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What things in our environment have an effect on the microbes living within us? We now know that gut microbes are important for our health in many ways, and that thousands of species of bacteria, as well as viruses, fungi, and other microbes normally live in a healthy person's gut. We refer to these microbes as the human microbiota or human microbiome. When the community of gut microbes is thrown out of whack (dysbiosis) there can be a number of negative health effects, including diseases. Researchers are just learning about all the microbes within us and their importance in health and disease. [See all posts on the human microbiome.]

Past posts have discussed such things as antibiotics, emulsifiers, different foods and diets, heartburn drugs, etc. having an effect on the human microbiome, but what else? A recent study from China reviewed some environmental pollutants and their effects on gut microbiota - as shown in both human and animal studies. They reviewed studies on antibiotics, heavy metals (arsenic, cadmium, lead), persistant organic pollutants or POPs (organochlorine pesticides, polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers, and polycyclic aromatic hydrocarbons or PAHs), pesticides (permethrin, chlorpyrifos, pentachlorophenol, epoxiconazole and carbendazim, imazalil), emulsifiers, nanoparticles (e.g., silver nanoparticles), and artificial sweeteners. They found that all these environmental pollutants had effects on gut microbes - with some effects lasting for years. Their conclusion: gut microbes are very sensitive to drugs, diet, and environmental pollutants. By the way, notice that popular food ingredients such as emulsifiers and artificial sweeteners were considered "environmental pollutants" by the researchers.

Excerpts from Environmental Pollution: Effects of environmental pollutants on gut microbiota

Environmental pollutants have become an increasingly common health hazard in the last several decades. Recently, a number of studies have demonstrated the profound relationship between gut microbiota and our health. Gut microbiota are very sensitive to drugs, diet, and even environmental pollutants. In this review, we discuss the possible effects of environmental pollutants including antibiotics, heavy metals, persistent organic pollutants, pesticides, nanomaterials, and food additives on gut microbiota and their subsequent effects on health. We emphasize that gut microbiota are also essential for the toxicity evaluation of environmental pollution. In the future, more studies should focus on the relationship between environmental pollution, gut microbiota, and human health.

Thousands of species are found in the gut microbiome, and the majority of these species belong to six bacterial phyla: Firmicutes, Bacteroidetes, Actinobacteria, Proteobacteria, Fusobacteria, and Verrucomicrobia (Eckburg et al., 2005). Gut microbiota are highly dynamic and have substantial interindividual and intraindividual variation....The gut microbiota are very essential for host health. They participate in the regulation of many physiological functions. The gut microbiota reside in our intestinal mucus layer and even participate in shaping the mucus layer (Jakobsson et al., 2015). They help us to digest food (such as fiber); synthesize vitamins and amino acids (Spanogiannopoulos et al., 2016); play very important roles in energy metabolism and storage, immune system modulation, growth, and neurodevelopment; and can even regulate our behavior.... The occurrence of many diseases is correlated with altered gut microbiome composition (Lange et al., 2016). Gut microbiota dysbiosis is considered to be a potential cause of obesity (Cani et al., 2007; Fei and Zhao, 2013). However, gut microbiota are very sensitive to drugs, diet, and environmental pollutants.

Although most environmental pollutants do not directly target gut microbiota, some pollutants can enter the body and interact with the gut microbiota through different pathways. A number of previous studies have shown that exposure to environmental pollutants can alter the composition of the gut microbiome, leading to disorders of energy metabolism, nutrient absorption, and immune system function or the production of other toxic symptoms (Jin et al., 2015c; Zhang et al., 2015b). In the present review, we conclude that different kinds of environmental pollutants can induce gut microbiota dysbiosis and have multiple potential adverse effects on animal health

Heavy metals in the environment have become a severe health risk in recent years (Liu et al., 2016a). As a common form of environmental pollution, heavy metals are associated with a wide range of toxic effects, including carcinogenesis, oxidative stress, and DNA damage, and effects on the immune system..... Recently, several studies have stated that heavy metal exposure could also lead to gut microbiota dysbiosis, indicating that study of gut microbiota provides a new approach to analyze the mechanisms of heavy metal toxicity

Immune system function is tightly coupled to our gut microbiome. Gut microbiota and their metabolites can interact with both the innate immune system and the adaptive immune system (Honda and Littman, 2016; Thaiss et al., 2016).... Alterations in the gut microbiome can disrupt the balance between the host immune system and gut microbiota, induce immune responses, and even trigger some immunological diseases. Furthermore, immune system imbalance may influence the microbiota metabolites. For example, trimethylamine, which is absorbed from food by gut microbiota, can induce atherosclerosis (Chistiakov et al., 2015).

Image result for farm, wikipedia A thought-provoking article by Heiman and Greenway was just published in the journal Molecular Metabolism making the case that changes in farming practices over the last 50 years have resulted in decreased agricultural diversity which, in turn, has resulted in decreased dietary diversity, and that the reduction in dietary diversity has changed and decreased the richness of the human gut microbiota (microbes living in the gut). And meanwhile, during the past 50 years, the rates of obesity, type 2 diabetes, and inflammatory bowel diseases sharply increased - and in each of these conditions there is a reduction of the gut microbial diversity. Similar views have also been stated by others in the field of microbiology.

The thinking is that the more diverse the diet, the more diverse the gut microbiome (and healthier), and the more it can adapt to disturbances. Heiman and Greenway state: "Unfortunately, dietary diversity has been lost during the past 50 years because of economic pressures for greater food production to support a growing world population.... Of the 250,000 to 300,000 known edible plant species, humans use only 150 to 200...Today, 75 percent of the world's food is generated from only 12 plants and five animal species."

Also, agricultural practices of using antibiotics as growth promoters for poultry, swine, and cattle further harm the human gut microbiome when the meat is ingested by humans, and pesticide residues on crops ingested by humans may have gut microbiome effects. Even emulsifiers, used in processed foods, reduce microbial richness. Every time a person goes on a certain diet (vegan, Paleo, etc) or makes dietary choices in which some foods are eliminated, it makes it easier for some microbial species, and gives them a competitive advantage over other gut microbes. From Science Daily:

Reduction in dietary diversity impacts richness of human gut microbiota

Changes in farming practices over the last 50 years have resulted in decreased agro-diversity which, in turn, has resulted in decreased dietary diversity. The significant impact of this change in dietary richness on human health is an emerging topic for discussion

Heiman and Greenway describe how the reduction in dietary diversity has changed the richness of human gut microbiota, the community of microorganisms living in the gut. The researchers point out that healthy individuals have diverse gut microbiota and many of the common pathologies of the 21st century, including type 2 diabetes, obesity and inflammatory bowel disease, are associated with reduced microbiotic richness.

Gut microbiota function as an endocrine organ, metabolizing specific nutrients from the diet and producing specific substances that act as metabolic signals in the host. It follows then that highly specialized diets will change the landscape of the gut microbiome over time. In fact, it takes only a few days of changing diet to alter the microbiotic makeup of the human gut. And if the dietary change involves elimination of one or more macronutrients (think Atkins or Paleo or vegan), humans are essentially selecting for some microbiotic species over others.

The importance of microbiota diversity cannot be overstated. They produce an abundance of important molecules for the host and with increased variation comes increased adaptability and an increased range of physiological responses. "The greater the repertoire of signals, the more likely is the ability to maintain homeostasis when dietary intake is perturbed," explain Heiman and Greenway. "Furthermore, because each particular macronutrient has the potential to be metabolized by microbiota into unique metabolic signals, the greater the variety in signals, the greater the variety of responses possible."

  Children exposed to insecticides (pesticides) at home have an increased risk of developing leukemia or lymphoma, a new review finds.The analysis, of 16 studies done since the 1990s, found that children exposed to indoor insecticides had an elevated risk of developing the blood cancers. There was also a weaker link between exposure to weed killers and the risk of leukemia. There is also evidence from studies linking pesticides with neurological consequences, such as lower IQ and attention deficit hyperactivity disorder.Note: insecticides and weed-killers (herbicides) are both pesticides. The article also gives some non-chemical approaches to treating pests with non-chemical means. From CNN:

Report: Pesticide exposure linked to childhood cancer and lower IQ

Pesticide use in homes may increase the risk of children developing leukemia or lymphoma, a new report suggests. Researchers combined data from 16 earlier studies that had compared pesticide exposure between children who developed leukemia or lymphoma and those who did not. These studies estimated the level of insecticides and herbicides both inside the home and in the yard and outdoor residential space.

The researchers concluded that children who had been exposed to insecticides indoors were 47% more likely to have leukemia and 43% more likely to have lymphoma. Although leukemia and lymphoma are rare -- leukemia affects about five in 100,000 children in the United States -- they are among the common types of childhood cancers. "Childhood cancers are increasing year by year in this country....

This analysis "is confirming that pesticides may play a role, possibly a significant role, in the development of childhood leukemia and lymphoma," Lu said. However, he added that it is hard to say at this point if exposure to these chemicals is definitely a risk factor for these cancers.The association between pesticides and cancer risk is not necessarily limited to leukemia and lymphoma, either, Lu said. Pesticide exposure may also drive up the risk of other types of cancers, such as prostate and bladder, but they have not been studied as much, and are more difficult to research because they take longer to develop, he said. If childhood pesticide exposure helped trigger the onset of these other cancers, they might take many years, possibly into adulthood, to manifest.

The fact that the study found an association between only indoor use of insecticides and increased rates of cancer makes sense, Lu said, because there is less fresh air indoors to dilute the chemicals. And insecticides could be particularly damaging because they are sprayed around the home, whereas herbicides are usually used only around plants, he said. Children can be exposed to pesticides by breathing them in or eating them, Lu said. Chemical residues linger on surfaces where children play or spend time, and they may get them on their hands and put their hands in their mouths. In general, children younger than age 12 appear to be most vulnerable to the possible cancer-causing effects of pesticides.

Other research has suggested a link between parents who are exposed to high levels to pesticides at work, such as through farming, and increased rates of cancers such as leukemia and lymphoma, both in these adults and their children.....In the case of how insecticides could be causing cancer, it may be that the same ingredients that kill insects could be causing genetic mutations in blood cells that lead to leukemia and lymphoma, Lu said.

In the meantime, parents can take precautions to reduce their exposure to pesticides. The most effective way is to prevent pests in the first place, by cleaning up old food, and repairing cracks and crevices through which insects can enter, Lu said.If the pests have already taken over, try non-chemical means first to wipe them out, such as using diatomaceous earth, a powder made from fossilized earth that dries out insect exoskeletons, Lu said. If parents feel they have to use chemicals, opt for bait strips rather than sprays that get everywhere, Lu said.

Some of the studies that Lu and his colleagues included in their analysis suggest that rates of cancer were highest among children who were exposed in the womb and among those whose parents were exposed before they were conceived. "Women who are pregnant or intend to become pregnant can avoid home insecticide application," said Roberts of the Medical University of South Carolina.

Although it is too soon to say unequivocally whether pesticide exposure increases the risk of childhood cancers, there is stronger evidence connecting these chemicals with neurological consequences, such as lower IQ and attention deficit hyperactivity disorder, Karr said.

Pesticide exposure has also been linked to headaches, nausea, skin irritation and other symptoms, according to an American Academy of Pediatrics policy statement on children's exposure to pesticides, which Roberts and Karr wrote. A study to be published in the October issue of Pediatrics along with Lu's research raises the possibility that high doses of pesticide may even lead to sudden infant death. A post-mortem analysis by researchers in Italy of a 7-month-old girl who had died in her sleep revealed high levels of a pesticide called DBNP in the brain tissue. The girl may have inhaled the chemical after her father sprayed insecticide around the house to kill flies in the two weeks before her death. "This single incident would be reflective of acute toxicity. Pesticides play a role in acute and chronic health problems depending on the level of exposure," Lu said.

From Medical Xpress;  Home pesticide use tied to child cancer risk

Children exposed to insecticides at home may have a slightly increased risk of developing leukemia or lymphoma, a new review finds.The analysis, of 16 studies done since the 1990s, found that children exposed to indoor insecticides had an elevated risk of developing the blood cancers. There was also a weaker link between exposure to weed killers and the risk of leukemia....."Despite the questions, Lu said he thinks it's wise to act now, by limiting babies' and children's exposure to chemical pesticides—especially the indoor insect killers that this study linked to leukemia and lymphoma.

Overall, children who'd been exposed to any indoor insecticides were 43 percent to 47 percent more likely to have leukemia or lymphoma, the findings showed. Outdoor insecticides were not linked to the cancers.Kids exposed to weed killers, meanwhile, had a 26 percent higher risk of leukemia, the investigators found.