Dec. 17, 2019

Do our guts reflect the people around us? How our relationships and our environments change our microbiomes

Our microbiomes — the trillions of micro-organisms that live in and on our bodies — are unique to each of us. But research is showing that our microbiomes are affected by our places, our pets and our people.

We start developing our microbiomes the second we’re born. Over the next few hours and during our first few years, the people and places we’re exposed to shape the trillions of bacteria, viruses and fungi that live in and around our bodies. And over time, we’re finding that the composition of our microbiomes can reflect our relationships.

A baby colonized in the birth canal with their mom’s microbiota will become a toddler who may like to stick the germ-laden TV remote control in their mouth or curl up on the dog bed for a cuddle with Fido. As children grow into puberty, and beyond, they face hormonal changes, may move in with a roommate or two, have intimate relationships, and eventually maybe settle in with a live-in mate. At some point they may have children — and a dog — of their own.

As we move through the different stages of life, our microbiome evolves too. The trillions of organisms may be affected by — or “converge” with — other micro-organisms we encounter in our daily lives.  While we all maintain our own unique microbiomes as we age, researchers are finding that our micro-organisms can shift a little to somewhat align with those we spend time with.

“We can still distinguish our own unique signature even as we move about in these different environments, with different humans or pets that we live with. But we see enough convergence that we can tell who cohabitates with us,” says Dr. Laura Sycuro, PhD, an assistant professor in the Departments of Obstetrics & Gynaecology, Biochemistry & Molecular Biology, and Microbiology, Immunology and Infectious Diseases in UCalgary's Cumming School of Medicine. “We don't really stop looking like our own unique person.”

Sycuro, who is also a member of the Snyder Institute for Chronic Diseases, studies how to better identify the organisms in the microbiome and “harness” them to promote maternal and child health. She says the external influences we encounter as we grow don’t pack as big a punch as our very first exposure to micro-organisms; starting during birth and as an infant and small child. “We have the initial establishment of our own unique microbial signature in the first three years of our life,” she says. “These other effects later in life tend to be less strong than that initial formation.”

Researchers are diving into this this emerging field of study to learn more about how the microbiota in different parts of our body evolve over the course of our lives and how our collection of micro-organisms can shift with the people, pets and places around us.

The changing microbiome

We start aging, of course, the second we’re born. And as we progress from childhood into adulthood we may notice all manner of changes affecting our aging bodies — our skin gets thinner, our lung capacity diminishes and we lose muscle mass, for a start. A new field of study explores how our microbiomes are also affected with aging.  

“Your microbiota starts to look more adult by the time you're three, but that’s very specific to the gut,” says Sycuro. “Other body sites are still choosing and some of that is due to hormones.” There is some data that indicates that as we get older we start to lose some of the vast diversity in our gut microbiota but we still have much to learn about how, specifically, the microbiome is affected as we age.

What we do know for certain is that our microbiome impacts absolutely everything about our bodies — from the moment of fertilization all through our lives and even after we die and our bodies start to decompose. “The level of physiological interconnectedness between us and our microbiome means that there isn't a single biochemical or biological process that we go through at any point in our life — from conception through death and even on either end of those two events — that isn’t affected by microbes,” says Sycuro. 

This includes our hormones. These chemical messengers regulate various systems in our bodies — everything from the stress you feel when you’re running late for an important meeting to massive changes like puberty and menopause.  These fluctuations — throughout the day and throughout our lives — both affect and are affected by the microbiome.  There is not a lot of research yet into how a man’s microbiota interacts with testosterone, the main male sex hormone, but Sycuro and others are studying how microbiota interacts with hormonal changes in women.

Menstruation to menopause

With the onset of menstruation at puberty, there are changes to the genital tissue and the “dense communities of microbes” in the vagina.  Unlike a healthy gut, which has thousands of different strains of micro-organisms, the vagina has only a handful. When a woman hits reproductive age, her hormones help select for a dominate strain, called lactobacillus.

“We know there are dozens of species of lactobacillus, many of which can colonize the human body, but only four species typically are found in the vagina,” says Sycuro. “We don't understand why these species dominate. We know that they're important for protecting pregnancy, keeping that access point free of potential pathogens. Certain vaginal lactobacilli also help protect against sexually transmitted infections, which of course is another type of microbial exchange.”

Sycuro and her lab are researching whether the vaginal microbiota could be used to help prevent sexually transmitted infections (STIs), including HIV. In a collaborative project led by Dr. Alison Roxby, MD, at the University of Washington, they’re looking at women and girls in Sub-Saharan Africa where as many as 7,000 females are infected with HIV every week — adolescents 15-24 years of age are at the highest risk. Because the microbiota in the vagina changes with age and hormones, the age at which a girl or woman first has sex could be very important.

“When people are quite young, their bodies aren't fully mature,” she says. “And they might have a different sort of microbiota at that time. Maybe there are certain factors that put people at greater risk of an STI based on their microbiota.” The researchers are looking for microbial markers that may show who is at a greater risk for an STI and what interventions, if any, could help reduce that risk and prevent infection.

At the end of a woman’s reproductive cycle, in menopause, hormones, vaginal tissues and microbiota all change again. “It’s a tight balance between what happens with our hormones and what happens with our microbiota,” says Sycuro. “When a woman goes through menopause that all goes away and you start to see that there is less lactobacillus in the vaginal niche. Some women still have it but not all do.”

Sharing space as well as micro-organisms

They say that couples that live together for a long time start to adopt each other’s habits, and even look like each other. You may or may not start to look like your mate, but your microbiome will start to share a few of the same bugs. “Whenever you cohabitate with somebody, there is some convergence, some sharing of microbes that happens with some regular frequency. You start to have a little bit of their unique signature on you and they have a little bit of your unique signature on them,” says Sycuro. “You are also engaging with your shared environment. So you're leaving those signatures on all the things in your home and maybe some unique components in your home are impacting on both of you. “

By sharing a home you’re sharing its distinct physical environment — consider a high rise with a balcony versus a main floor surrounded by gardens — and you’re also sharing its internal features; the ventilation system, the chemicals in the material on the couch and even the cleanser used to scrub the tub (Sycuro and others warn against using anti-bacterial products — see eBook). People who live together have microbiomes that reflect all these similar features. 

There is growing evidence that the younger you are, the bigger the role your home plays on your microbiota because it is still developing. “As babies start to engage with their environment, they get that kind of initial exposure to environmental microbes; things in the home they put in their mouth, the things they're climbing on and things they're encountering for the first time,” she says. “We have very specific micro niches in our body with very specific biochemicals. Whatever microbes get there first and inhabit that micro niche or utilize a certain biochemical to its advantage have a selective advantage over other microbes that may be encountered later. This is how we develop that unique signature.”

Dog people have an edge

While pet people love having their particular animal in the house — be it a snake, cat or hamster — those who have dogs around are likely helping their microbiota. Researchers have found that young children who grow up with a dog are less likely to suffer from allergies. And women who are around dogs when they’re pregnant may pass along a lower risk of allergies to their children. Sadly for snake people, research seems to show that only “furry animals” have an effect.

“The essential component about dogs that was identified was that they bring the outdoor environment indoors,” says Sycuro. “And exposure to the outdoor environment is healthy for us.” Early humans spent a lot of time around dirt, and small children were exposed to plenty of soil and other microbes in the natural environment.  “That sort of exposure in Western civilization has now diminished. But the dog brings that indoors and they deposit it on our furniture and our rugs. We get a little bit more exposure which benefits our microbiome and thus, our development.”

More to learn

Researchers have been studying the composition and function of the microbiome in a big way for only a couple of decades. There are decades more of exciting developments to come – looking at how our billions of microbes affect our bodies’ systems and our overall health.

“It's been interesting watching this unfold,” says Sycuro. “When I was trying to decide where to focus my career early on, I had people tell me that I'd missed the boat, and that microbiome was going to be a ‘here and there’ thing by the time I finished my training.”

Instead, over the last 10 years, she’s seen pregnant women and parents start to embrace the knowledge she and other researchers are uncovering — that bacteria play a big role in human reproduction. “Now lots of moms recognize this and they're keen to take deliberate steps to help their babies have healthy exposures to bacteria. People are really starting to understand and buy into it. And our hope is that we develop better and better evidence-based guidelines,” she says.

While she is focused on how the microbiome affects maternal and child health, many other researchers are devoted to discovering more about the gut-brain axis. We’re finding that rather than the brain telling the rest of the body what to do, the bacteria in the gut are communicating with the brain, and having a tremendous effect on both our mental and physical health. There’s every reason to expect that the gut-brain axis also changes with age and some of our relationships, but we just don’t have enough knowledge at this point. “We've only been talking about gut-brain for a handful of years,” she says. “So there's no study that follows people and really captures gut-brain indices throughout life.”

But what we do know, and what Sycuro and other researchers in the field can say with absolute confidence is: “Every single thing about our physiology is impacted by the microbiome.”


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Dr. Laura Sycuro, PhD, is an assistant professor in the Departments of Obstetrics & Gynaecology, Biochemistry & Molecular Biology, and Microbiology, Immunology and Infectious Diseases and member of the Snyder Institute for Chronic Diseases in UCalgary's Cumming School of Medicine. Read more about Laura


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