A recent research paper from the University of Helsinki, “Effects of maternal microbiota and microbial metabolites on the fetal gut, brain and placenta,” caught my eye.
The microbiome is a unique community of approximately 100 trillion bacterial cells, fungi, and viruses that live in the gut. Everyone's microbiome is different and is controlled not only by what we eat and drink, but also by many other factors, including sleep, exercise, social relationships, and environment.
Until recently, biologists would have disparagingly referred to bacteria as “bags of enzymes,” but nowadays gut microbes are the real deal, and scientists are eagerly studying their impact on human health and disease.
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For example, the Finnish study mentioned above compared fetuses from mothers living in a normal environment to fetuses from mothers living in a germ-free, sterile environment, and found that fetuses from mothers living in a normal environment had enhanced immune systems and host-microbe interactions.
Similarly, genes related to nervous system development and function in the fetal brains of mothers in normal environments (researchers usually say “related” because there are so many unknown factors in biological and psychological experiments, and rarely “cause” them) and genes in the placenta that control pregnancy were significantly more active than in the control group.
Male mice were more affected than female mice, and there is much speculation as to why males had a higher overall morbidity and mortality rate than females. We will address that question in a future post.
“Our study helps us understand the causes of these diseases and has the potential to improve their prevention and treatment in the future,” said Michael Nik, lead author of the study.
A Swedish (still Nordic) study followed 16,440 children for 20 years. Of this cohort, 1,197 developed neurodevelopmental disorders. Researchers found that children of mothers with disrupted gut microbiomes had a number of biological markers associated with earlier onset of mood disorders and gastrointestinal disorders, along with an increased risk of developing autism spectrum disorders, ADHD, communication disorders, language disorders, and intellectual disabilities in the future.
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This was especially true for mothers who gave birth prematurely and those who were stressed, smoked, had an infection, or were taking antibiotics.Not surprisingly, breastfeeding gave these children a healthier gut flora, conferring a protective effect against the diseases mentioned above.
“What's remarkable about this study is that these biomarkers were found in umbilical cord blood at birth or in the stool of children as young as one year, more than a decade before diagnosis,” said Eric W. Triplett of the University of Florida.
While there has been a lot of research on the intergenerational transmission of trauma over the past few decades, only a few studies, led by Bridget Callahan of UCLA, have looked at the impact of adversity on women and their microbiomes. In some cases, the adversity occurred before the child was even conceived. The researchers collected data on the lives of 450 mother-child pairs living in Singapore. The children of these mothers were divided into three distinct groups in terms of their gut bacteria and experiences.
“Children whose mothers suffered from anxiety disorders during pregnancy had one type of microbiota, while children whose mothers were abused or neglected all had another type of microbiota. Children who had experienced stressful events also had a different microbiota composition. This study further supports a long-established maxim in genetics that stress reduces gut microbiota diversity, which negatively impacts human mental and physical health.”
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It is widely known that there is a continuous two-way communication between the gut and the brain, called the gut-microbiota-brain axis. Disturbances in the balance and function of the gut microbiota, called dysbiosis, can disrupt these pathways and lead to changes in the permeability of the blood-brain barrier, resulting in a variety of pathological dysfunctions, including neurological disorders, psychological disorders, and gastrointestinal disorders.
The vagus nerve is the main highway connecting the brain, heart, and gut, with signals constantly traveling in both directions. In addition to the vagus nerve, complex interactions between the gut microbiome and the brain also occur through other neural, immune, and metabolic pathways.
Must-Read Articles on the Microbiome
Furthermore, it has been shown that psychological stress can alter the composition of the gut microbiota, and as a result, microbiota dysbiosis can affect emotional behavior.Dysbiosis of the gut microbiota is increasingly recognized as a contributing factor in the development of many psychiatric disorders, one of which is major depressive disorder (MDD), which is generally considered a leading cause of disability worldwide and is more often associated with death and suicide than other psychiatric or medical disorders.
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Studies in germ-free rodents have explored the potential causal role of microbiota dysbiosis in depression: after transfer of fecal microbiota from MDD patients to antibiotic-treated rats, these rats develop depression-like behavioral and physiological symptoms: gut microbiota diversity is reduced, serotonin levels are reduced, and neurotoxic metabolites in the blood are increased.
Studies in which fecal microbiota from MDD patients was transferred to antibiotic-treated rats, who then developed depression-like behavioral and physiological symptoms, have demonstrated that the microbiota plays a pivotal role in health and disease.
Commensal microbes can alter behavior and influence the development and severity of neurological diseases, (11) regulate nutrition and metabolism, and have been shown to be important for immune system development and function.
Our gut bacteria deserve more respect. They're not the enemy. If we treat them right and feed them a varied diet, they work hard to keep us in tip-top shape.
References
Husso, A., Pessa-Morikawa, T., Lahti, L., … & Niku, M. (2023). Impact of maternal microbiota and microbial metabolites on the fetal gut, brain, and placenta. BMC biology, 21(1), 207.
Ahrens, AP, Hyötyläinen, T., Petrone, JR, Igelström, K., George, CD, Triplett, Eric W, Garrett, TJ, … & Ludvigsson, J. (2024). Infant microbiome and metabolites suggest childhood neurodevelopmental disorders. Cell, 187(8), 1853-1873.
Lev-Wiesel, R. (2007). Intergenerational transmission of trauma across three generations: An exploratory study. Qualitative Social Work: Research and Practice, 6(1), 75-94.
Sasso, JM, Ammar, RM, Tenchov, R., Lemmel, S., Kelber, O., Grieswelle, M., & Zhou, QA (2023). Gut microbiome-brain connections: A global perspective on mental and gut health and disorders. ACS Chemical Neuroscience, 14(10), 1717-1763
Zhang, YJ, Li, S., Gan, RY, Zhou, T., Xu, DP, & Li, HB (2015). Impact of gut bacteria on human health and disease. International Journal of Molecular Science, 16(4), 7493-7519.
