What is “Stress”?

Stress of LifeDo you think of “stress” as everything you have to find time for each and every day? Trying to do ten things, when you only have time for seven! Most people think of stress as all the events in their life, their activities, or as the fast pace of our lives.  But this is NOT the definition of stress that helps us understand health risks, like heart attacks.

Medical researchers define “stress” as the body’s response when confronted with danger or change. “Stress” is a survival reaction wired into the body, NOT the daily background level of activity (even if it is very busy activity). It is the special ‘kick in the pants’ that your brain gives your body, to push it to do more in situations of ‘danger’.  And this idea, that your body (when stressed) is NOT THE SAME on the inside as when it is relaxed, is the key idea in this article.

Fifty years ago the father of stress studies, Hans Selye (1), described stress as the cascade of body reactions that follow an ‘alarm’ signal that your brain gives your body. It is the internal changes IN the body (in situations of ‘danger’) that are critical, not your greater activity. Doing more is actually GOOD for your heart, NOT bad: BUT ONLY IF you successfully complete the task(s) and take the time to celebrate your success. When you enjoy your success you turn OFF the alarm signal.

“Stress” Defined

Acute Stressor: This is a one-time challenge, like when you are given a rush report to write at the end of the day, hearing your boss say, “We HAVE to get this out tonight”; feeling a surge of energy, heart thumping, and working overtime to get the job completed. An acute stressor is a one-time event that you may not face again for months.

 Stress Reactions: These are all the body’s responses to any acute stressor: these are powerful body reactions which occur in a sequence described by Bruce McEwan (2) in his book, The End of Stress as we Know It. The response begins with an alarm signal sent from the brain and results in a surge of activity in the nervous system which alerts all organ systems in the body.

The next key step is activation of the “HPA” axis, the backbone of the stress response. What is “HPA”?  It means the Hypothalamus-Pituitary-Adrenal system, and it involves three organ systems: the brain (the Hypothalamus, which pushes the “battle stations” button); relaying the message to the Pituitary gland, which sends out hormonal signals through the blood) to the Adrenal  gland, which releases stress hormones (adrenalin and cortisol). These stress hormones switch the body into a “battle stations” mode.

Cortisol allows the body to stay in a sustained battle stations mode (to handle the persistence of increased demands from the environment) that can last for months. Cortisol tells the body to release energy stores into the blood and your metabolism changes. Your body will automatically seek to take in more energy (do you find yourself munching more when you are stressed?) AND it tells the body to store more fat.

The activity in the HPA axis also stimulates the immune system, resulting in ‘inflammatory’ reactions.  In the effort to keep your body alert to danger, your body is less responsive to insulin, and the normal cycle of rest (through a deep refreshing sleep), and more activity across the day, is flattened. When stressed, people report trouble falling asleep, then feeling fatigued, and not get everything done during the day.

Chronic Stressor: When acute danger signals become persistent or constant, stress reactions stay turned on. Despite your best efforts to change the stressors, these stressors keep pushing you, and pushing you, and the emergency “battle stations” call of stress hormones becomes a daily drone.

When researchers investigate stress, they want participants to understand they are asking specifically about stress with underlying physiological activation. An excellent example of how this is done would be the INTERHEART study, which defined stress as “feeling irritable or filled with anxiety, or as having sleeping difficulties as a result of conditions at work or at home”.

How do stress reactions become damaging to your heart?

What is NOT appreciated is that this stress system was designed to be used IN EMERGENCIES ONLY. It was designed as a backup system in situations of great danger or change. It was NOT meant to be activated on a daily, or even weekly, basis.

When stresses shift from occasional ‘acute’ challenges to a constant demand, the body bears a burden. Bruce McEwan (1) described this initial burden (a challenge that mobilizes the body’s best efforts) as an “allostatic” response. The stress response is initially adaptive and good, for the body and the heart. An example is the boost in blood pressure when the stress system is activated: this gets more blood to all your muscles.

But, as Hans Selye pointed out, IF these efforts do NOT accomplish a resolution (and termination of the stress) and the body systems continue in high alert, the body systems will reach an ‘exhaustion’ stage and begin to break down. Bruce McEwan called this allostatic “load”, which is irreversible change in the body. Good examples are chronic high blood pressure, high cholesterol, and blockages in the arteries.

 The Heart is vulnerable to Stress

When muscles are working, they contract and release. When they are resting they do not fire at all. But, by this definition the heart gets no rest – ever (at least not in the way your other muscles do).

Remember, your heart has to keep pumping day and night, because that is what keeps you alive.  So how does the heart “rest”? It’s ‘rest’ is the period of relative quiet, at night, which allows it the chance to slow down and recover (2). This is what will allow you to rise to the added demands you will face tomorrow.

But when you are stressed, these opportunities to slow down, to ‘hit the brakes’, and rest and recover at night, are undermined because your body is still in “battle stations” mode. It still thinks there is danger out there that you must be ready for. So it DOES NOT want to allow rest and recovery.

 A Foundation for Understanding Heart Risks

To conclude, your body (when stressed) is not the same ON THE INSIDE as when it is relaxed.  All of these nervous, hormonal and immune changes maintain a DEFENSIVE POSTURE that the brain thinks it needs because of coming dangers. Stress interferes with the usual “rest and digest” response that allows recovery, rebuilding, and rejuvenation of the heart at night (3).

Across years and years, the increased stress load results in irreversible damage to the heart: either buildup of plaque in arteries (heart disease) or electrical problems (arrhythmias). For this reason assessment and management of stress and sleep problems are suggested for management of all patients with heart problems (4).



(1)  Hans Selye (1956) The Stress of Life. New York: McGraw-Hill, 1956.

(2)  Bruce McEwen and Elizabeth Norton Lasley (2002) The End of Stress as We Know It. New York: National Academies Press.

(3)  Michael J Sole and Tami A Martino. (2009) Diurnal physiology: core principles with application to the pathogenesis, diagnosis, prevention and treatment of myocardial hypertrophy and failure. J Appl Physiol. 107: 1318-27.

(4)  Peter Prior, Judith Francis, Jaan Reitav and James Stone (2009) Behavioral, Psychological, and Functional Issues in Cardiovascular Disease. In Canadian Guidelines for Cardiac Rehabilitation and Cardiovascular Disease Prevention. James Stone (Ed.) Winnipeg: CACR. Chapter 6, 107-202.

Dr Reitav is a clinical psychologist working with heart patients at the Cardiac Rehab Program, Toronto Rehabilitation Institute, University Health Network in Toronto, and is a Behavioral Sleep Medicine specialist. He was a contributing author to the chapter on Behavioural, Psychological and Functional Issues in Cardiovascular Disease in the Canadian Guidelines for Cardiac Rehabilitation, which provided clinical guidelines for assessing and treating stress and other psychological difficulties in heart patients.

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