Changes in diet and physical-activity patterns associated with agriculture, in conjunction with increased population densities and exposure to zoonoses, resulted in what is known as an epidemiological transition, a shift in the causes of morbidity and mortality among humankind (Omran 1971). The first epidemiological transition from foraging to food production resulted in increases in dental caries, nutritional deficiencies, infectious disease, and skeletal conditions like osteoarthritis, as well as decreases in growth and height (Larsen 2014). A second epidemiological transition occurred following the Industrial Revolution in Western Europe and the United States when socioeconomic, political, and cultural conditions contributed to improved standards of living, hygiene, and nutrition that minimized the effects of infectious disease, after which people began to experience the that are the focus of the remainder of this chapter (Omran 2005). With the addition of immunizations and other public health initiatives, modified forms of this transition remain ongoing in many low- and middle-income countries (Zuckerman et al. 2014), with several now facing a “double burden” of disease, with poor, often rural, populations falling prey to infectious diseases, while more affluent citizens are victims of chronic illnesses. A third epidemiological transition is now underway as infectious diseases, some of them novel, others re-emergent, and others even multi-drug resistant, have once again become major health concerns (Harper and Armelagos 2010; Zuckerman et al. 2014). These include Ebola, HIV/AIDS, tuberculosis, malaria, dengue, Lyme disease, and West Nile virus, all zoonoses that initially spread to humans through contact with animals. These diseases are increasing their geographic ranges due to climate change, economic development, and deforestation (Baer and Singer 2009).
Patterns of morbidity and mortality continue to shift across the globe. As with the first epidemiological transition resulting from the adoption of large-scale agriculture, such shifts can be the direct, if unintended, result of human interactions with the environment. For example, there has been a well-documented rise in chronic inflammatory diseases (CIDs) in recent decades in developed countries (Versini et al. 2015). This includes increased rates of allergic conditions like asthma, as well as autoimmune diseases like rheumatoid arthritis, multiple sclerosis, Crohn’s disease, and inflammatory bowel disease. This has coincided with the decrease in infectious disease associated with the second epidemiological transition, and the two are related. The “hygiene hypothesis” postulates the rise in CIDs is a result of limited exposure to nonlethal environmental pathogens in utero and early childhood (Zuckerman and Armelagos 2014). Modern human societies have become so sanitized that we are no longer exposed to microorganisms that stimulate the development of a healthy immune system (Versini et al. 2015). “In effect, the lifestyle changes—sanitary improvements, pasteurization, use of antibiotics, and improved hygiene—that contributed to the second transition may have produced a substantial trade-off in health and quality of life, with developed nations exchanging a high burden of infectious disease for a higher burden of CIDs” (Zuckerman et al. 2014).
Similarly, the re-emergence of infectious disease, the third epidemiological transition, reflects the continuing relationship between humans, animals, and pathogens. Over 60% of between 1940 and 2004 have been of zoonotic origin, with over 70% stemming from human contact with wildlife (Jones et al. 2008). The global bushmeat trade currently devastating Africa’s wildlife is a continuing source of Ebola infection (Asher 2017), as well as the original source of HIV and viruses related to leukemia and lymphoma among humans (Zuckerman et al. 2014). Further, new strains of avian (bird) flu, some with mortality rates as high as 60% among human victims (WHO n.d.), are transmitted to humans through poultry production and contact with wild birds; these pose a looming global threat of epidemic disease (Davis 2005). Lastly, the use of antibiotics in commercial meat production is directly related to the rise of drug-resistant strains of previously controlled infectious diseases. An estimated 80% of antibiotics in the U.S. are used to promote growth and prevent infection in livestock, and drug-resistant bacteria from these animals are transmitted to humans through meat consumption (Ventola 2015).
These examples illustrate continuing interaction between humans, our evolved biology, and the physical and cultural environments in which we live. The remainder of this chapter will focus on selected noncommunicable diseases and the social, cultural, and environmental factors that contribute to their prevalence in modern, industrialized economies. We begin with the health condition that affects all of the others—obesity.
