In current medical practice, health is understood as the absence of disease. In keeping with this understanding, contemporary medicine is focused on the treatment and management of disease. It is engaged in tracing etiologies, identifying symptoms, classifying conditions, and studying pathology. This approach has led to the development of increasingly complex, sophisticated, and costly treatments for treating disease, by preventing pain, slowing disease progression, and decreasing disease-associated disability and mortality. In all these activities, there is a strong emphasis on effecting or finding a cure and restoring health, whatever that might be.
This disease-focused approach of modern medicine stems in part from its legacy acquired from fighting infections. Infectious diseases have an identifiable cause, a pathogen, which when eliminated, restores the individual to health. If right drugs and treatments are available, then therapy is straightforward. Its primary objective is to remove microbes and to minimize their pathogenic effects. While this model works for infectious diseases, non-communicable diseases are different. In non-infectious diseases, there is no single, offending pathogen. The disease is usually localized to the tissue, and therefore could not be readily removed from its site to restore health. The pathology is native to an individual and not a foreign invasion, and therefore, the disease cannot be readily exorcised from the afflicted.
Moreover, current non-communicable diseases such as cancer, diabetes, and heart disease, cannot (yet) be cured, but simply managed. Health in the context of non-communicable disease is not simply a state that exists when a pathogen is absent – but a predisposition that may or may not progress to disease. The obvious question to ask then is whether health is a graded entity that could be measurable or promoted? But this is not an easy question to answer. Old models of health and disease are not entirely applicable, but no new paradigms have emerged. In the meanwhile, the global burden of non-communicable disease continues to grow, even in countries like the United States and Europe, where a dazzling array of medical treatments and procedures are widely available. It is evident that we have to develop a new understanding of health, not only to passively prevent disease, but to actively promote health. But, to promote health, which is not merely the absence of disease, we need first to redefine health and then to realize it – not only as an accepted concept, but an actionable goal
To expand the definition of health, understood as the absence of disease, the World Health Organization in the Preamble to its constitution in 1946, defined health “as a state of complete physical, mental, and social well-being, and not merely the absence of disease or infirmity.” This definition, while extending the concept of health beyond disease, could be faulted for it descriptive ambiguity and a lack of clarity. No one can define or quantify “complete” physical, mental and social well-being, the quality of completeness is not only unattainable (or only temporarily achievable), but it may also be different for different people. The ambiguity is further compounded by the concept of well-being, which is subjective and non-quantifiable, and as a result, non-actionable. Clearly, we need a new definition.
The deficiencies of the WHO definition have been widely recognized. To address such criticism, the WHO redefined health as “the extent to which an individual or a group is able to realize aspirations and satisfy needs and to change or cope with the environment.” The definition succeeds in emphasizing health as a means, not an end. It also correctly views health as a resource – an ability to maintain homeostasis, and to withstand stress and recover from insults. In this concept, a person who can handle stress, maintain productive social relationships, and achieve self-prescribed goals is considered healthy. While this view accommodates the possibility that health could be improved or strengthened, it does not explain how health could be assessed or measured. More importantly, it localizes health to the individual, seen as a discrete entity, the ultimate unit of interest. Within this individualized context, health is viewed as an ability or quality that is the characteristic of a specific person, a discrete and siloed from other members of the society, and separate and distinct from the surrounding natural environment.
This localization of health to an individual overlooks that fact that humans exist, not as discrete independent entities, but as nodes within social networks. These large and complex social networks have their own identity, fashioned from their unique history and culture. Moreover, these networks are embedded in specific ecosystems to which they have variably adapted during the course of their evolution. Therefore, human health, like human identity, cannot be understood as an entity separate from the identity and the health of the ecological and social networks of which each individual belong. Even if we were to see health as an individual ability, we have to understand that this ability is not entirely localized to a person and not determined entirely by a specific person’s biology or volition. The resilience of an individual to disease is derived, at least in part, from a larger pool of social and natural resources, and is defined by elements that belong to the larger environmental context, often outside an individual’s reach or control.
One way to formulate an inclusive concept of an individual within a specific environment, is to adopt the omics approach developed by geneticists, and psychologists. Using this approach, we could construct a collective model of different environmental factors as an envirome to reflect the totality of environmental conditions that affect an individual. The envirome could be understood as the sum of all external conditions that effectuate and regulate the translation of the genome to the phenome, throughout the lifespan of an individual. It comprises interdependent sets of natural, social and personal conditions that collectively permit the expression of genome and thereby regulate human development, health and disease susceptibility. Envirome is what the genome need to actualize itself. And we become us as a result of the interactions between our genome and our envirome.
Although features of individual enviromes may be shared by many individuals that live within a specific set of social conditions or ecological niches, the envirome, like the genome is unique to a specific individual. This specificity of the envirome, distinguishes it from current models of the social determinants of health, which often do not account for the personal microenvironments, created and populated by lifestyle choices and living conditions specific to a person. These microenvironments distinguishes an individual’s experience from other members living within similar geographic and social conditions and it allows for understanding how social influences are filtered, selected, and rectified by the personal domains of an individual and the specific choices made by a person. Moreover, the social determinants of health, considered in isolation, often do not account for the effects of the natural environment or how geographic features affect the evolution of societal structures and the health of specific individuals within that specific society. Because the social, personal, and natural domains of the envirome are so inextricably intertwined, they cannot be readily unwoven without losing the pattern intrinsic to this weave. It is, therefore, important to understand the natural, social, and personal determinants of the health within the same framework so that comprehensive diagnosis and remediative solution could be targeted to this pattern, and not just to the most accessible strand of influence.
The envirome model offers a fresh perspective of both human health and disease. In this view, health could be considered as a state of equilibrium between the envirome and the genome and disease as a mismatch between the two. During the life course of an individual, external challenges from the envirome could be mitigated if there is genomic capacity to withstand and counter such insults. For instance, detrimental outcomes of bacterial or viral infections could be avoided, if an individual has innate immunity against such pathogens. Likewise the effect of toxic exposures could be alleviated, if there are genetic resources to counter such insults. In addition to such intrinsic capacity, health is also due to genomic concordance with the natural and social domains of the environment. For instance, Tibetans living in the Tibetan plateau are healthy, despite the high altitude, because they have developed genomic resilience to live in such harsh condition. Such resilience or health may also be due to living in favorable enviromic conditions – for example individuals living in areas with high access to walkable areas are likely to be less susceptible to obesity and those living near the equator may be more resistant to hypertension (because of greater exposure to UV radiation from the sun).
Consideration of the envirome also compels us to examine health as a more inclusive concept than currently understood. If we consider a person to be a part of a complex envirome, then health relates not only to the ability of a discrete, truncated individual, but also the resilience or the health of his or her envirome. For the natural domain of the envirome, this would include the health of the natural environment as it relates to greenness, biodiversity, climatic conditions and pollution – factor that have been found to exert an importance influence on human health, disease susceptibility and longevity. In the social domain, health would relate to cultural and economic health of the society, as well as the intellectual, psychological, spiritual, and nutritional resources that these societal factors provide. And, importantly, how natural and social resources are used to continuously assemble and disassemble the personal domains of the envirome. It is significant that all these forms of health, are in principle quantifiable, even though in many instances, validated measures of these forms of health are missing, but need to be developed.
Returning to the important premise that health results when the genomics and enviromics are confluent, the broader description of the envirome brings the state or health of the natural, social and personal environments as essential and largely untapped. While the frontiers of genomics develop gene editing technologies to improve health, our understanding of what constitutes a healthy envirome has no such interventional mindset. Could adopting the enviromic view change current views of health and disease? Yes. If we view an individual as a part of his or her envirome, health could be enhanced as effectively by targeting the different domains of the envirome as by targeting the individual per se. By accepting that the health of the natural environment is inextricably linked to the health of the individual, we can enhance human health by decreasing pollution, planting trees, and promoting biodiversity. We can also prevent disease by building healthier urban and rural environments, cities that are conducive of walking and invite physical activity, support social networks that promote social cohesion, and minimize social and personal conditions that promote aggression, violence, addiction, discrimination, and economic disparities. We can encourage the construction of personal environments that empower, and lifestyles that favor healthier choices in nutrition, learning, education and physical activity. Even when preventive efforts are targeted to the individual, we can see that much could be gained by understanding that lifestyle choices of individuals are, to a large extent, shaped by social and natural domains of the environment. For examples, lifestyle choices such as those related to nutrition, physical activity, chemical use, and addiction are constrained or abetted by social conditions, such as advertising as well as the availability of drugs, cigarettes, and alcohol in specific neighborhoods. Importantly, individual lifestyle choices are also shaped, in large measure, by social norms and prevailing culture.
Partial attribution of lifestyle choices to the social environment does not minimize personal responsibility. But it does delineate, the extent to which both – individual choice and social acceptance contribute to these choices. Once the contribution of both individual and social factors is clearly delineated, we can readily target their confluent effects and thereby maximize prevention by not targeting individuals when social influences are strong or trying to effect social change when a change in the behavior of a few individuals would suffice. For instance, rates of smoking could be decreased not only by educating individuals about the dangers of smoking, but also increasing taxes on tobacco, decreasing cigarette advertising, prohibiting sales to minors, banning public smoking, and de-normalizing smoking behavior so that it is not a socially accepted practice. Similar approaches targeting both the social and personal domains of the envirome could be adopted to promote other health behaviors such as those relating to nutrition, drug use, and physical activity. Even then, some social factors are likely to be beyond the control of the individual. For instance, air pollution, food contamination, exposure to toxic chemicals. These can be addressed only at a societal level and therefore concerted social action is needed to minimize their adverse health effects.
By viewing health as a modifiable ability, we can alter medical practice, by looking at causes of diseases beyond the individual to the interaction of the individual with his or her envirome. For instance, much of the risk of diabetes and heart disease could be diminished by regulating sleep or synchronizing the circadian rhythm of an individual with the diurnal cycle of night and day. The outcomes of stroke and heart failure could be improved by decreasing exposure to air pollution. And the need for pain medication after surgery could be reduced simply by housing patients in rooms with a view of green scenery. Of course for all of this to happen, we need to develop a much wider evidence base as well as quantitative measures of health understood within the context of the envirome. A more robust evidence base to support this model would require extensive new research into the relationship between different domains of the environment and individual health. More work will also be required to determine how well individual genomes match with the individual enviromes and whether there are discordant factors in the personal, social or natural environments that could be altered to minimize this mismatch. But before we can do that, we will have to develop validated scales that measure health in all its forms. Even if we succeed in redeeming, in small measure, the promise of this approach, we will impact, more significantly, the growing burden of disease in contemporary societies and enhance, more effectively, the health of human populations and their environments.