Microbiome

Introduction

The microbiome is the collection of all microbes, such as bacteria, fungi, viruses, and their genes, that naturally live on our bodies and inside us. Although microbes require a microscope to see them, they contribute to human health and wellness in many ways. They protect us against pathogens, help our immune system develop, and enable us to digest food to produce energy. Some microbes alter environmental chemicals in ways that make them more toxic, while others act as a buffer and make environmental chemicals less toxic.

The critical role of the microbiome is not surprising when considering that there are as many microbes as there are human cells in the body.¹ The human microbiome is diverse and each body site – for example, the gut, skin, and oral and nasal cavities – is home to a unique community of microbes.² A person’s core microbiome is formed in the first few years of life, but can change over time in response to different factors including diet, medications, and a variety of environmental exposures.

Differences in the microbiome may lead to different health effects from environmental exposures and may also help determine individual susceptibility to certain illnesses. Environmental exposures can also disrupt a person’s microbiome in ways that could increase the likelihood of developing conditions such as diabetes, obesity, cardiovascular diseases, allergies, and inflammatory bowel disease.³

What is NIEHS Doing?

NIEHS studies the microbiome to gain a better understanding of its complex relationships with the environment, and how these interactions may contribute to human health and disease. This knowledge could help us revolutionize the way new chemicals are tested for toxicity, and design prevention and treatment strategies for diseases that have environmental causes.

NIEHS-supported research related to the microbiome includes the environmental factors described below.

Chronic stress – NIEHS researchers found chronic stress disturbs the gut microbiome in mice, triggering an immune response and promoting the development of colitis, a chronic digestive disease characterized by inflammation of the inner lining of the colon.⁴

Artificial sweeteners – A NIEHS–funded study found sucralose, a widely–used artificial sweetener, changes the gut microbiome in mice and may increase the risk of developing chronic inflammation.⁵ In a separate study, they found that acesulfame–potassium, another artificial sweetener, induced weight gain in male, but not female, mice.⁶

Diet – NIEHS researchers showed a high–fat diet shaped the gut microbiome of mice in a way that predisposed them to gain weight and develop obesity.⁷

Caesarean delivery – NIEHS–funded research indicates the way a newborn enters the world, by C-section or natural birth, and what is eaten, formula or breast milk, during the first six weeks of life may affect the type of microbes in the gut microbiome.⁸

Antimicrobials – A NIEHS–funded study examined the effects of triclosan, a common ingredient in antimicrobial products, on the gut microbiome in mice. Mice that consumed triclosan through drinking water displayed an uptick in bacterial genes related to the stress response, antibiotic resistance, and heavy metal resistance.⁹

Arsenic – NIEHS–funded researchers showed arsenic exposure in mice changed the gut microbiome and altered molecular pathways in bacteria that are important to biological functions like DNA repair.¹⁰

Pathogens – A NIEHS–funded study showed pathogens, microbes that cause infection or disease, in oral mouthwash samples were associated with pancreatic cancer in humans.¹¹

Pesticides – A NIEHS–funded study reported exposure to the widely used agricultural insecticide diazinon changed the gut microbiome of mice.¹²  These changes were more pronounced in male than female mice, providing insight into previously reported sex–specific effects of this toxicant on the nervous system.

Ultrafine particles – NIEHS–funded research found breathing ultrafine particles, a component of air pollution, altered the gut microbiome and changed lipid metabolism in mice with atherosclerosis.¹³

Further Reading

Stories from the Environmental Factor (NIEHS Newsletter)

• NIH Researchers Tackle Questions on Air Pollution and Pregnancy (September 2019)
• Infectious Disease and the Environment — a Two-way Street (February 2019)
• Role of the Microbiome in Exposure Risk — a Call for Research (February 2018)
• Distinguished Lecture Focuses on Importance of Microbiome (February 2017)
• Microbiome and Environmental Health Highlighted at Workshop (February 2016)

Podcasts

• Arsenic in Rice and Other Foods
• Obesity and the Environment
• The Exposome
• The Microbiome

Additional Resources

• Environment and Health: What’s the Human Microbiome Have to Do with It?
  The National Academies of Sciences’ Standing Committee on Use of Emerging Science for Environmental Health Decisions held a two-day workshop in 2016. Presentations from this event are available in video and PDF formats.
• Human Microbiome Project (NIH) – This website contains archived information about research sponsored by the Common Fund from 2007 to 2016
• Microbes, the Environment, and You (NIEHS) – Read about the speakers and their presentations from this 2014 webinar by the NIEHS Partnerships for Environmental Public Health.
• Teaching the Microbiome (NHGRI) – This web page contains a list of resources for educators.