Gut Bacteria May Link Maternal, Child Weight

Really good epidemiologic research gives insight
into pathophysiology. When John Snow – no, not that Jon Snow,
this John Snow – mapped a cholera outbreak to the Broad Street pump, we learned something
about how the disease was spread. You know something, John Snow. Anyway this week we’re looking at a modern
epidemiologic study examining the problem of childhood obesity – tracing the disease
to its source, so to speak. The paper by Anita Kozyrskyj (Kuh-ZER-SKee)
and colleagues tries to untangle a complex web of exposures. Dr. Kozyrskyj was nice enough to walk me through
some of the more complicated analyses. They looked at 935 mother-child pairs from
the Canadian Healthy Infant Longitudinal Development Cohort. The primary finding is not particularly shocking. Overweight and obese women were more like
to have children who were overweight and obese at age 1 or 3 years. But the plot quickly thickened. They found that when an overweight woman delivered
vaginally, the risk of overweight in the child was three times higher than normal. But the risk was 5 times higher than normal
when the woman delivered via c-section. This association persisted even after adjustment
for multiple other factors. There seemed to be something about C-section
that increased the risk of childhood obesity. Dr. Kozyrskyj wondered if the obesity effect
could be mediated in part by the gut microbiome. They had gotten stool samples from all these
kids at around 3 months of age. Now, microbiome studies have exploded onto
the scene recently, and it seems clear that the interplay between our bodies and the trillions
of bacteria that live inside us have important implications for health and sickness. The newborn gut is probably close to sterile. But bacterial colonization starts happening
at birth, essentially. And passage through the birth canal during
vaginal delivery may be an important source of bacterial inoculation. Could this explain the difference in obesity
rates between those kids born vaginally and those via c-section? What the researchers found was that the abundance
of a particular family of bacteria called lachnospiracae do in fact mediate part of
the relationship between maternal weight and child weight. Putting some numbers to it, overweight women
who delivered via c-section were twice as likely to have kids with high levels of lachnospiracae,
and kids with high levels of lachnospiracae were twice as likely to end up overweight
or obese. This is all preliminary work. We don’t have a smoking gun. But the study is important because it lends
support to a really interesting hypothesis: that the initial inoculation with a set of
bacterial flora has long-lasting effects. So the next time someone says to you: “you
have your father’s eyes”, you just shoot back “yes, but my mother’s microbiome”.

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