Did You Know That Soil Health Affects Human Health?

June 13, 2023 | 9:32 am
photo of green sprouts coming up from dark, rich soil, with sunlight shining down from aboveSabina Gahramanova/Shutterstock
Omanjana Goswami
Interdisciplinary Scientist

As a part of the Consolidated Appropriations Package passed in 2022, Congress directed the National Academies of Sciences, Engineering, and Medicine (NASEM) to investigate the links between human health and soil health, looking into how soil management practices that support healthy soils influence the nutritional content of foods and affect overall human health.

In response, NASEM convened a panel of multi-disciplinary academic experts who can bring the most relevant and current scientific knowledge to the table. The committee’s final report is expected to identify knowledge gaps and future directions for promising research, and offer recommendations for improving the human health benefits of what these experts call the soil microbiome.

The Union of Concerned Scientists (UCS) teamed up with our partners at the National Sustainable Agriculture Coalition and Representative Chellie Pingree’s office to weigh in on the scope of the study, highlighting the need to examine the impact of different agricultural production systems.

But before we get to our recommendations, let us take a short detour to understand what the soil and human microbiomes are, and how they are linked.

The vital relationship between soil, farming, and our food

You might have heard of the human microbiome: it is the basis of a healthy gut and is made up of billions (or maybe trillions) of interconnected microbial cells in our gut—cells that control numerous essential functions like digesting our food, regulating our immune system, and protecting us against disease (to name a few).

Much like the human microbiome, the soil (or dirt as it’s known colloquially) is home to numerous types of microscopic organisms collectively known as the soil microbiome. This microbiome is responsible for maintaining plant life on Earth, essentially controlling ecosystem services and functions like nutrient recycling, protecting the soil structure, and protecting plants from pathogens.

Research has shown that the soil and human microbiomes are interconnected. Human activities can alter the distribution and abundance of soil microorganisms, especially by changing how food is grown: for example, by changing the quantities of synthetic fertilizers and pesticides used, or by growing the same crops on the same fields year after year. And these changes to the soil microbiome result in changes to the human microbiome. While we have plenty of scientific evidence of this relationship, there isn’t a single comprehensive explanation of how it all plays out because of the complex nature of myriad interconnected interactions within the human body.

One long-term, field-scale scientific study showed the microbial community in organically farmed soils was much more diverse than conventionally managed soils (i.e., treated with chemical fertilizers), and was full of microbes that protect plants against pathogens. Organic farming was also shown to support enhanced levels of soil organic carbon, soil nitrogen, and microbial biomass, and to improve soil structure—all of which are markers of healthy and resilient soils.

Farming methods can also affect the nutrition density of crops—that is, the vitamins and nutrients in our food—and hence impact the human microbiome. The Rodale Institute’s Farming Systems Trial is a well-known long-term field study on the effects of farming practices on the nutritional quality of food. Since 1981, scientists at the Institute have grown the same crops in adjacent plots to compare the effects of organic and conventional practices. Results published in a 2018 study showed that soil organic matter and nitrogen levels had significantly increased on the organic plots, but not on the plots following conventional agriculture.

Soil biodiversity, especially diverse microbial communities in the soil, provide a range of benefits to human health, such as suppressing pathogens, enhancing crop nutrient uptake, and improving the overall nutritional value of food. In the Rodale study, for example, vegetables grown under the two systems showed large differences in total antioxidant and vitamin C levels. Organically grown tomatoes and jalapeno peppers contained 36 percent and 18 percent more vitamin C, respectively, than the conventionally grown vegetables. Organic carrots had 29 percent higher total antioxidant levels. In a nutshell, healthier soils with more soil biodiversity are better at producing more nutrient-dense crops.

The scientific literature is full of evidence that the soil microbiome has several direct and indirect effects on human and public health. These effects arise from the complex interactions of soil health, food production systems, food access, and individual and community well-being.

We need to know more about the role agricultural production systems play

UCS commends NASEM for convening its panel of experts and addressing the congressional directive to explore the linkages between the soil and human microbiomes. In a letter to NASEM, we advocated for the experts to adopt a systems perspective as opposed to taking a narrower, siloed approach. In particular, we asked the committee to consider: 

  • How different production systems (e.g., organic, conventional, animal) impact microbiomes and the overall health of both the soil and the people who work in these systems—farmers and farmworkers
  • The potential for different soil health practices to remediate contamination from environmental toxins such as per-and polyfluoroalkyl substances (PFAS), or so-called forever chemicals
  • Linkages between production systems, soil health, and the nutritional density of foods
  • Effects of production systems on community vitality, addressing environmental and human health (including mental health)
  • The potential for improved production systems to benefit soil health, help address climate change, and increase the availability and accessibility of culturally preferred and healthy foods

As the committee begins its work, it is important to remember that this year Congress is negotiating the next food and farm bill, and that means we have an opportunity to transform our food and farming systems. One bill in particular, the Agriculture Resilience Act, focuses on improving soil health and delivering climate benefits. I encourage you to reach out to your member of Congress and ask them to pass a food and farm bill that’s a win for both people and the environment.