The Link Between Bacteria and Brain Development
These days it’s difficult to avoid the topic of microbes and their relationship to your health. The thriving universe of bacteria that lives on and inside your body (your microbiome) includes good actors as well as pathogens. Both are constantly flexing their muscles, influencing bodily functions like metabolism and mood. For instance, gut bacteria pull the strings on emotional health by producing chemical messengers like serotonin that help to keep you mellow. Now we’re seeing that microbes can also impact how your brain develops, even before you are born.
Stress is the Link
The connective tissue embodies maternal stress. And here’s where the microbiome comes into play. One of the body’s core stress regulators is the hypothalamic-pituitary-adrenal (HPA) axis. Not only does stress precipitate long-term changes to the HPA axis, it also reduces the ratio of beneficial gut bacteria. When these disruptions occur during pregnancy, they can impact how the offspring’s brain develops, both in utero and after birth.
A swath of studies connects maternal stress during pregnancy with poor birth outcomes, some of which affect cognitive development. These include developmental delays and increased cortisol levels. Gut microbes have usually not come into play other than with autism spectrum disorder, which has been uniquely associated with bacterial imbalance for years.
Stress Upsets Microbes
Laboratory studies have shown that stress during the first week of pregnancy disrupts the mother’s microbial ecosystem. Pathogenic bacteria proliferate at the expense of beneficial types. Although scientists don’t fully understand the mechanisms, when bad guys have the edge, it disrupts pathways along the HPA that impact fetal brain development.
The Effects Are Long-Lasting
Microbial imbalances initiated in pregnancy also determine the mother’s vaginal microbiome and, therefore, the microbes that are transferred to her infant at birth. Stress during pregnancy decreases the ratio of beneficial bacteria seeding the baby’s microbiome, as does a C-section delivery. A mother’s breast milk is also impacted by the quality of her microbiome. All these processes overlap, potentially chipping away to modify how the newborn’s brain develops.
The good news is that mothers who transmit higher ratios of beneficial bacteria may be building better brains in their offspring. A recent study of more than 400 infants found that boys with a higher proportion of the “good guy” phyla Bacteroidetes, were programmed for better cognition and language skills. (As a group, girls have more Bacteroidetes and are inclined to cognitively outperform boys at this stage.) The suspected link is sphingolipids, a substance produced by the bacteria, which supports healthy brain development.
Another study of 40 families connected the microbial profiles of children aged 5 to 7 with their socioeconomic status and behavioral problems. Children with more status and stable family dynamics had higher levels of a specific bacteria (Bacteroides fragilis) and were less likely to behave aggressively. Researchers have linked intestinal inflammation with mood disorders and they suspect that the anti-inflammatory properties of the bacteria played a role in these results.
That study did not investigate the impact of diet, a key factor in both microbiome health and inflammation. Eating a nutritious diet of whole foods, built around a wide variety of plant foods like vegetables, fruits, whole grains and legumes is the best way to build a robust microbiome. Fermented foods and omega-3 fatty acids (which have been specifically linked with healthy neurodevelopment) also encourage bacterial diversity. Certain bacteria produce substances that fight inflammation, among other benefits.
A Nutritious Diet Makes Sense
Emerging research suggests that a healthy diet can protect a pregnant woman’s microbiome and her developing baby from the disruptive spiral sparked by stress. The microbiome plays a regulatory role in pregnancy and it makes sense to keep it in tip-top shape.
For instance, gut bacteria mediate how well a pregnant woman’s body utilizes the nutrients she consumes. Some nutrients, including iron, certain B vitamins and vitamin D, are vital for a healthy pregnancy. Moreover, “good guy” bacteria manufacture certain nutrients, including folate, long identified as a key player in healthy brain development.
While we are far from having all the answers, it’s become increasingly clear that a robust microbiome works in partnership with the mother ‘s body to support healthy pregnancies that include sound neural development. Future research will shed more light on the pathways involved. In the meantime, strategies that nourish the microbiome, including a healthy diet and adequate exercise will help to ensure the best pregnancy outcomes, paving the way toward a smarter child.
Judith Finlayson is the author of You Are What Your Grandparents Ate: What You Need to Know About Nutrition, Experience, Epigenetics, and the Origins of Chronic Disease. Visit her at www.judithfinlayson.com.
Jašarević, E. et al. Stress during pregnancy alters temporal and spatial dynamics of the maternal and offspring microbiome in a sex-specific manner. Scientific Reports 2017.
Tamana, S. et al. Bacteroides-dominant gut microbiome of late infancy is associated with enhanced neurodevelopment. Gut Microbes 2021
Flannery, J. et al. Gut Feelings Begin in Childhood: the Gut Metagenome Correlates with early environment, Caregiving and Behavior. mBio 2020
Jahnke, J. et al. Maternal precarity and HPA axis functioning shape infant gut microbiota and HPA axis development in humans. PLOS ONE 2021