More and more research these days suggests we’ve gone too far with our drive to eliminate germs, and that kids could use a little dirt and grime to improve their own health. A new paper published in the Canadian Medical Association Journal on Monday doubles down on that idea, and suggests that infant exposure to common household cleaners could give rise to obesity later in life. And it all comes back to one of modern medicine’s new favorite obsessions: the gut microbiome.
“You have this set of microbes in your gut that you’re dependent on, for a large number of things you take for granted,” says study coauthor James Scott, a researcher who studies environmental health at the University of Toronto. “It’s interesting to see that they’re subject to influences in your environment in ways you’ve never thought.”
The jury is still out on exactly how gut bacteria are actually capable of making us fat or keeping us thin. But the evidence is already here that environmental factors can affect our weight gain, and if gut bacteria do indeed play a role in how we burn fat and keep weight off, then it’s worth investigating what sorts of external factors mediate this relationship.
“The gut microbial community that establishes inside of us is very important in regulating how we use the foods that we eat,” says Scott. “When we eat stuff, we think that we’re feeding ourselves, but mostly we’re feeding microbes. And what the microbes do with it can cause us to use energy differently,” affecting how we store fat and how robustly our metabolism runs.
This is exacerbated by the fact that baby microbiomes are much more vulnerable to changes. “When a baby is born, there really isn’t much of a bacterial community in its gut,” says Scott. It can take up to a year for that bacteria to settle down and make a home for themselves in our intestines, and this process is affected by everything from illness and treatment with antibiotics, to feeding with formula or breastmilk.
“Once you have an adult microbiome, it’s a fairly durable, permanent thing,” says Scott. Relatively speaking, anyway—diet and environmental changes can cause shifts even in grown-ups. “But it’s very fragile over that first year of life, especially in the first 100 days.” Scott and his colleagues were interested in gauging whether household cleaners, often antagonistic to bacteria, could have a tangible impact on the gut flora living inside of us during this delicate period.
The latest findings are actually part of a much more extensive research project focused around the Canadian Healthy Infant Longitudinal Development (CHILD) birth cohort: a database of health, medical, and behavioral data taken from over 3,500 Canadian children starting when they were fetuses, originally to determine the environmental factors that lead to asthma and allergies in kids. Over the years, the study—now 10 years old and comprising more than 40 researchers—has grown tremendously in scope, creating opportunities to investigate childhood obesity.
For this particular study, Scott and his team collected and analyzed stool samples from 757 CHILD cohort infants when they were 3 to 4 months old to profile each baby’s gut microbiota. The team also took an inventory of each infant’s household for cleaning products to gauge how much those children were exposed to disinfectants and multipurpose chemicals, and also measured body mass index (BMI) at age 1 and age 3 as a measure of obesity.
Taken together, the team found that children living in homes where antimicrobial products were used at least weekly during infancy had higher BMIs at age 3 than children living in homes with less frequent disinfectant use and where cleaning products were billed as “eco-friendly” (i.e. non-antibacterial). These infants with higher BMIs possessed microbiota profiles that seemed to correspond with the findings, including lower levels of common gut bacteria like Haemophilus and Clostridium.
The researchers were particularly struck by the fact that children exposed to more disinfectants were twice as likely to have higher abundances of Lachnospiraceae, bacteria associated with higher rates of body fat and insulin resistance in animal studies. “We know it’s an important player in terms of what the mature microbiome will look like,” says Scott. Although there are hundreds and hundreds of species of bacteria living in our guts, Scott says only a small variety wield the greatest influence over what the microbiota eventually looks like.
But don’t get hasty and start throwing out your sprays and wet wipes. There are plenty of reasons to eye the findings with a bit of caution. “One of the drawbacks of our study,” says Scott, “is that we didn’t actually make physical measurements of chemical residues, either in the home environment by analyzing things like dust samples, or within the biology by looking at blood or urine samples.” The study hinges on an assumption that cleaning products in the home were used regularly, but without determining how extensively these products were used. “There may be a sub-population of individuals that we’re misclassifying, who have the products but aren’t using them.” And no distinction was made between specific ingredients, other than whether they were antibacterial or not.
Moreover, the data doesn’t factor in other important influencers of gut bacteria profiles, like diet, antibiotic use, the overweight status of the mother before pregnancy, and more.
Scott himself admits the results “are by no means demonstrative of a relationship” between cleaning products and obesity. There’s simply not enough that we understand about the biological mechanisms that encourage or attenuate gut flora like Lachnospiraceae. “The effect is a fairly weak effect, as far as we can tell. The relationship is significant, but I wouldn’t say they are strongly significant. And that significance doesn’t tell us anything about the nature of the relationship.”
Instead, Scott believes “the results really give us some tantalizing window into what’s happening, and raises the next, really interesting questions. It’s important for us to go back and tease out the mechanisms.” And he thinks the ongoing investigations with the CHILD data gives the researchers the foundation to move forward in follow-up studies.
Ultimately, until we have more data to work with, you should stick with the same sort of cleaning practices most experts promote: disinfecting things as need be, but refraining from going overboard and trying to turn your home into a haven of sterility. It’s never a bad thing for babies and toddlers to get a little dirty once in a while.