Exposure to chemicals that pollute the environment cause changes in the gut microbiome and are linked to problems with the immune system, changes in fat and carbohydrate metabolism and neurological and behavioral issues, suggests an analysis of more than 100 studies.
The researchers noted that the effects of exposure to environmental chemicals on the gut microbiome—including bisphenols, phthalates, persistent organic pollutants, heavy metals, herbicides and pesticides—was influenced a lot by gender and age in the organism that was exposed. In addition to studies in humans, they also looked at studies of microbiome changes in rodents, fish, dogs, chickens, cows, and honey bees.
Writing in the journal Toxicological Sciences, the scientists say that an important question that still needs to be answered is whether microbes in the gut are able to protect us from these chemicals to any degree, as this was not adequately addressed in the studies they reviewed.
It has been well established that our gut bacteria or ‘microbiome’ has a big influence on how healthy we are and if we have more ‘bad’ microbes than good then it can often have an adverse effect on our health.
Environmental factors such as what we eat and how much exercise we do are known to influence the health of our gut microbiome, but the impact of toxic chemicals and pollutants in the environment is less clear.
“More than 300 environmental contaminants or the metabolic byproducts of those contaminants have been measured in human urine, blood or other biological samples,” said Jodi Flaws, PhD, corresponding author on the study and a professor at the University of Illinois at Urbana-Champaign in the US.
“Chemicals such as bisphenols, phthalates and some pesticides, persistent organic pollutants and heavy metals can alter hormone metabolism and are associated with adverse health outcomes.”
Bisphenols such as bisphenol A are used to make food packaging and containers. They are endocrine disruptors that cause hormonal problems and are known to be detectable in the urine of over 90% of adults in the US.
These chemicals seem to have a worse impact on males than females and a key effect observed in at least one study in mice was increased levels of Methanobrevibacter bacteria in gut of male animals. These bacteria increase an animal’s ability to extract energy from food and the researchers believe this could at least partly explain the weight gain seen in those exposed to the chemical.
Phthalates are plasticizers and are found in many different household products including food packaging, toys and detergents. They also disrupt normal hormone function.
In a study in newborn babies, exposure to phthalates was linked to changes in the gut microbiome that impacted their response to vaccination, indicating a possible adverse impact on the immune system in later life. Another study in mice showed that production of butyrate, a fatty acid produced by gut bacteria that is needed for healthy colon cells, was inhibited by exposure to these chemicals.
Persistent organic pollutants such as polychlorinated biphenyls take a long time to break down – some have been banned due to the negative effects they have on health, but reasonably high levels can still be found in the environment. The effects of exposure to these chemicals varies, but exposure changes the gut microbiome and has been linked with increased gut permeability, intestinal inflammation and cognitive problems.
These are just some examples of the effects of exposure to these environmental chemicals on gut microbes.
“All of these data together suggest that exposure to many of these environmental chemicals during various stages of life can alter the gut microbiome in ways that influence health,” commented Karen Chiu, a co-author on the study, who is currently completing a PhD at the University of Illinois at Urbana-Champaign.
