Study finds effect of arsenic on infant gut microbiomes

by Lex Kang | 9/14/18 2:25am

New Hampshire residents using private wells, especially households with pregnant women or infants, should be attentive to the possibility of arsenic contamination. On Aug. 22, researchers at the Geisel School of Medicine published their findings on the effect of arsenic exposure on infants’ gut microbiomes, the microbes and bacteria occupying the gut. The study found that infants’ gut microbiomes shift after arsenic exposure, leading to potential health risks.

Epidemiology professor and the study’s lead author Anne Hoen said that the decision to investigate the effects of arsenic was partially inspired by preceding studies in the field that reported mice having changes in their gut microbiomes after ingesting drinking water contaminated by arsenic, a substance “known to be a powerful anti-microbial substance.” New Hampshire also has “a known problem with arsenic-contaminated drinking water” because arsenic occurs naturally in the soil and the state has a significant population of people that use private, unregulated well systems, Hoen added.

Geisel pediatrics and epidemiology professor and study co-author Juliette Madan added that because arsenic releases antibiotics that kill microbes, the research team was “interested in understanding how arsenic related to gut microbiome composition in this vulnerable population [of] developing babies and how that might relate to [their] health outcomes for the long term.”

After years of analyzing the data collected from infants enrolled in the New Hampshire birth cohort, Madan noted that the study, which examined both the infants’ urine to check for the level of arsenic exposure and stool samples to check for gut microbiome composition and condition, showed that infants exposed to arsenic, even very trace amounts, had different gut microbiome compositions than infants who were not.

“Arsenic kills microbes,” Madan said. “[Arsenic] has been used as an antibiotic in the past, even at low levels. And what we found was that babies that have arsenic exposure in their water in New Hampshire have an overall gut microbiome community that looks different from babies who do not have arsenic exposure.”

Hoen added there is a difference between babies who were formula-fed and babies who were breastfed. According to her, arsenic’s effects on the babies’ gut microbiomes remained with formula-fed babies but not in exclusively breastfed babies, as arsenic does not contaminate breast milk regardless of the mother’s arsenic exposure.

However, Geisel epidemiology professor and study co-author Modupe Coker added that despite the findings of the study, it can not be concluded that breastfeeding is inherently safer or superior to using formula because there are still many factors that have not yet been explored.

“[The study isn’t showing that] automatically, formula-fed children will do worse,” Coker said. “That’s not true. What we’re saying is that maybe the body compensates [for] some things, maybe a child is exposed [to arsenic], but they have a stronger immune system.”

Though the differences in the gut microbiomes of infants exposed to arsenic were not explicitly characterized as good or bad, Madan said that the differences could be a cause of health concern as they have “the potential for causing risk of disease,” particularly in infants.

“When babies are born, they don’t have really many microbes in and on their body,” Madan said. “They’re acquiring microbes over the first year of life. Those microbes are responsible for a large proportion of innate and adaptive immune training that relates to allergy risk, infection risk, cancer risks for autoimmune disease risk, obesity risk — you name it.”

Madan added that the study’s conclusions may have implications in broader contexts. For example, there could be a potential connection to cancer in adults, the EPA’s guidelines for acceptable arsenic levels may be too liberal to fully prevent detrimental health effects on individuals exposed to the toxin, and developing countries have even higher arsenic exposure rates, she said.

For the future, Hoen said that the research team wishes to investigate the impacts of exposure to other common environmental contaminants while considering complicating factors such as diet, as well as following up on the health of this study’s babies in their childhood.

“We’re following the babies [that we studied] to look at their early health outcomes, so whether they’re diagnosed with an allergy, or asthma, or ear infections, or respiratory infections,” Hoen said. “We’ll be looking [at how the] gut microbiome composition, shortly after birth, is associated with risk for those different health outcomes.”

Hoen noted that one of the limitations of the study is that the mothers enrolled in the cohort were generally healthy and gave birth to similarly healthy babies, meaning that the study is unlikely to yield findings on rarer health conditions.

Madan said that the results of the study indicated the importance of New Hampshire residents with private wells having their wells tested annually and after pregnancy and childbirth, especially because both environmental toxins and nutrients found in wells can change over time.

“The recommendation is to test your well once a year … so that you know [if] there’s been any change in bacteria [or toxins] in the well,” Madan said. “[With] that information, you can set your filters to address those exposures. Unfortunately, in New Hampshire, wells are not regulated, so it’s up to the homeowners to address that potential environmental risk.”

According to Coker, the study’s conclusions should also lead the public to draw more widespread awareness about environment and health rather than solely about drinking water.

“The takeaway [is] that we generally need to start paying attention to the environment and how it impacts the health of humans,” Coker said. “As a group, we need to pay attention to how [the environment] impacts [health] in infancy and [has] long term outcomes at any point in life. It’s something that we as the public need to pay attention to.”