All mammals, including humans have an innate response to perceived threat or stress. The more common name for it is the “flight or fight” response. Our remote ancestors faced many real threats. Let’s say for example one encountered a saber tooth tiger. As soon as he (or she) saw the tiger, several things happened. Epinephrine and norepinephrine were released, speeding up the heart rate in preparation for running away. A surge of cortisol was also released, which increased glucose in the bloodstream for fuel for muscles and the brain. Cortisol also increases mental alertness. Inflammatory molecules were released to promote wound healing should that be needed.
This kind of acute stress response is a good thing. People or animals with this kind of response were more likely to survive and reproduce. Once the acute threat was over, all the hormones and neurotransmitters quickly returned to their baseline levels.
In today’s world, threats from predators are not a problem for the vast majority of people. The threats we perceive are things like poor work conditions; experiencing discrimination, hate, or abuse; poverty; homelessness; divorce or other family discord; having little control over outcomes; feeling overwhelmed.
These are all things that produce the stress response, but unlike our remote ancestors, these threats are chronic. They are either lifelong or at least last a long time. Instead of returning to normal, the stress hormones and neurotransmitters stay elevated for long periods of time. A chronic stress response is definitely not a good thing!
Allostatic Load
The medical term for the acute stress response is called allostasis. Here is the definition of allostasis from Wikipedia: “Allostasis is the efficient regulation required to prepare the body to satisfy its needs before they arise by budgeting those needed resources such as oxygen, insulin etc., as opposed to homeostasis, in which the goal is a steady state.” Allostasis is an adaptive response to acute stress. Allostatic load on the other hand is the long-term result of failed allostasis, resulting in dysregulation (abnormal function) of multiple systems including the neuroendocrine, cardiovascular, immune, and metabolic systems.
Allostatic load is measured traditionally by 10 indicators of chronic stress. Primary indicators are the hormones and neurotransmitters released by stress. Secondary outcomes are measurements of the systemic effects of the primary indicators. All of these indicators are associated with the perception of stress. Below is a table showing the 10 indicators, how they are measured, and which body systems are affected. Here is a link to the full article from which this table comes: Allostatic Load: Importance, Markers, and Score Determination in Minority and Disparity Populations
| Category | Marker | Functional purpose |
|---|---|---|
| Primary mediators | Dehydroepiandrosterone sulfate (DHEA), serum | Secreted by the adrenal glands. When high with stress it tends to lower cortisol and be protective in the stress response. |
| Cortisol, urinary | Integrated measure of 12-hour hypothalamic–pituitary–adrenal axis activity. Secreted by the adrenal glands. Has multiple effects in stress response. | |
| Epinephrine, urinary | Integrated indices of 12-hour sympathetic nervous system activity. Sympathetic nervous system activation increases heart rate and blood pressure. | |
| Norepinephrine, urinary | ||
| Secondary outcomes | Systolic blood pressure | Indices of cardiovascular activity and major risk factor for vascular disease |
| Diastolic blood pressure | ||
| Waist–hip ratio | Index of long-term levels of metabolism and adipose (fat) tissue deposition. High value means fat around internal organs which increases inflammation and increases LDL (bad cholesterol) and triglycerides. | |
| High-density lipoprotein cholesterol | Index of atherosclerotic risk protection. Low value increases risk of heart disease. | |
| Total cholesterol | Index of long-term atherosclerotic risk | |
| Hemoglobin A1C | Integrated measure of high blood sugar over 2–3 months |
Each indicator that is a certain distance out of the normal range counts as one point. The score can range from zero to ten. The higher the score, the greater the risk of illness or death.
Other Indicators
Although the ten indicators were the ones described in the original papers about allostatic load, other indicators have been used as well.
- Heart rate variability is the normal beat to beat variability in the heart rate. In a healthy heart there is slight variation in the timing of one heartbeat to the next. Chronic stress reduces or even eliminates this beat to beat variation.
- High sensitivity C-reactive protein (CRP). This is a measure of systemic inflammation that can result from chronic stress.
How is the stress reaction triggered?
The stress reaction begins in the brain. Something in the environment is perceived in a part of the front of the brain called the prefrontal cortex. This is the executive decision maker in the brain. If the prefrontal cortex perceives something in the environment as a threat, then it sends messages to the limbic system (the part of the brain that is involved with emotions). It also sends messages to centers lower in the brain, especially the hypothalamus. The hypothalamus sends messages to the adrenal glands which secrete cortisone, norepinephrine and epinephrine. The hypothalamus secretes DHEA. Messages from the hypothalamus are also sent to the white blood cells which secrete inflammatory chemicals called cytokines. All of this prepares the body to deal with the perceived threat. Different people may perceive different things as a threat. It is the reaction to perceived threats that causes allostatic load. If another person experiences the same thing in the environment as not a threat, then there is no stress reaction.
Diseases associated with high allostatic load (high chronic stress)
A high allostatic load score is not disease in itself, but if chronic stress continues then disease in the cardiac, metabolic, neuroendocrine and immune system can occur. Here is a list of diseases associated with persistent high allostatic load.
- Heart disease, primarily progressive blockage of the coronary arteries. This can lead to angina and/or heart attack. Congestive heart failure and arrhythmia like atrial fibrillation can also occur
- Peripheral arterial disease. That is blockage in arteries in the legs and sometime fingers.
- High blood pressure
- Stroke
- Autoimmune diseases like rheumatoid arthritis or lupus
- Diabetes
- Fibromyalgia
- Chronic Fatigue Syndrome
- Dementia or decreased cognitive function
- Depression
- PTSD
- Cancer, particularly breast and ovarian cancer. The increase in cancer is probably related to decreased immune system function
Allostatic Load and Mortality
Many studies have shown that people with persistently hight allostatic load have about a 25% higher premature death rate than people with low allostatic load.
Disparities in Health Outcomes
The response to chronic stress (allostatic load) may explain some of the disparities we see in health outcomes. We know, for example that Adverse Childhood Events (ACE), which include things like abandonment and abuse, increase the risk of many chronic diseases in adulthood. Studies have shown that adults with a history of ACE have high allostatic load scores.
African Americans have higher incidence of many cancers, as well as poorer outcomes from those cancers. They also have worse outcomes from heart disease, high blood pressure and diabetes. While a good portion of these poorer outcomes are related to lack of access to health care, these disparities persist to some degree even in middle class and upper middle class African Americans. Almost all African Americans have experienced or still experience racism on a chronic basis. African Americans of all social classes have higher allostatic load scores than caucasians. Chronic stress and response to it may be the common denominator for these disparities as well as for health outcome disparities in other marginalized populations.
How to reduce allostatic load
There is typically a long time between the presence of indicators of allostatic load and illness and death caused by diseases associated with these indicators. That presents an opportunity to reduce allostatic load before the chronic stress response leads to illness and death. So how do we reduce allostatic load?
Some of the things that cause allostatic load can only be reduced by societal changes. Things like poverty, structural racism and homelessness cannot be decreased by individual effort. Even these causes, though, can respond to the mind body methods discussed below. On the other hand, if you don’t have enough to eat, have no home, or have a job that gives you no control of your life, it is not likely that you will have the energy or the will, or the financial means to do many of the mind body methods discussed below. We should not be distracted from working to decrease the inequities that are responsible for societal causes of chronic stress.
Mind-Body Medicine
Remember that an external threat is first received by the peripheral nervous system and transmitted to the pre-frontal cortex. In order to reduce allostatic load we can either reduce the threat perception in the prefrontal cortex (top down) or reduce the transmission of threat in the peripheral nerves (bottom up).
Top Down Treatments
Top down treatments start with intentional activity in the prefrontal cortex. The idea is to decrease activation of the limbic system and the hypothalamus. This can be accomplished by mindfulness meditation, hypnosis (including self hypnosis), mental imagery and progressive muscle relaxation. All of these techniques when done regularly have been found to decrease allostatic load indicators and to reduce the risk of stress related illnesses.
Bottom Up Treatments
Bottom up treatments decrease the threat transmission to the prefrontal cortex. They include yoga, Tai Chi, massage and biofeedback. These treatments have also been shown to decrease allostatic load and to reduce stress related illness.
Bottom up and top down are somewhat of an oversimplification. All of these treatments have some aspects of both top down and bottom up. Yoga, for example includes aspects of meditation. The same goes for Tai Chi. Biofeedback involves some attention from the prefrontal cortex. Massage also includes progressive muscle relaxation.
Bottom Line
The body’s reaction to a perceived threat includes a complex cascade of messages from the executive center in the prefrontal cortex to multiple body systems including the nervous system, the endocrine system, the cardiovascular system and the immune system. All of these things prepare the body to deal with the threat. As long as the threat is short term the stress response is very useful to the organism.
Perception of chronic stress leads to continuous secretion of all the stress hormones and inflammatory cytokines and this leads to dysfunction of multiple body systems and eventually to illness and death.
Mind body treatments, both top down and bottom up can reduce the allostatic load (chronic stress response) and reduce the risk of stress induced illness and death.
Many causes of chronic stress have to do with the structure of our society, such as poverty, homelessness and structural racism. Individual effort is not likely to ameliorate the effect of these causes of chronic stress. All of us should be working toward societal change to reduce chronic stress response in marginalized populations.