How stress can kill: The HPA Axis & Cardiovascular Disease (CVD)

This material was in the first draft of “Stress: A Student’s Guide to IB Health Psychology.” It was removed from the final edition and the information is here instead as extra optional content for extended and/or interested students.

What is stress?

In laboratory experiments stress can also be measured in multiple ways, including physiological responses to the Trier Social Stress Test (TSST) like cortisol levels, heart rate, and blood pressure and self-reported stress levels as measured with the Perceived Stress Scale (PSS) questionnaire. But stress is difficult to define because it includes many aspects, including the stressor, the stress response and our thinking (appraisals). Any one or all of these things can be considered “stress”.

A good definition of stress, therefore, is that stress occurs when we experience a threatening stimulus that we feel we can’t cope with. This results in an emotional, behavioural and biological stress response (Lazarus and Folkman, 1984; Fischer et al., 2016). Now that we know what stress is and how it’s measured, the next goal is to understand its causes. If we can understand its causes, we might know how to reduce our stress levels.

Stress is when we experience a threatening stimulus that we feel we can’t cope with, which results in an emotional, behavioural and biological stress response (Lazarus and Folkman, 1984; Fischer et al., 2016).

Read more:

• Stress and the Hippocampus
• Example Exam Essay: Prevalence rates of one health problem (IB Health Psychology)
• Cognitive explanations of one health problem: Appraisals and stress

The physical changes we experience when stressed are beneficial in the short-term, but cause major health problems in the long-term.

What makes something stressful? Stressors

When we ask the question “what causes stress?” we could answer it with one word: stressors. More stressors equals more stress. Therefore, the key to less stress is to avoid stressors. It’s that simple, right? Sort of, but not quite. The same stressor can have different effects for different people. Stressors can also vary in their intensity. Think about the possible sources of stress in your life – when does a harmless event become a stressor?

Sapolsky (2010) outlines four characteristics of psychological stressors:

1. Lack of predictability
2. Lack of control
3. Lack of outlets for frustration
4. The interpretation of the stressor

The more of these characteristics a stressor has, the more stressful it will be.

Stress vs. Anxiety

This focus on specific stressors is also how stress is different to anxiety. Some people use stress and anxiety interchangeably and they are difficult to distinguish. Whereas stress is often caused by an external stressor, anxiety is persistent worry even when there isn’t a specific stressor – it’s an emotional state characterized by a sense of dread or apprehension (apa.org). When you have anxiety, you have a general feeling like something bad is about to happen but you’re not sure why. When you’re stressed, you might have a similar feeling but you know the stressor that’s causing it.

Types of Stress: Acute vs. Chronic

We can further break stress down into two types: acute stress and chronic stress. Acute stress is short-term activation of the stress response, whereas chronic stress is persistent and enduring stressful circumstances that lead to long-term activation of the stress response. Acute stress is perfectly normal and natural with lots of benefits. Chronic stress, on the other hand, has been linked to multiple mental and physical problems. This is why one major “health problem” that we’re explaining in the unit on Stress for IB Health Psychology is chronic stress.

From a biological perspective, chronic stress results in the persistent activation of the HPA axis for an extended period of time.

Cardiovascular Disease (CVD)

Chronic stress is a leading risk factor for cardiovascular disease (CVD). This is another major health problem that we’re going to explain in this unit. CVD is an umbrella term that refers to any disease that affects the heart or blood vessels. Coronary artery disease (having clogged arteries that cause heart attacks), strokes, heart disease and congenital heart disease are all types of CVD. Chronic stress causes biological risk factors for CVD because of the constant activation of the physiological stress response.

Just like melanoma, lymphoma, leukemia, and breast cancer all fall under the umbrella term “cancer”, there are many heart problems that fall under the broad category of cardiovascular disease.

The Physiological Stress Response

The stress response is our body’s biological reaction to a stressor. You might know it by its more common name, “the fight or flight response”. The stress response can begin either externally (bottom-up) or internally (top-down). If we sense something threatening in our environment, our sensory neurons send signals to our amygdala, a small part of the brain that generates negative emotions (like fear and anger). This is where our stress response begins. But this message can get to the amygdala through another route as well. If we think about a particular stressor, our prefrontal cortex can send signals down to the amygdala to activate it and get us ready to fight or flee. Either way, when we’re stressed it means our amygdala is activated.

Chronic stress is a major health problem because it can cause CVD. The difference between acute and chronic stress is duration. However, the distinction between what is considered short-term or long-term stress is subjective and there’s no universal definition.

The HPA Axis

The amygdala sends the signal to the hypothalamus, which triggers the stress response. (Image: Wikicommons).

After our amygdala gets the signal that we’re experiencing a threat, it activates the HPA axis (hypothalamus-pituitary-adrenal axis). This means the hypothalamus alerts the pituitary gland which sends a signal to the adrenal gland. The adrenal gland then releases stress hormones, cortisol and adrenaline. The release of stress hormones is why acute stress can be beneficial – they cause a quick release of energy into the bloodstream that energizes our muscles and our brain. Whatever threat we’re facing, we now have an increase in strength and brain power to deal with it.

The above image shows cholesterol plaques in an artery (atherosclerosis). The top artery is healthy, while the middle & bottom arteries show plaque formation which eventually leads to the artery rupturing, clothing and preventing blood flow.

How does chronic stress cause CVD?

When you think of chronic stress, think of it as a persistent activation of the HPA axis for an extended period of time. As you can see above, acute stress has benefits. The release of cortisol and adrenaline during an acute stressor is a healthy adaptation. The problem is, however, when the HPA axis is continually activated and we’re chronically stressed. This results in high blood sugar, high blood cholesterol and increased levels of cortisol in the blood, as well as high blood pressure (hypertension). These are all leading causes of CVD because they cause a build-up of plaque in the artery walls. This is one way that chronic stress can cause CVD and it’s why every medical physical check-up includes measuring your blood pressure, blood sugar levels and cholesterol levels.

Chronic stress can cause cardiovascular disease, the leading cause of death around the world!

Adrenaline or epinephrine? These are the same hormone; it’s just in some countries (e.g. America) people say epinephrine and others say adrenaline. Similarly, the neurotransmitter noradrenaline is the same thing as norepinephrine just called a different name.

When the IB Guide states that stress is a “health problem”, we need to be more specific. Acute stress is healthy, normal and beneficial. It is chronic stress that is the real problem. This is because in small doses, cortisol and adrenaline are good for us. But in excess, they are dangerous because they create a series of physical risk factors for CVD.

Travis Dixon

Travis Dixon is an IB Psychology teacher, author, workshop leader, examiner and IA moderator.