Interview Summary

This topic is so important, and you just hear time and time again from experts all around the world how profoundly the microbiome was influencing our health and how many factors affect the microbiome. But now to think about this generational matter that you addressed in your research is interesting and scary, in a way. Let’s first start off with this question about how you studied these mothers and the children. What were you looking for?

The goal of the study was to see how experiences of adversity or hardship across two generations might be related to the composition of the children’s gut microbiome, or in other words, which microbes were living in their guts. So, for this paper, I worked with colleagues at the University of California-Los Angeles, as well as a team of scientists in Singapore who are currently conducting a big birth cohort study called Growing Up in Singapore Towards healthy Outcomes, or GUSTO for short. That study has thousands of mothers and families enrolled but, in this paper, we focused on around 450 families who had data on what we were interested in – the mother generation, as well as her child generation. We specifically wanted to study the children when they were around two years old because the gut microbiome develops really rapidly during that period from birth until around two years of age.

In this study, we asked mothers to tell us about three different kinds of adversity. First, their history of maltreatment. That would be things like abuse and neglect in their own childhood and then kind of moving forward in time, any symptoms of anxiety during their pregnancies. Then moving forward again into the children’s generation, their children’s exposure to stressful life events. So, things like their parents’ divorce or the death of a family member from birth till two years of age. At two years of age, we collected poop samples to analyze the children’s microbiomes. Then we also asked families to report on their children’s social emotional problems. So, things like aggression, sadness, issues with attention on when they were two years old and then again at age four because we really wanted to see also how their microbiomes were related to their early childhood health.

I’m eager to hear what you found but first, let me say I’m impressed that you even bothered to ask this question because one wouldn’t think that traumatic experiences decades ago in the life of a mother would affect the microbiome of a child today. So, tell us, please, what did you find?

We found that each of the adversity experiences that we asked about – so abuse or neglect that the mother experienced in her own childhood, the mothers’ symptoms of anxiety during pregnancy, as well as children’s experiences of stressful events in their early life – all of those seem to have an impact on the children’s gut microbiomes. Specifically, we found something interesting, which was that some of the microbes that seem to be related to adversity we think that they might perform similar functions to those that we found were related to the children’s social emotional health, both at two years and then at four years of age. We think that those microbes probably play a role in regulating the immune system and inflammation. Our findings kind of hint that maybe disruption to some immune-related functions within the gut could help explain how some children go on to develop mental health struggles after they experience adversity. And how that intergenerational experience of adversity shows up in subsequent generations.

Like I said, it’s hard to imagine that things so distinct in timing can have such a big impact. How is it possible that adversity experienced by a mom in her own childhood could affect her child now in terms of the microbiome?

That is pretty surprising. You think that it’s so far in the past, but it’s really striking that it does still appear to have an impact. This study was the first one to find evidence for that in humans. There have been studies in animal models, researchers that work with rats and mice, and there was evidence the mom’s experiences during childhood affect their children’s gut microbiome. There is other research that studies this phenomenon, called intergenerational transmission of adversity, and that’s when trauma, chronic stress, adversity, those kinds of experiences experienced in one generation have impacts on the following generations. Even in those who have never directly experienced the event. Research has brought up many possible explanations for why that might happen, from changes to gene expression after adversity to changes to the parent’s health and behaviors. In terms of the microbiome specifically, it’s possible that the mother’s health or underlying biology and physiological response to stress was affected by that adversity that she experienced in some way. And that shaped her child’s development in terms of brain or stress response systems during her pregnancy. Then, because the microbiome is really connected to other biological systems that had an impact on the microbiome, the mother’s microbiome plays a big role in shaping the child’s initial microbiome during birth, and then after birth in terms of contact with the child and breastfeeding, things like that. The bottom line is that the mother’s microbiome was affected by her adversity and then directly shaped the child’s microbiome.

A fascinating set of possibilities you’re talking about. Let me ask you a down in the weeds question. How can you isolate the impact of the adverse childhood experiences in the mother in terms of its impact in the microbiome from other things that just might co-occur with the adverse childhood experiences, social disparities, economic disparities, health disparities in general and things like that?

That is definitely really challenging to do, and we did that to some degree in our study. There’s definitely a lot of future research that needs to be done to tease apart the different factors that might play into that relationship between the mother’s adversity in childhood and her child’s microbiome. But we did account for the mother’s socioeconomic status in terms of the family’s income, and we also accounted for the birth mode of the child, so whether the child was born by C-section or vaginal birth. So, in that sense, we tried to isolate the impact of the mother’s adversity.

That makes sense. It sounds like you took care to address that issue. Now let me ask a question about what can be done given this relationship you found. Is there anything that can be done to disrupt this connection? One might think perhaps if the mother had eaten a diet that was specifically designed to optimize the microbiome, would that help, for example?

That’s a really important point. There are many things that impact the gut microbiome in addition to adversity experiences. Diet, other things in the environment like exposure to nature and other people, the urbanity of your living environment and overall stress levels as well. That also highlights that many things can be done, both on an individual and societal level to promote a healthy gut microbiome and possibly counteract or mitigate impacts based on adversity. We’re very far away from knowing exactly what the perfect way is to address this because there’s just so much more that we need to know about the gut microbiome. But there are some general things. We know that eating a variety of foods that have a lot of fibers like fruits and vegetables, that’s good for your gut microbiome. So, policies that make those foods more widely accessible and affordable. And then things that can help you manage stress in a healthy way. So, meditation, exercise, really strong supportive social relationships, as well as policy supports for families that reduce financial stress and precarity. Then, in terms of focusing on specifically early life policies that allow parents the time to form positive relationships with their kids, like parental leave and things that help maximize the mother’s health broadly. So, affordable perinatal care can set the child up for the best possible start to life. Those are changes that would promote microbiome health broadly in addition to overall health.

Those things all make sense. And the good news is that every one of those things you mentioned would have health and mental health benefits way beyond the microbiome. So, good reason to focus on those things. Now let me ask you one final question. Are you working on follow-up studies to this?

Yes, we are. So, in that study, as I mentioned, we were looking at microbiome composition, which means which microbes live in the gut. We found evidence suggesting that immune functioning was really important, but the methods that we used were not able to test the function of the microbes directly. So, we’re following up on this work by looking at the same questions of how adversity experiences impact the microbiome but looking at function of the microbes directly. So, in this group of families that we studied, as well as others, I’m also interested in looking at how adversity might impact communication between the immune system and the gut microbiome. The gut microbiome is really intimately connected to other systems. For example, there’s many connections between the gut microbiome and the brain and the brain and gut microbiome influence each other. I’m looking at communication between the gut microbiome and brain as well. So, trying to get a more complete and whole-body picture of the processes that are affected by adversity and if those changes relate to mental and physical health and kind of the specifics of how that works and I really hope that that work will open up new ways to treat and prevent health problems in families exposed to adversity.