A new report offers much-needed guidance for research on how the human microbiome might influence the health effects of environmental chemicals. Future research in this field could explain why responses to chemicals vary between animal and human studies and across human populations, according to the authors.

The National Academies of Sciences, Engineering, and Medicine (NASEM) released the report, “Environmental Chemicals, the Human Microbiome, and Health Risk: A Research Strategy,” in December 2017.

The microbiome includes microorganisms that live in and on us, and contribute to human health and disease. (Photo courtesy of Darryl Leja, National Human Genome Research Institute)

The human microbiome consists of a large number of diverse microorganisms that inhabit different parts of the body, such as skin, lungs, mouth, and gut. There is increasing evidence for the microbiome’s importance in a wide range of diseases, including diabetes, asthma, and inflammatory bowel disease. Recent studies have also shown that the human microbiome can metabolize environmental chemicals, and in turn, might be affected by chemical exposure.

“This direct interaction suggests that the microbiome may need to be considered in risk assessment,” said Lisa Chadwick, Ph.D., a health scientist administrator at the Genes, Environment, and Health Branch at NIEHS. Chadwick gave a presentation during an open session of the NASEM Committee on Advancing Understanding of the Implications of Environmental-Chemical Interactions with the Human Microbiome.

“The committee was tasked with identifying high-priority research avenues that would need to be pursued in order to understand how to best incorporate the microbiome into risk assessment,” Chadwick explained.

Three-pronged approach

Chadwick directs grant programs in microbiome–environment interaction, transgenerational inheritance, and is a scientific contact for NIEHS-funded epigenetics studies. (Photo courtesy of Steve McCaw)

Over the decades, the core elements of assessing the health risk of environmental chemicals have remained the same (see related story). To date, no research approach explicitly considers the potential influence of the human microbiome. Therefore, the role of the microbiome in modifying human susceptibility to toxicity at environmentally relevant exposures remains largely uncertain.

To address this knowledge gap, NIEHS and the U.S. Environmental Protection Agency (EPA) sponsored the committee of experts that prepared the new report. The committee’s proposed research strategy focuses on three general topics.

1. Determine whether exposure to environmental chemicals alter the microbiome in ways that influence health effects.
2. Evaluate the effects of the human microbiome on how the body processes the environmental chemicals it is exposed to.
3. Examine the importance of microbiome variation between animals and humans and across human populations.

The committee considered research showing that the human microbiome varies across populations due to differences in genetics and environmental factors, such as diet. Better knowledge of this variation could improve assessments of individual susceptibility to the effects of environmental chemicals, they said.

Similarly, the human microbiome differs from those of species used in toxicology studies. The experts advised that a better understanding of microbiome variation across species could help determine how the findings of animal studies may be relevant to humans.

Barriers and opportunities

The report identified several barriers to implementing the proposed research strategy. For example, new methods are needed to identify specific microorganisms that metabolize environmental chemicals and the enzymes they use to do so. To overcome these barriers, scientists will need substantial resources, better experimental standardization, and interdisciplinary collaborations.

“This report provides invaluable guidance for research agencies such as the NIEHS and EPA, to help them plan and prioritize future research in this area,” Chadwick said. “Incorporating the microbiome into the risk assessment framework will provide a more comprehensive picture of the risks associated with exposure to environmental chemicals.”

Citation: National Academies of Sciences, Engineering, and Medicine. 2017. Environmental Chemicals, the Human Microbiome, and Health Risk: A Research Strategy. Washington, DC: The National Academies Press.

(Janelle Weaver, Ph.D., is a contract writer for the NIEHS Office of Communications and Public Liaison.)