Mothers’ hardship during their own childhood or pregnancy affects their 2-year-old children’s gut microbiomes, according to a team of scientists led by UCLA psychologists.
The children’s microbiomes showed small to medium changes, making this research the first to demonstrate the transgenerational effects of adversity on the human gut microbiome.
Research has increasingly linked the gut microbiome to brain and immune functioning. The researchers believe that changes in the gut microbiome are among the ways that hardship impacts children’s socioemotional development.
Prior studies with rodents have shown that prenatal stress disrupts maternal vaginal and gut microbiomes. As infants acquire their first gut microbes during birth, their mother’s microbiome is the foundation.
Previous research in humans has indicated that stress experienced by infants in the womb and the mother’s psychological distress influence the infant microbiome soon after birth. While it was known that the effects of prenatal stress on rodent microbiomes persist into adulthood, it was unclear how long after birth these disturbances remain in humans or if they affect the next generation.
The study examined the consequences of maltreatment during mothers’ childhood, anxiety during pregnancy, and their children’s exposure to life stress events in 450 mother-child pairs in Singapore when the children were 2 years old. Researchers asked mothers about abuse or neglect they experienced as children and screened for anxiety during the second trimester of pregnancy.
Interviews with the children’s primary caregivers were conducted to learn about their experiences of stressful events, as well as their behavior and health during their first two years of life. Stool samples were collected from the children, and family income was controlled for as a proxy for childhood adversity.
Children whose mothers reported higher levels of anxiety during pregnancy had microbiomes where the populations of microorganisms were more evenly distributed, a measure called “evenness” that had not been observed before. Typically, the populations of various species in the gut vary, with some species being more abundant than others. However, in this study, those differences were less prominent, and populations were more similar in size.
Children who experienced stressful life events after birth also had less genetic diversity in their gut microbes. This means that the microbes in each child’s gut were more closely related than they typically are.
While more experiences of adversity were associated with less microbial genetic diversity in each child, the amount of adversity did not seem to affect the similarity of gut microbiomes between children. There was still variation among them.
“There are many questions surrounding 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 2 years old,” explained Francesca Querdasi, the lead author of the study and a UCLA doctoral student.
She added, “But many of the species we found to be related to adversity are known to interact with the immune system, suggesting that maybe the way the gut microbiome interacts with the immune system is different after adversity. There’s much more to explore in the future.”
The researchers also discovered that certain behavioral and mental health problems were associated with an abundance of specific species in the gut microbiome. Although these species were not the same as those related to adversity in this study, past research has linked some of them to adversity, suggesting that they may perform similar functions.
The brain-gut microbiome connection rapidly develops during the first two to three years of life, and it is likely that the changes caused by adversity demonstrated in this study have an impact on children’s socioemotional development.
A field of study called nutritional psychiatry, which explores how dietary changes can affect mental health, is developing as scientists learn more about the brain-gut microbiome connection.
“The microbiome receives a lot of attention and is very exciting, but it is just one piece of the larger and complex puzzle of human health,” stated Bridget Callaghan, a senior author of the paper and a UCLA assistant professor of psychology.
She continued, “Our study adds to the growing body of research that shows the effects of early exposure and transgenerational experiences on the microbiome. Understanding how hardship experiences can influence the gut microbiome allows us to explore ways to make positive impacts on an individual’s gut microbiome and overall developmental trajectory through the manipulation of diet, supplements, and lifestyle.”