Although many studies have shown that, in rodents, prenatal stress affects gut microbiomes way into adulthood, how long after birth such effects last in humans is less understood.
Now, a team of researchers led by the University of California, Los Angeles (UCLA) has found that hardship experienced by mothers during their own childhood or pregnancy is reflected in the composition of their two-year-old children’s gut microbiome, which likely affects the latter’s socioemotional development. This study is the first to document the transgenerational effects of adversity on the human gut microbiome.
A growing body of research has shown that the gut microbiome affects brain and immune functioning and that changes in the community of microorganisms are connected to how hardship impacts children’s socioemotional development.
Previous studies on rodents have found that prenatal stress disrupts maternal vaginal and gut microbiomes. Thus, since babies acquire their first gut microbes passing through their mothers’ birth canals, the mother’s microbiome is likely to have a major influence on that of the offspring.
Studies conducted on humans have found evidence that, shortly after birth, stress experienced by the infant in the womb – as well as the mother’s own psychological distress – influence the infant microbiome.
Although the effects of prenatal stress on rodent microbiomes are known to persist into adulthood, until now scientists were not aware of how long after birth such disturbances remain in humans, or whether they could affect subsequent generations.
To answer this question, the researchers enrolled a cohort of 450 mother-child pairs in Singapore – when the children were two years of age – and investigated the consequences of maltreatment to mothers during their childhoods, anxiety while pregnant, and their children’s exposure to stressful life events.
Mothers were asked to recall abuse, neglect, or other maltreatment they experienced during their own childhoods and were screened for anxiety during the second trimester of their pregnancy.
In addition, the experts interviewed the children’s primary caregivers to assess what stressful events the children had experienced during their first two years of life, and tested their stool samples to map the composition of their microbiomes.
Finally, the scientists controlled for variables such as family income, which is known to serve as a proxy for childhood adversity.
The analyses revealed that children whose mothers reported more anxiety during pregnancy had microbiomes in which various species of microorganisms had populations of similar sizes – a metric biologists call “evenness” – which is different from the typically “lumpier” aspect of the microbiome, with some species being more abundant than others.
Moreover, children who experienced stressful life events after birth also exhibited less microbial genetic diversity, meaning that the microorganisms living in their guts were more closely related to each other than they usually are.
Although more experiences of adversity were found to be correlated with less microbial genetic diversity in each child, the amount of adversity did not appear to affect the similarity between different children’s microbiomes, which were still significantly different from one another.
“There are lot of questions around whether more diversity or evenness is better or worse when the gut microbiome is developing during childhood, so we don’t know if more is better at two years old,” said lead author Francesca Querdasi, a doctoral student in Environmental Biology at UCLA.
“But many of the species we found to be related to adversity are known to interact with the immune system in some way, suggesting that maybe the way the gut microbiome interacts with the immune system is different after adversity. There’s a lot that we need to explore in the future.”
The investigation also revealed that some kinds of behavioral and mental health problems were linked to an abundance of certain species in the gut microbiome. While none of these species were the same ones related to adversity in this study, some have been associated with adversity in previous research and could thus perform similar functions.
Since the brain-gut microbiome connection develops rapidly during infancy, it is likely that changes caused by adversity may significantly impact children’s socioemotional development. Further research in fields such as nutritional psychiatry is needed to assess how changes in diet could improve the gut microbiome and, consequently, physical and mental health.
“The microbiome gets a lot of attention and is very exciting, but it really is just one piece of the large and complicated puzzle of human health,” said senior author Bridget Callaghan, an assistant professor of Psychology at UCLA.
“Our study is part of a growing body of research showing the effects of early exposure and transgenerational experience on the microbiome. When we understand how experiences of hardship can influence the gut microbiome, we can then try to manipulate diet, supplements, and lifestyle to make positive impacts on an individual’s gut microbiome and broader developmental trajectory.”
The study is published in the journal Proceedings of the National Academy of Sciences.
The gut microbiome refers to the community of microorganisms, including bacteria, fungi, viruses, and other microbes, that live in the digestive tracts of humans and other animals. These organisms play a critical role in health and disease, and research into the gut microbiome is an active and rapidly expanding field.
A healthy gut microbiome is diverse, containing many different types of organisms. This diversity helps to protect against disease by competing with harmful bacteria and other microbes for resources.
The gut microbiome assists in the digestion of food, particularly substances that the body can’t digest on its own, such as certain types of fiber. These microbes can break down these substances and convert them into useful products, such as short-chain fatty acids.
The gut microbiome plays a crucial role in the development and function of the immune system. Certain types of bacteria in the gut are known to interact with immune cells and influence their activity.
Emerging research suggests that the gut microbiome might also have an impact on mental health. This connection, often referred to as the “gut-brain axis,” could potentially influence conditions such as depression, anxiety, and autism, although more research is needed in this area.
Imbalances or changes in the gut microbiome, known as dysbiosis, have been linked with a number of health conditions, including inflammatory bowel disease (IBD), obesity, cardiovascular disease, and even certain types of cancer.
Probiotics are live bacteria and yeasts that are beneficial for your health, especially your digestive system. Prebiotics are types of dietary fiber that feed the friendly bacteria in your gut. Both can help maintain a healthy gut microbiome.
Scientists are exploring the use of the gut microbiome in personalized medicine, as individual differences in the gut microbiome can influence how people respond to certain drugs and treatments.