U.S. flag

An official website of the United States government

NCBI Bookshelf. A service of the National Library of Medicine, National Institutes of Health.

Institute of Medicine (US). Rebuilding the Unity of Health and the Environment: A New Vision of Environmental Health for the 21st Century. Washington (DC): National Academies Press (US); 2001.

Cover of Rebuilding the Unity of Health and the Environment

Rebuilding the Unity of Health and the Environment: A New Vision of Environmental Health for the 21st Century.

Show details

3Human Health and the Natural Environment

Fifty years ago, the World Health Organization (WHO) defined health as “a state of complete physical, mental and social well-being and not merely the absence of disease or infirmity.” This definition should serve as a reminder that redefining the view of environmental health and the natural environment requires many shifts in thinking, as well as a willingness to pursue a diversity of approaches.

Advances in the field of environmental health have taught us much about human health hazards; for example, air pollution can cause respiratory disease, heavy metals can cause neurotoxicity, global climate change is likely to fuel the spread of infectious diseases. Domestically, the response has been to clean up the environment, a laudable goal, said Rafe Pomerance of Sky Trust. Environmental health issues traditionally have been addressed at the international level within the context of such issues as ozone depletion, climate change, and biodiversity. Countries have tried to address these issues through the multilateral process, such as multilateral agreements and commissions, bilateral assistance and cooperation, private sector investment, trade, the work of nongovernmental organizations, education, and training.

These efforts can be profoundly effective, asserted Pomerance; witness the reductions in the emissions of chlorofluorocarbons achieved through legislation and transnational agreements in the 1970s. Industry, especially newer companies with the capacity to design “greener” manufacturing practices, has made some inroads into environmentally friendly production. However, efforts have not been so successful in maintaining biodiversity, said Pomerance, as the world continues to lose species on a daily basis. Challenges also remain in assuring a safe and healthful food supply.

The natural environment, broadly conceived, can also enhance health, for example, many pharmaceuticals are derived from plants and animals, providing a compelling argument for preserving biodiversity. In addition, contact with the natural world may be directly beneficial to health. If so, then the field of environmental health needs to extend beyond mere considerations of toxicity. According to the speakers, research and policy must be directed toward understanding the interactions of human health and the natural environment, from the most personal level—that is, how individuals interact with the world around them—to the global scale—that is, how nations agree to reduce pollution, pursue sound agricultural and land use practices, and feed their citizens. Each of these issues is explored below.


A theoretical basis for the notion that contact with nature is beneficial comes from E.O. Wilson, who introduced the term Biophilia almost 20 years ago, defined as the innately emotional affiliation of human beings to other living organisms. From an evolutionary perspective, a deep-seated connection with the natural world should be no surprise. Humans have been evolving for more than 2 million years, yet have lived relatively insulated from nature for only the last 10,000 years. As Wilson (1993) noted, “it would be quite extraordinary to find that all learning rules related to the natural world have been erased in a few thousand years, even in the tiny minority of peoples who have existed for more than one or two generations in wholly urban environments.”

This is not a new idea, claimed Howard Frumkin of Emory University. The human connection to nature and the idea that this might be a component of good health have a long and fascinating history in philosophy, art, and popular culture. There is ample evidence—from animals, plants, landscapes, and wilderness experiences—that we can build on this affiliation to enhance our health.

Animals have always played a prominent part in human life. Today, more people go to zoos each year than to all professional sporting events. More than half of all U.S. households own pets. Animals comprise more than 90 percent of the characters used in language acquisition and counting in children’s preschool books. A considerable body of evidence links contact with animals to human health. According to Frumkin, preserving the bond between people and their animals, like encouraging good nutrition and exercise, appears to be in the best interests of those concerned with public health.

Exposure to plants and flowers also nourishes a sense of our well-being. In a 1998 National Gardening Survey of more than 2,000 randomly selected households, half of the respondents agreed with the statement that flowers and plants at theme parks, historic sites, golf courses, and restaurants are important to enjoyment of these locations, and 40 percent agreed with the statement that being around plants makes them feel calmer and more relaxed. Office employees report similar feelings, stating that an office with plants is a more desirable place to work. Psychologist Michael Perlman has written of the psychological power of trees, as evidenced by mythology, dreams, and self-reported emotional responses. Indeed, the concept that plants have a role in mental health is fairly well established, said Frumkin. Of note, hospitals have traditionally had gardens as an adjunct to recuperation and healing. Perhaps this time-honored practice reflects a recognition that proximity to plants, like proximity to animals, may in some circumstances enhance health (see Figure 3.1).

FIGURE 3-1. The addition of gardens has been shown to be essential for mental health and helps individuals recuperate after illness.


The addition of gardens has been shown to be essential for mental health and helps individuals recuperate after illness. SOURCE: H. Frumkin. Reprinted with permission.

To return to an evolutionary perspective, human history probably began on the African savanna, a region of open grasslands punctuated by scattered stands of trees and denser woods near rivers and lakes. When offered a choice of landscapes, people react most positively to savanna-like settings, with moderate to high depth or openness, relatively smooth or uniform-length grassy vegetation or ground surfaces, scattered trees or small groupings of trees, and water, a finding that is consistent across every culture studied.

This effect may extend beyond aesthetics, to restoration of health or recovery from stress. Research on recreational activities has shown that people viewing savanna-like settings report feelings of tranquility, peacefulness, or relaxation. On psychometric testing, people viewing such settings show decreased fear and anger, enhanced positive affect, and improved mental alertness, attention, and cognitive performance.

The same results emerge from studies that directly consider conventional health end points. In 1981, University of Michigan architect Ernest Moore found that “prisoners assigned at random to cells along the prison’s outside wall with a view of rolling landscape and trees, had significantly lower frequency of sick call visits compared to those in the inside cells.” Moore could not identify any design features to explain this difference and that the outside view may provide some stress reduction (Moore, 1981).

Similar observations come from health care settings. A 1984 paper in Science bore the provocative title View Through a Window May Influence Recovery from Surgery. “Postoperative patients, assigned essentially randomly to rooms with views of trees, had statistically significantly shorter hospitalizations, less need for pain medications postoperatively, and fewer negative comments in the nurses’ notes, compared to patients with the brick views” (Ulrich, 1984).

Physician David Cumes has described “wilderness rapture,” including self-awareness; feelings of awe, wonder, and humility; a sense of comfort in and connection to nature; increased appreciation of others; and a feeling of renewal and vigor (Cumes, 1998). These outcomes are often cited in favorable accounts of so-called wilderness therapy for a variety of psychiatric, organic, and emotional disorders. Most published studies relate to mental health end points, and although they are limited, many do suggest some benefit from wilderness experiences. Mental health has been studied more than somatic conditions, and short-term benefit has been demonstrated more than long-term benefit.

The value of wilderness is not lost on the American public, said David Hayes, U.S. Department of the Interior. The Interior Department owns about half a million acres—more than 20 percent of the land mass of the United States—through the National Park Service and the National Wildlife Refuge System. Americans rely on these for open space and recreational opportunities. According to Hayes, the Interior Department manages more than 300 million visits a year, reflecting a deeply rooted interest in our physical environment.


There is a powerful connection between the variety of life on earth and our own well-being, for example, the contributions of natural products to the pharmacopoeia, research, and diagnostic tools, and as indicators of pollution-related disease.

In the pharmacopoeia, the natural world is continuously offering compounds that are useful in medicine, and the search for biologically active compounds continues. Tom Lovejoy of the World Bank provided examples of this, including compounds obtained from slime molds from the banks of the Zambezi River that are effective in the treatment of tumors resistant to taxol; the immunosuppressant cyclosporin, which comes from a fungus; analgesics from tropical sea organisms and poison frogs; and lovastatin, which comes from the bacterial world.

Biodiversity is essential for guaranteeing the healthiness of humans.

—Tom Lovejoy

Natural products are often essential in both research and diagnostic tools, said Lovejoy, the prime example being the polymerase chain reaction, which relies on a naturally occurring substance to initiate the reaction. Another example involves horseshoe crabs, the blood of which is useful in detecting certain impurities in drugs. Other species can also provide unexpected insight into our own biology; for example, a pit viper from South America has a venom that causes its victims’ blood pressure to drop to zero permanently. Brazilian scientists studying this snake 20 to 30 years ago uncovered the angiotensin system of blood pressure regulation. This research eventually led to the development of a class of drugs known as ACE (angiotensin-converting enzyme) inhibitors.

Biological diversity also serves as a set of indicators of environmental change, for example, the study of endocrine-disrupting chemicals in wild species and the decline and disappearance of the world’s amphibian species. Biological diversity becomes the ultimate integrator of all the things affecting living systems, said Lovejoy. An additional way in which biodiversity connects with human health is in reducing environmentally caused disease. There is an active field using biological systems, principally microbes, to clean up toxic waste problems in the environment, particularly PCBs, oil spills, and heavy metals. Biological systems increasingly are being seen as potential means of cleaning up the water supply through the restoration of watersheds.


Agriculture directly affects human health in two major ways: (1) through the environmental and ecosystem changes of farm production and (2) through an available and nutritious supply of food. According to Richard Rominger, deputy secretary of the U.S. Department of Agriculture (USDA), USDA nutrition programs help feed one in six Americans each month. Federal agricultural initiatives also aim to develop new technologies to protect the environment by shifting to lower-risk pesticides or pesticide alternatives and by conducting research on greenhouse gas and carbon storage that will affect global climate change. At the local level, USDA provides technical assistance to help private landowners with conservation practices in order to promote sustainable development. Sustainability recognizes that farmers can be productive and profitable and still be wise stewards of their lands and the environment.

Sustainability recognizes that farmers can be productive and profitable while being wise stewards of their land and the environment.

—Richard Rominger

The provisions of the 1996 Farm Bill aim to achieve environmental benefits that include soil, air, water, and wildlife habitat conservation, as well targeted efforts to preserve the health of rivers and streams. In early 2000, President Clinton proposed a conservation security program to further strengthen the economic–environmental linkage. By providing direct stewardship payments to farmers with comprehensive conservation plans, the program highlights the voluntary and locally led aspect of private land conservation efforts. This is far bigger than just a farm issue. Society benefits from a healthy environment and the plentiful food that it produces.

One key provision of the program boosts funds to help producers with nutrient management. For example, improperly managed animal feeding operations can contribute to water pollution, outbreaks such as Pfiesteria in the Chesapeake watershed, or excessive runoff from dairy operations.

For agriculture, greenhouse gas emissions present some challenges and perhaps some opportunities. The U.S. Global Change Research Program has reported that the production of major crops could very likely increase with global warming, but there might also be a 20 percent increase in the use of pesticides, with an environmental impact that could be substantial. Current research is centering on agriculture’s capability as a huge sink to absorb and store carbon. By sequestering carbon in agricultural soils, we could achieve more than just pulling carbon dioxide out of the atmosphere and cutting the rate of global warming, said Rominger. Increasing the soil’s organic content would improve its water-holding capacity, fertility, and productivity.

While considering the impact of agricultural systems on global climate change, we must also narrow the focus to the connection between microbiological pathogens and food safety. It is estimated that 5,000 people die and 76 million get sick each year from foodborne illnesses. In the past 7 years, said Rominger, the nation’s science-based inspection system has resulted in a sharp drop in the prevalence of salmonella in raw meat and poultry. Science and technology are the first line of defense against future food safety challenges, for example, via Foodnet and Pulsenet. However, certain pathogens and other microbes are evolving resistance on a global scale to traditional control methods, including antibiotics.

While food safety is a key aspect of a food-secure world, it is just part of the definition. There can be no security if food is not available and abundant and if nutritional needs are not met. “Our farmers can grow the most abundant and nutritious produce in the world,” said Rominger, “but if Americans do not heed the advice of newly released dietary guidelines, their diets will still get a failing grade.” This is more a matter of education than farm and agricultural policy. It is as central to the total environmental health connection as conservation measures on the farm and pathogens under the microscope.


Common sense tells us that a sound environment is important to human health. However, only in recent years have science and technology provided us with ways to measure the correlation between a healthy environment and a healthy body. The natural environment in which we spend our days and the national and international community in which environmental protections must be negotiated provide both a local and a global perspective by which to consider environmental health.

Although there clearly is an interdependence between public health and the environment, workshop participants noted that we have limited resources for identifying and understanding challenges to health or implementing intervention strategies. Some of the higher-order issues, such as sustainability, must be addressed if we are to achieve better health, noted Rafe Pomerance. Another central quandary is the reduction and disposition of waste. We cannot continue to have consumption that outweighs the production capacity of our ecosystems, and we cannot continue to produce waste at a rate that outweighs our ability to assimilate it back into the ecosystems without negative impacts, said William McDonough.

A second challenge is to develop baseline data on different environmental stressors. Impacts of a poor environment on public health can be direct or indirect. Speakers noted that we have tended historically to focus on the direct effects of pollution on public health—for example, toxicity or adverse health effects—and less on the bioindicators that can measure direct and indirect effects through impacts on ecological systems.

To meet these challenges, several workshop participants stated that we need to develop more holistic and integrated approaches to environmental health that incorporate considerations of human biological and ecological health and achieve better understanding of these interrelationships. The systems view of the ecologist must be adopted as a new paradigm for the environmental health scientist.

Copyright © 2001, National Academy of Sciences.
Bookshelf ID: NBK99584


  • PubReader
  • Print View
  • Cite this Page
  • PDF version of this title (1.8M)

Recent Activity

Your browsing activity is empty.

Activity recording is turned off.

Turn recording back on

See more...