Environmental Influences on the Human Microbiome and Implications for Noncommunicable Disease

Abstract

The human microbiome contributes metabolic functions, protects against pathogens, educates the immune system, and through these basic functions, directly or indirectly, affects most of our physiologic functions. Here, we consider the human microbiome and its relationship to several major noncommunicable human conditions, including orodigestive tract cancers, neurologic diseases, diabetes, and obesity. We also highlight the scope of contextual macroenvironmental factors (toxicological and chemical environment, built environment, and socioeconomic environment) and individual microenvironmental factors (smoking, alcohol, and diet) that may push the microbiota toward less healthy or more healthy conditions, influencing the development of these diseases. Last, we highlight current uncertainties and challenges in the study of environmental influences on the human microbiome and implications for understanding noncommunicable disease, suggesting a research agenda to strengthen the scientific evidence base.

Keywords: human microbiome; interindividual variability; macroenvironment; microenvironment; noncommunicable diseases.

Figure 1

The effect of the environment on human health is a complex set of interactions between multiple exposures that, alone or more commonly interdependently, affect various structures and functions of the microbiome. This figure illustrates how environmental exposures have a direct impact on the human microbiome, implicated in human health and diseases, including orodigestive tract cancers, neurologic diseases, diabetes, and obesity. These environmental exposures are influenced by and interrelated with the macroenvironment, including the toxicological and chemical environment, built environment, and social environment, as well as the microenvironment, including smoking, alcohol, and dietary factors. Although external environmental impacts are illustrated, individual factors, such as age, sex, and genes, also interact with and eventually determine exposure, dose, and any subsequent response and effect.