Ecologic Models of Health
October 16, 2019
Key Points
- We start learning early in life about causal relationships.
- Simple cause-effect relationships may be easy to discern.
- Multiple causal agents that contribute to health or disease outcomes make up a causal system.
- Ecologic models emphasize multi-level inter-relationships and emphasize dynamic interactions among them.
- Feedback loops within systems can either work to maintain the system or to derail it.
- Relatively minor changes can have magnified effects downstream.
- Finding and managing key leverage points can turn whole systems around.
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by Nancy Hepp, MS, and BCCT advisor Ted Schettler, MD, MPH
Causes and Effects
Beginning early in childhood, we observe causes and effects: a smile brings forth other smiles. Touch a hot stove and burn your fingers. We infer relationships: single cause, immediate effect. Lesson learned—maybe.
The inquisitive child may later attempt to find out if a quick tap with her hand on the stove has the same effect. She is learning something about dose and duration of exposure.
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During a cholera epidemic in 1854, Dr. John Snow inferred a relationship between the Broad Street water pump in a suburb of London and the incidence of disease. He famously convinced officials to remove the handle from the pump, preventing people from using the contaminated water. The epidemic abated. It was not until 1883 that Robert Koch isolated the bacterium Vibrio cholera that we now know to be responsible for the infection.
This example also shows that an infectious agent by itself is not enough to cause disease. Vibrio cholera remained in the water supply, but people’s exposure to it was reduced. A viable infectious agent needs to be paired with human exposure and susceptibility to result in an outbreak of disease.
These relatively simple examples illustrate cause-effect relationships related to a single agent. Scientists, healthcare professionals and the general public commonly grapple with more complexity.
Complex Systems
Multiple causal agents that contribute to health or disease outcomes make up a causal system. The system is made up of multiple causal relationships, each of which is a link or a thread in a causal web. Each link is important, potentially able to influence how the system as a whole behaves. These more numerous causal links are commonly depicted in graphic ecologic models showing the inter-relationships among the parts.
Ecologic models typically emphasize multi-level inter-relationships and emphasize dynamic interactions among them. Ecologic models make clear the systems nature of many complex problems, whether it’s cancer in an individual, cancer patterns in communities and populations, or other diseases and disorders.
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Examples of ecologic models of health:
- One model looks at health and wellness from the level of the chemistry and processes of cell components up through cell functioning, organs, and a whole person. Uncorrected disturbances at any level can impact other levels. We discuss this in our Body Terrain and the Tumor Microenvironment page.
- Another model illustrates a nested hierarchy of person, family, community, ecosystem, society and planetary levels.
Hierarchy does not imply importance but rather indicates the multi-level nature of the model. Variables within each of these levels dynamically interact and can influence patterns of health and disease in individuals and entire populations.
Feedback Loops
Ecologic models try to account for dynamic feedback loops that act either to accelerate change or to dampen it.
Ecologic models try to account for dynamic feedback loops that act either to accelerate change or to dampen it. These loops are set into motion as system inputs and conditions change.
Some feedback loops help maintain system function, such as maintaining body temperature in a hot or cold environment, or a community response to natural disaster or disease outbreak. Other feedback loops derail the system profoundly, such illness that leads to unemployment, loss of home, poverty, and possibly further illness.
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Examples of feedback loops that can impact health:
Detrimental feedback loops:
- The physical design of housing and neighborhoods can either promote or discourage physical activity. This can affect sleep, stress, weight and fitness, making physical activity yet more difficult and ultimately affecting health.
- Neighborhood proximity to traffic or industrial activity can influence individual exposures to contaminants and noise. These exposures can impact children’s ability to attend school and their academic performance. Low academic performance can lead to fewer career options and lower pay or even unemployment, which will limit opportunities for healthy housing and neighborhoods across generations.
- Neighborhood poverty and lack of access to transportation and nutritious food often means that residents are left with the adverse health impacts of calorie-rich, nutrient-poor food. Poor health interferes with employment and education, tending to reinforce or worsen neighborhood conditions.
- Exposure to toxic chemicals can cause illness, disability and reduced cognitive abilities. Each of these can affect your ability to attend school, get a job, and earn enough to afford higher quality housing. Cheaper housing and neighborhoods often bring further exposures to toxic chemicals.
- Chronic pain causes lack of sleep and frequently causes depression. These, in turn, can promote inflammation and immune system dysfunction that underlies tumor progression and other illnesses.
Beneficial feedback loops:
- Supporting local food production and farmers markets can improve the economy, access to nutritious food, and social cohesion, all of which can contribute to better health, a better economy and improved quality of life.
- Moving more can contribute to weight loss, better sleep, better stress management, better digestion, and generally feeling better, which may then promote further physical activity and wellness.
- Managing stress responses can set the stage for better sleep; less use of alcohol, drugs (both prescription and recreational) and tobacco; and greater spiritual and relationship wellness and support. These in turn can make managing stress more effective and ultimately reduce disease burdens.
- Pain relief improves quality of life and dampens inflammation, leading to greater productivity at work, less chronic illness, and greater wellness.
Leverage Points
In a causal web, relatively minor changes can have magnified effects downstream.
In a causal web, relatively minor changes can have magnified effects downstream. Even a minor tweak—depending on what (and perhaps where and when) it is—can have multiple benefits or else multiple adverse impacts that cascade throughout much of the system. These are key leverage points. Finding and managing key leverage points can turn whole systems around.
An ecologic model and perspective—the "big picture"—should be valuable in helping someone decide how and where to intervene to improve system function within the context of their own interests, capacities and skills.
Written by Nancy Hepp, MS, and Ted Schettler, MD, MPH; most recent update on October 16, 2019.
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