provides compelling evidence that the key to understanding, and perhaps one day diagnosing, the cognitive decline in the lives of patients affected by Alzheimer’s disease may lie within the specific species of bacteria residing in our gut.

Using high-resolution shotgun metagenomics (sidenote: Shotgun Metagenomics This is a high-resolution sequencing method that analyzes all the genetic material from every microbe in a sample. Unlike older techniques that just identify bacterial families, it allows for precise identification down to the species level and reveals the functional genes those bacteria possess. ) on patients with Mild Cognitive Impairment (MCI) (sidenote: Mild Cognitive Impairment (MCI) MCI is a clinical stage between the expected cognitive decline of normal aging and the more severe decline of dementia. Individuals with MCI have noticeable memory or thinking problems but can still perform most daily activities, representing a critical window for intervention and study. ) , a critical intermediate stage, the researchers found that there was no significant difference in the overall diversity of the gut microbiota compared to healthy controls. Instead, the crucial difference was the identity of the players. The study pinpointed 59 specific microbial species whose presence or absence was directly correlated with MCI, amyloid plaques, and tau protein (sidenote: Tau Protein Tau is a protein that normally stabilizes the internal transport system, or microtubules, within the brain's nerve cells. In Alzheimer's disease, it becomes abnormally phosphorylated and aggregates into neurofibrillary tangles inside the neurons, leading to cellular dysfunction and death. ) levels, the core pathological hallmarks of Alzheimer's disease. This tells us it’s not about the size of the microbial army, but which specific soldiers are on the front lines.

The surprising role of two Bacteroides: why species-level detail is a game-changer

Here is where the findings about gut biomarkers become truly paradigm-shifting. The study revealed that different species within the very same genus can have opposite effects on brain health. For example, the presence of the species Bacteroides eggerthii was associated with a reduced risk of MCI. Yet, another species, Bacteroides thetaiotaomicron, was linked to a higher risk.

This is a critical discovery because it demonstrates that previous studies relying on lower-resolution sequencing, which could only identify bacteria at the genus level, may have missed the most important part of the story. It’s like knowing someone is a "mammal" without knowing if it's a mouse or a lion. This species-specific activity is a fundamental insight that will force the field to adopt more precise methods.

Toward functional biomarkers: the protective role of Akkermansia

The study moves beyond mere correlation, identifying bacteria that are not just present, but are functionally tied to brain health. One of the beneficial species identified, Akkermansia muciniphila, was negatively correlated with amyloid burden. This is significant because Akkermansia is known to produce metabolites that strengthen the gut barrier and have anti-inflammatory effects. ⁷  This research suggests its role may be even more direct, potentially influencing the brain's energy metabolism and protecting against the buildup of toxic proteins, such as tau protein.

The identification of specific pro- and anti-inflammatory species tied directly to amyloid and tau levels opens the door for developing highly sensitive metabolic biomarkers, ^{8, 9, 10} potentially allowing for a diagnosis at the MCI stage, long before irreversible damage to the central nervous system occurs.

Anorexia nervosa is a psychiatric disorder classified as an eating disorder. It can have serious health consequences and carries a significant risk of becoming chronic or even fatal. Anorexia nervosa is characterized by voluntary food restriction that leads to severe weight loss and is often linked to bulimia, anxiety and behavioral disorders that can contribute to other health problems.

Psychotherapy combined with nutritional rehabilitation is the recommended approach for reestablishing normal eating habits. However, patient responses vary and some eating disorder symptoms such as bulimia and anxiety may persist.

How the microbiota impacts cognitive functions

In 2023, psychiatrists at the University of Graz in Austria identified an alteration in implicit learning (the unconscious acquisition of knowledge) that may partly explain the lack of response to treatment. In a new study, the same team suggests that this impairment could be linked… to the microbiota!²

It is known that the gut microbiota influences cognitive functions through the gut–brain axis (sidenote: Gut-brain axis Two-way communication network between the gut and the brain, which allows the gut and brain to communicate via three different pathways: 
1. the neuronal pathway (neurons), mainly via the vagus nerve and the enteric nervous system,
2. the endocrine pathway, by secreting hormones such as cortisol, adrenaline and serotonin
3. the immune system pathway, by modulating cytokines The gut-brain axis influences our behavior, cognition (memory), emotions, moods, desires, perception... and pain, among other things. ) . This axis modulates the neuroendocrine system, particularly the hypothalamic–pituitary–adrenal axis, which regulates stress responses and cortisol production. The enteric nervous system is also involved in bidirectional communication with the autonomic nervous system and the vagus nerve, as are neurotransmitters (GABA, dopamine, serotonin, etc.) produced by the microbiota.

Based on this observation, the Austrian scientists compared memory and implicit learning abilities as well as the microbiota of 15 patients with anorexia nervosa to those of 13 healthy control women.

Lower learning scores linked to less diverse microbiota

The results show that in the anorexia group:

• implicit learning scores are lower than those of healthy controls, while memory scores are similar;
• the gut microbiota shows an increased abundance of Akkermansia muciniphila, whereas in the control group, short-chain fatty acid (SCFA (sidenote: Short chain fatty acids (SCFA) Short chain fatty acids (SCFA) are a source of energy (fuel) for an individual’s cells. They interact with the immune system and are involved in communication between the intestine and the brain. Silva YP, Bernardi A, Frozza RL. The Role of Short-Chain Fatty Acids From Gut Microbiota in Gut-Brain Communication. Front Endocrinol (Lausanne). 2020;11:25. ) )-producing bacteria such as Faecalibacterium are more prevalent.

Overall, higher implicit learning scores are linked to greater microorganism diversity and a higher number of distinct species:

• a high score was associated with an increase in Actinobacteria, especially Bifidobacteria, key microorganisms in gut–brain communication that may reduce anxiety via vagal pathways and thereby influence learning processes;
• a low score, in contrast, was associated with an increase in Lachnospiraceae, which several studies have linked to depressive disorders that may impair brain function and implicit learning.

Toward new treatment approaches

Despite certain limitations (small sample size, lack of dietary and educational data, absence of male participants), this study shows promise. It opens the door to potential new treatment strategies for managing disorders such as anorexia nervosa.

Food restriction, intense fear of gaining weight, calorie obsession, body dysmorphia, bulimia, anxiety, depression, etc. Anorexia nervosa is a serious eating disorder that significantly affects a patient's health, impacting both behavior and the body. It is also particularly difficult to manage (read inset).

People affected by the condition often experience impaired cognitive function, particularly in certain learning abilities essential for behavioral adaptation, which may slow recovery.

A new study suggests the disorder could be linked to changes taking place in the gut microbiota. ⁴

A less diverse microbiota 

The authors, researchers from the University of Graz in Austria, enrolled 15 patients with anorexia nervosa and 13 healthy female controls. All participants underwent tests to assess their implicit learning ability (see inset). At the same time, their stools were analyzed to determine the composition of their gut microbiota.

The researchers’ findings confirm that patients with anorexia nervosa show lower implicit learning scores than healthy volunteers. What is more interesting, however, is that these scores are linked to microbiota composition: the higher the scores, the more diverse the microorganisms. 

When the gut microbiota scrambles the brain

How can this finding be explained? It’s well known that the gut microbiota influences brain function via the gut–brain axis. For example, it can alter stress responses or produce brain messengers (dopamine, serotonin, etc.) that can affect learning abilities.

In this study:

A high learning score was, for instance, linked to an increase in Bifidobacteria, bacteria that are key to gut–brain communication.These bacteria can help reduce anxiety and in turn influence learning processes.

Conversely, a low score was associated with an increase in Lachnospiraceae, bacteria that have been linked in several studies to depressive disorders that may impair brain function and implicit learning. These effects suggest a strong connection between the microbiota, behavior and mental health in conditions such as anorexia.

Toward a probiotic-based treatment for anorexia?

This discovery is particularly intriguing as it may help explain why psychotherapy which partly relies on implicit learning is not always effective in treating anorexia. If confirmed, it could one day be possible to use probiotics containing Bifidobacteria to improve the management of anorexia nervosa. By stabilizing the gut–brain axis, these probiotics could help women return to normal eating habits.

For years, we've known that our gut and our brain are in constant conversation. This "gut-brain axis" is why you might feel "butterflies" when you're nervous. Now, a groundbreaking new study ¹ suggests this connection is far more important than we ever imagined, revealing that the earliest clues to Alzheimer's disease may not be in the brain at all, but hidden among the trillions of bacteria living in our gut.

It’s not the size of the crowd, but who's in it

Scientists used to think that in Alzheimer's, the problem was a general loss of different types of gut bacteria, like a garden becoming less diverse. But this new research found something completely different. In people with early memory loss,(those diagnosed with mild cognitive impairment (MCI) (sidenote: Mild Cognitive Impairment (MCI) MCI is a clinical stage between the expected cognitive decline of normal aging and the more severe decline of dementia. Individuals with MCI have noticeable memory or thinking problems but can still perform most daily activities, representing a critical window for intervention and study. ) the overall number of bacterial types was fine.

The real problem was a shift in which specific bacteria were present. The study identified 59 precise types of bacteria, potential biomarkers that were either more or less common in people on the path to Alzheimer's. This tells us it's not about having fewer bacteria, but about having the wrong ones in charge.

The gut's heroes and villains can look alike

This is where the story gets truly fascinating. The study revealed that two bacteria from the exact same family can have completely opposite effects. Think of it like a family with a "good twin" and an "evil twin". One bacterium, named Bacteroides eggerthii, was linked to a lower risk of memory problems, acting like a hero for the brain. But its close relative, Bacteroides thetaiotaomicron, was linked to a higher risk, acting like a villain. This is a critical discovery because it means previous science, which couldn't tell these bacterial "relatives" apart, was missing the most important details in understanding the disease.

What are the stages of Alzheimer's disease?

Toward a new future for early detection

So, what does this all mean for you? This research is paving the way for a revolutionary new approach to diagnosis of Alzheimer’s disease. By identifying a "good guy" bacterium called Akkermansia muciniphila, which was linked to less of the toxic amyloid protein (sidenote: Toxic amyloid protein Amyloids are aggregates of proteins that fold together. In certain neurodegenerative diseases such as Alzheimer's disease, amyloid plaques form from aggregates of misfolded proteins, composed mainly of beta-amyloid protein. These plaques form around neurons and prevent them from functioning properly.

https://emedicine.medscape.com/article/335414-overview ) found in Alzheimer's patients brains, scientists are creating a "fingerprint" of a healthy gut.

One day, we might be able to use a simple stool sample to check for these specific bacterial heroes and villains. This could help spot a person's risk for Alzheimer's years earlier than we can now, opening a crucial window to protect brain health through diet and lifestyle.

Colorectal cancer (CRC) is the third most common type of tumor and also the second deadliest cancer. The gut microbiome appears to play a crucial role in carcinogenesis. However, research is still too limited to use microbiota as a clinical screening tool, even though early detection would increase the chances for survival. 

This is why studies published in 2025 in Nature Medicine are so important. They are based on the analysis of 18 datasets: 12 from pre-existing databases including 2,116 individuals (930 patients with CRC, 210 with adenomas and 976 healthy controls) and 6 from new cohorts (1,625 individuals) providing information on both the cancer’s stage and the tumor’s location in the body. In total, the study included 3,741 individuals, providing strong statistical power and potentially accurate results

Species involved, including oral bacteria

The authors detected 3,866 bacterial species, 15 eukaryotes and 23 archaea. The microbiota of healthy controls differ markedly from that of CRC patients, confirming results from previous studies: 125 species are more abundant in patients (106 known and 19 unknown) and 83 in controls (53 known and 30 unknown).

Five subspecies of F. nucleatum were among those more abundant in patients, namely, F. nucleatum subsp. animalis, vincentii (two different subspecies), nucleatum, polymorphum. Other bacteria previously associated with CRC, such as P. micra and B. fragilis, were also identified.

The gut microbiota may be involved in regulating ammonia in the CRC tumor micro-environment.

A significant portion of CRC-specific gut bacteria are typically oral species, with 21 of the 125 species more abundant in patients (16.8%) being oral in origin, including 11 commonly found in dental plaque.

Predicting colorectal cancer

Above all, this large dataset has improved the accuracy of colorectal cancer (CRC) prediction based on a simple stool sample: the area under the curve (AUC), a measure of model performance, now reaches 0.85 —an improvement over previous studies, which achieved a maximum of 0.81. A large part of this predictive power relies on bacteria that are typically oral in origin.

The authors also show that:

• microbial biomarkers are linked to the presence of a tumor,
• they vary according to disease stage: the abundance of P. micra and F. nucleatum increases as early as stage I CRC, while Akkermansia muciniphila and Parabacteroides distasonis rise in advanced stages, suggesting that microbiota changes occur continuously and intensify as cancer progresses (adenoma–carcinoma sequence).
• they also differ depending on tumor’s location: for example, three oral species were significantly more abundant in proximal colorectal cancer.

Previous studies had implicated ammonia in the tumor micro-environment in T-cell depletion and cancer progression.

Rather than “feel good in your skin”, should we be saying “feel good in your skin microbiota ”?

So suggests a British study, linking psychological well-being to the microorganisms living on our skin, specifically the skin of the face, scalp, forearms, and armpits, based on a study of 53 Britons with an average age of 63. This research highlights a system of interactions between the skin and the brain, echoing the now familiar dynamics of the gut-brain axis.

More Cutibacterium, more well-being?

The study shows for the first time an increased abundance of certain bacterial genera in those who feel the best in their skin, both in terms of general well-being and the well-being of the skin area in question. The skin bacterium most common to Britons who feel the most comfortable in their bodies is Cutibacterium (sidenote: Cutibacterium A bacterial genus whose classification has been significantly revised in recent years (until 2016, it was known as Propionibacterium). The genus includes several species, including the infamous C. acnes (an opportunistic pathogen involved in acne and infections of breast implants, shoulders, etc.), as well as C. avidum, C. granulosum, C. namnetense, and C. humerusii Ahle CM, Feidenhansl C, Brüggemann H. Cutibacterium acnes. Trends Microbiol. 2023 Apr;31(4):419-420. ; CTCB ) . Do you have plenty of it on your face? Then you must be fairly stress-free. If your armpits are teeming with it, your mood is likely to be good and your stress levels low. Conversely, a lower abundance of Cutibacterium may contribute to disorders such as stress, anxiety, or depression.

This is somewhat surprising, since Cutibacterium is usually associated with C. acnes and the puberty nightmares that come with it, rather than elderly Britons enjoying their golden years. This bacterium could also promote positive skin health by inhibiting pathogens and regulating skin acidity, thanks to its ability to convert sebum into free fatty acids.

Cause or effect?

The central question is, as always, whether the presence of Cutibacterium is a cause or effect of well-being. In other words, does the presence of Cutibacterium make us happy, or does a cheerful disposition attract Cutibacterium to the skin? Or could it be a third factor common to both, such as lifestyle, exercise, or diet?

At present, we can’t say. We do know that the skin and its microbiota act as a protective barrier for the body, inhibiting pathogens, and thus providing security and peace of mind. Conversely, it has been shown that stress, anxiety, and depression can impact our skin, leading to skin disorders such as eczema (or atopic dermatitis), psoriasis, acne, and underarm odor.

We’ve heard of the gut-brain axis, and now we know there’s a bidirectional skin-brain axis as well, with the former influencing the latter and vice versa. For the first time, a link has been found between skin microbiota and psychological well-being. This should encourage psychodermatology (sidenote: Psychodermatology Psychodermatology is a relatively new field of medicine. It encompasses the interaction of mind and skin. Treatment of psychodermatological disorders focuses on improving function, reducing physical distress, diagnosing and treating depression and anxiety associated with skin disease, managing social isolation and improving patient’s self-esteem. Both pharmacological and psychological interventions are used in treating psychodermatological disorders. Explore Jafferany M, Franca K. Psychodermatology: Basics Concepts. Acta Derm Venereol. … ) research to further study the bacteria involved and their potential influence on our skin and general health.

What do we already know about this subject?

The vaginal microbiota plays a key role in defending against pathogens, maintaining mucosal immunity, and supporting reproductive health. Dominance by Lactobacillus species, especially L. crispatus, maintains a low pH and inhibits pathogenic colonisation² . Dysbiosis — defined by a loss of lactobacilli and overgrowth of anaerobic species such as Gardnerella or Prevotella — is associated with increased risks of bacterial vaginosis (BV), preterm birth³ , infertility⁴, sexually transmitted infections, human papillomavirus (HPV) infections and gynaecological cancers⁵ . Previous studies have shown that hormonal changes, menstruation, and sexual intercourse can influence the composition of the vaginal microbiome⁶. Many of these studies relied on infrequent sampling and lacked resolution to assess short-term fluctuations or determine the drivers of transitions between eubiosis and dysbiosis. The contributions of viral dynamics and functional bacterial genes have remained largely unexplored.

What are the main insights from the study?

This study introduces the concept of VCDs, offering a new framework for classifying microbiome behaviour across the menstrual cycle. Unlike community state types (CSTs), which describe static microbiome compositions, VCDs capture temporal patterns that may better reflect microbiome resilience and vulnerability. The four VCDs — constant eubiotic, constant dysbiotic, menses-related dysbiosis, and unstable dysbiotic — represent distinct profiles of microbial stability. Women in the constant eubiotic group maintained Lactobacillus dominance throughout the cycle, while those with constant dysbiosis had persistent BV-associated communities. Menses-related dysbiosis was characterised by temporary shifts during menstruation, often reverting mid-cycle, whereas the unstable group experienced abrupt fluctuations after exposures like sexual intercourse, suggesting greater ecological fragility.

One of the key findings was that instability in the vaginal microbiome is associated with increased bacteriophage activity and a higher prevalence of L. iners. This species is frequently linked to transitional or less stable states, and phage abundance may reflect active lytic cycles that destabilise dominant bacteria via “kill-the-winner” dynamics. Additionally, women with transient dysbiosis showed increased abundance of potential pathogens such as Sneathia spp. during and after menstruation, pointing to specific periods of vulnerability.

Strain-level analysis revealed differences in bacterial gene content, including bacteriocins produced by Gardnerella leopoldii that may inhibit lactobacilli. These genes were more prevalent in unstable and dysbiotic VCDs, supporting a possible mechanistic role in shaping community structure. Although these genetic findings require further validation, they highlight the importance of moving beyond species-level classification to understand microbial function and its impact on host health.

What are the consequences for clinical practice?

This study underscores the need to rethink how vaginal health is assessed and monitored in clinical practice. The recognition that vaginal microbiota are dynamic — and that stability patterns differ markedly between women — has implications for diagnostics, risk assessment, and therapeutic strategies. Sampling at a single time point, especially during menstruation, may fail to capture meaningful fluctuations or misrepresent a woman’s baseline microbial state. Clinicians should consider collecting samples at multiple points in the cycle to better assess microbiome behavior, particularly in patients with recurrent symptoms or reproductive concerns.

The limitations of CST-based classification are evident in this study. Two women with the same CST may exhibit entirely different VCDs, one with stable eubiosis and the other with frequent dysbiosis. Incorporating VCD assessment could enable more personalised interventions, such as recommending prophylactic microbiome support for women with unstable patterns or targeting high-risk windows (e.g. post-menses) for infection screening.

The identification of phage-driven instability and strain-level bacterial traits opens avenues for precision medicine. Future therapies may need to address microbial function — such as biofilm formation or bacteriocin production — rather than composition alone. Understanding the dynamics of vaginal bacteriophages could also inform novel microbiome stabilisation strategies.

Figure 1. Vaginal time series can be classified into four categories (Vaginal Community Dynamics) according to their proportions of eubiotic samples

a. A decision tree can separate a time series of samples into dynamic groups, based on the community state types (CSTs). Input from the user determines which CSTs are considered eubiotic (here: I, II, and V) and which days are to be considered free from the influence of menses (here: cycle day 9 to cycle day 25). Time series with ≥80% eubiotic samples are considered constant eubiotic; conversely, those with >80% dysbiotic samples are considered constant dysbiotic. For those in the 20–80% range, a second assessment is done on the days free of menses: if they are >80% eubiotic, the time series is considered menses-related dysbiotic, and otherwise unstable (changing from eubiosis to dysbiosis without a clear temporal pattern). b. A colour map with one individual per row and one day per column. The colour of each intersection depicts CST. Coloured bars on the left side show the vaginal community dynamics of each woman. c. Additional colour bars show the inferred vaginal community dynamics of each participant when using fewer samples for classification. Reproduced from Hugerth LW, et al. Microbiome 2024, 12, 1531 (doi:10.1186/s40168- 024-01870-5) under a CC-BY 4.0 license (creativecommons.org/licenses/by/4.0). No changes have been made to the figure.

The classification tool VALODY, designed to assign VCD categories based on VALENCIA CST assignments, is available on GitHub at https://github.com/ctmrbio/valody.

How the menopausal microbiome impacts women’s overall health

Menopause-induced changes lower gut microbiome diversity and cause a shift toward greater similarity to the male gut microbiome. This review details the healthrelated consequences of these changes. During perimenopause, a gradual decline in hormone levels disrupts the gut microbiome balance and contributes to adverse health outcomes, including cardiometabolic disease and changes in oestrogen metabolism. Hormonal fluctuations during menopause change the oral microbiome, heightening the risk for dental caries, periodontitis, and oral infections such as candidiasis. Menopauseinduced vaginal microbiota alterations increase susceptibility to bacterial vaginosis, vulvovaginal atrophy, and recurrent urinary tract infections. Menopause also alters the diversity and abundance of gut microbiota that have been linked to inflammation. Chronic dysbiosis-induced inflammation predisposes menopausal women to metabolic disorders and autoimmune diseases.

This article bridges the gap between endocrinology and microbiology, and emphasises the systemic impact of menopause beyond reproductive health. A key strength of the review is its holistic examination of menopausal-related hormonal fluctuations with corresponding shifts in gut and vaginal microbial composition and diversity. This opens the door to exploring microbiome-based biomarkers for managing menopausal symptoms such as genitourinary syndrome, metabolic changes, or inflammation. This article’s interpretation of age-related changes in women’s health enriches the growing interest in the human microbiome’s role in disease. While hormone replacement therapy has shown promise in mitigating some of the adverse effects of oestrogen deficiency, its broader application is limited by its systemic risks. The targeted use of specific probiotics to restore gut microbial balance, coupled with dietary and lifestyle modifications, may offer safer, more individualised alternatives that mitigate adverse health effects of menopause.

Menopausal microbiome research is overrepresented with data from Western populations and a lack of detailed mechanistic insights. Since diet, lifestyle, and environmental factors significantly influence the microbiome, we need ethnically and geographically diverse research incorporating advanced “omics” approaches to fully elucidate these influences. More effective, personalised treatment strategies will then emerge that can improve the quality of life for menopausal women.

In conclusion, menopause is a whole-body transition involving significant changes in the microbial ecosystem. Understanding and addressing these changes can enhance patient outcomes and promote healthier ageing in women.