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adversities has been linked to altered GM profiles in children, with specific microbial taxa associated with
adversity exposure. These alterations are reflected in the child’s socioemotional functioning, supporting the
idea that intergenerational transmission of adversity may affect mental health through changes in GM
[177]
function . Moreover, variations in the GM, along with inflammatory markers, may represent mechanistic
pathways for the observed health outcomes. For instance, GM characteristics could predict social
disadvantage and psychosocial stress, highlighting microbial imbalances as mediators of early adversity
effects . This evidence suggests that ELS can induce microbial changes predisposing individuals to
[178]
conditions like asthma and diabetes.

ELS has also been linked to later-life health issues, including inflammatory diseases and cardio-metabolic
disorders [121,181] . In addition, ELS-induced GM dysbiosis plays a particularly crucial role in depression
through gut-brain axis communication [142,183] . Inadequate or insufficient microbial exposure in early life can
lead to inflammatory responses associated with several conditions, such as allergies, obesity, T1D, and
generalizability and comparability of results. Further research employing consistent stressors, validated
cardiovascular diseases [121,184-186] . Furthermore, childhood trauma has been shown to negatively impact stress
recovery, with heart rate indices indicating impaired recovery, further emphasizing the long-term effects of
ELS on health. These findings point to enduring impacts on both physical and psychological well-being in
adulthood . Thus, understanding the mechanisms behind early-life GM dysbiosis is essential for
[179]
identifying potential interventions to mitigate the risk of chronic diseases.

Maternal stress is another key factor influencing both maternal and infant microbiota. Prenatal and
postnatal stress can lead to volatile shifts in infant GM that are specific to certain developmental stages ,
[180]
indicating a complex relationship between stress and microbiome development, as well as potentially
exacerbating the risk of chronic diseases in offspring. Early exposure to maternal stress may predispose
individuals to conditions like obesity, cardiovascular diseases, and neurodevelopmental disorders, with a
disrupted GM playing a central role . Furthermore, stress-related changes in the microbiome may involve
[181]
[182]
epigenetic modifications that adapt the gut-brain axis to stress .
Although several studies have reported a connection between ELS and the GM during prenatal and
postnatal periods, a unified microbiome signature linked to either prenatal or postnatal stress has not yet
been completely established [177,178,180] . This variability in findings is likely attributable to a range of
methodological differences, including variations in experimental designs, age groups, geographical
locations, ethnic backgrounds, assessment tools, timing of sample collection, analysis techniques, sample
sizes, and the nature of stressors examined. In addition, differences in microbial composition across regions
or populations, as well as the source of the samples (e.g., human vs. animal models, or hospital vs.
community-based samples), can contribute to observed inconsistencies. These factors may impact the

stress metrics, and high-resolution microbiome analyses is essential to establish clear connections between
stress and the human GM [187,188] .

Mulder et al. found that specific domains of ELS, such as socioeconomic stress, presented limited evidence
of association with the GM, suggesting that other factors may also be implicated . However, the limited
[158]
number of longitudinal studies and controlled intervention trials on this topic makes it difficult to establish
a clear causal relationship. Consequently, future research is necessary to establish causality and determine
whether various modifiable factors might be effectively targeted to improve gut health, particularly in
children facing heightened contextual stress or adverse conditions. Understanding the mechanisms by
which these factors influence the GM is crucial, as it could facilitate the development of customized
interventions that mitigate the adverse effects of ELS.