Factors Influencing the Vaginal
Microbiome
Other exogenous factors influence vaginal health and should be examined
as they may play a significant role in influencing reproductive health
outcomes and themselves may be associated with microbiome composition.
In the United States, differences in health outcomes for groups defined
by race/ethnicity are oftentimes confounded by inter-group differences
in socioeconomic status, social determinants of health, and health
behaviors linked to social determinants of health. The following
sections will explore how vaginal hygiene practices, diet, sexual
partners and practices, gender affirming treatments, stress, and social
determinants impact the vaginal microbiome.
Douching and Hygiene
Practices
The vagina is colloquially referred to as a “self-cleaning oven”
because of its ability to maintain its cleanliness and health
independent of the use of soaps or human-made cleansers. Despite this,
the feminine hygiene market is a $1.1 billion dollar industry as of
2018 and is expected to continue to
grow37.
Vaginal hygiene products include washes, wipes, moisturizers and creams,
and other products. Researchers must be careful to use language that
includes the diverse range of products people could be using, as asking
about douching practices alone will not capture the full range of
vaginal hygiene products known to impact the vaginal microbiome.
The use of vaginal cleansing products can have detrimental effects on
vaginal health through several mechanisms. Soap is basic; the use of
intravaginal vaginal cleansing products can disrupt the microbial
community and prompt changes in the composition of the vaginal
environment that can contribute to the development of disease38,39.
Additionally, douching is capable of inhibiting the growth of
Lactobacillus in
vitro39and changing the vaginal microbiome of women undergoing STI treatment40.
One study found that of 1435 participants in Canada, 95% reporting
using at least one vaginal hygiene product. Participants who used any
vaginal product had nearly three times higher odds of an adverse health
condition such as reported history of BV, yeast infection, UTI, or
STI41.
Diet
The human diet independent of probiotic consumption appears to impact
the vaginal community. A study comparing the vaginal microbiomes of
seven different primate species recently found that Lactobacillus
dominated vaginal communities are a uniquely human
phenomenon10.
This is driven by the increased starch in human diets, which leads to
increased glycogen deposition in the vaginal wall. As Lactobacillus
breaks down glycogen for nutrients, the human vaginal environment became
an excellent host for Lactobacilli species. It remains unclear if
ɑ-amylase is always required for Lactobacillus to break down
glycogen10,42,
and what level of starch consumption must be maintained for
Lactobacillus to be viable in the vagina.
Studies examined the impact of probiotics in the form of yogurt and
capsulated freeze dried bacteria on vaginal symptoms. More thorough
reviews are provided elsewhere43–45,
though an overview is provided here. While oral probiotic administration
has been found to have a beneficial effect on vaginal symptoms and some
pregnancy outcomes46–48,
a vaginally administered probiotic was found to have no clinical effect49.
A clinical trial investigating the effects of probiotics on preterm
birth found that, while the probiotic did not reduce incidence of
preterm birth, it did shift the composition of the vaginal microbiome
towards an environment that is associated with lower inflammation and
pathogen abundance50.
A prospective cohort study found that women who ate milk-based
probiotics containing Lactobacillus had lower rates of preterm
birth and preeclampsia51.
Despite these findings, a recent meta analysis did not find an effect of
probiotics on preterm birth48.
Further research needs to determine the mechanisms at play and whether
probiotics are truly beneficial for vaginal health.
There is also evidence that micronutrients impact the vaginal microbiome
and vaginal health. Increased dietary fat is associated with increased
risk for BV, while increased intake of folate, vitamin A, and calcium
was associated with decreased risk for BV52.
A study of the fecal microbiome of lactating women found that
micronutrient intake was associated with the relative abundance of
specific, individual taxa53.
Only the relative abundance of the phylum Firmicutes increased as more
nutrient rich food was consumed. This implies that any dietary
interventions will need to tailor the intervention to the specific
health condition or taxa that is targeted. Taken together, these
findings may be especially important for understanding the dynamics of
the vaginal microbiome for patients who don’t have access to or don’t
consume nutrient rich food.
Sexual Partners and
Practices
Sexual partners impact the vaginal microbiome as there is direct contact
between genitals and transfer of microbiota and fluids. Individuals with
more sexual partners are consistently found to have a more diverse
vaginal microbiome17,18.
This is thought to be due to exposure to many microbes, as each sexual
partner can carry different microbes and the disturbance of the vaginal
microbiome as a result of fluid exchange between partners (whether that
be saliva, semen, or vaginal fluid). Having more female sexual partners
is associated with higher risk for exposure to pathogenic microbes, as
female partners are more likely to carry BVAB, Group B Streptococcus,
and other microbes thought to be detrimental to vaginal
health54.
It is thought that increased vaginal microbiome diversity, whether from
the number or sex of sexual partners, is overall negative for vaginal
health. However, this primarily rises out of the concept that diversity
is present in unhealthy vaginal communities when Lactobacillus is in low
abundance or absent. It is unclear whether diversity alone is a risk
factor for poor vaginal health.
Sexual practices also have been shown to impact the vaginal microbiome.
Increased male condom use is found to be associated with decreased risk
for BV, likely due to exposure prevention11,28,55.
Similarly, male circumcision is associated with decreased risk of BV for
female sexual partners. Unprotected receptive oral sex appears to be
associated with increased risk for BV, though this finding is not always
replicated56.
The effects of lubricant on the vaginal microbiome remains significantly
understudied, but a recent observational study found that lubricant use
in the day prior to vaginal sampling was associated with a higher Nuget
score57.
Birth control method and vaginal sex after anal sex are also associated
with changes in the microbiome3,55,
those these changes are not clearly defined yet.
Gender Affirming
Treatment
It is important for health care providers to be prepared to care for a
diverse population of patients, and for health science researchers to
contextualize their research to the care provided for different
populations. This includes groups utilizing hormone therapies and other
gender affirming treatments. Gender affirming treatments, such as
masculinizing hormone therapy or neovaginal surgery, can impact the
vaginal microbiome in clinically important ways. Masculinizing hormone
therapy was found to increase the diversity of the vaginal microbiome,
and individuals undergoing this treatment were more likely to fall into
the Diverse
CST58.
Longitudinal sampling will be required to identify whether masculinizing
hormone therapy changes one’s CST or if the baseline CST is the diverse
group.
One gender affirming therapy for transgender women is neovaginal
surgery, in which a vagina is constructed from existing penile and
scrotal tissue and/or a colon graft. While research on the vaginal
microbiome of those who undergo neovaginal surgery has been limited, new
research indicates that understanding the neovaginal microbiome is
clinically important. One study found that the neovaginal microbiome was
highly diverse, composed largely of anaerobic bacteria, and triggered a
host response similar to the response to BV59.
Another study examining the neovaginal microbiome of five women with
candida infection following neovaginal surgery found these women also
had more BVAB in their vaginal microbiome60.
Importantly, all five women in this study experienced several negative
vaginal symptoms that were attributed to the microbiome and not just
candida infection. In both studies, it was found that their vaginal
microbiome was more similar to the skin and gut microbiome, possibly due
to skin grafts during neovaginal surgery. There is high therapeutic
potential in understanding how the vaginal microbiome contributes to
symptoms following neovaginal surgery, but it is a multifaceted problem
with many important considerations reviewed extensively in Mundluru &
Larson,
201861.
Stress
Stress can capture many different experiences, from physical stress to
psychosocial stress. Several mechanisms of stress-induced vaginal
community disruption have been identified. First, stress-induced
cortisol can bind to glucocorticoid receptors in the vaginal wall, which
leads to an increase in proinflammatory cytokines, chemokines, and cause
immunosuppression62.
Further, stress-induced cortisol can inhibit the deposition of glycogen
in the vaginal lining in a manner which restricts the Lactobacilli
population63.
It is possible that people who experience higher levels of stress have a
vaginal microbiome that has adapted to rely on anaerobes which create an
acidic environment without solely relying on Lactobacillus. Healthy
Black and Hispanic individuals, who are less likely to harbor
Lactobacillus in their vaginal microbiome, are more likely to experience
high levels of stress and more likely than those of other ethnicities to
have anaerobes in their vaginal community 5,69. Taken
together, this indicates that the vaginal microbiome adapts to not rely
on Lactobacillus in the face of stress, as stress makes the vaginal
environment less hospitable to Lactobacillus.
Broader Social
Determinants
Social determinants of health refer to the social and economic context
in which someone is born and lives that influence their
health64.
This can manifest as access to affordable healthcare and housing,
experiences of discrimination, and structural
oppression65.
Groups who experience greater disease burden tend to be impacted by
social determinants of health. While there has not been research that
has specifically examined how social determinants impact the vaginal
microbiome, there has been work that indicates access to care and other
social determinants impact the microbiome in a clinically relevant
way66.
A further review of the microbiome through the lens of social equity is
available67and is important for thinking about how structural barriers impact the
health of one’s microbiome. It is plausible that physiologic adaptations
and changes in the microbiome may be driven by larger societal and
systemic stressors such as racism, poverty, and education which
influence health behaviors, decisions, and choices.