Cortisol and Stress: A Quick Primer

Cortisol is something we can’t live without. It’s a hormone produced by our endocrine system, essential to both our daily functioning and our long-term survival. It has three primary functioons in our body: it helps us eat, sleep, and handle stress. It’s more complex than that, of course. It’s possible to spend years in graduate school studying the action of cortisol and other hormones on the human brain and body. For purposes of this post, however, we don’t need to get bogged down in the details.

We’ll keep the discussion short and to the point.

Cortisol Action: Proactive and Reactive Modes

The Proactive Mode

Cortisol has two primary modes of functioning. One happens in the background and follows a predictable, daily schedule. This first mode, known as the proactive mode, coordinates natural physiological patterns like our waking, sleeping, and eating cycles. It keeps our internal systems running on time. It makes sure our body knows when to rest, when to wake up, when to eat, and when to digest.

Most people know the phrase circadian rhythm. That’s what the proactive mode of cortisol regulates. Our adrenal glands, triggered by our hypothalamus and pituitary gland, release cortisol in what scientists call a diurnal pattern. Cortisol levels peak in the morning, then taper off throughout the day and reach their lowest point in the evening. Everyone experiences this every day. It’s why we have energy in the morning, then roughly twelve hours later, our energy level dips, and we start thinking about bed.

The Reactive Mode

The second mode of cortisol action, known as the reactive mode, controls how we react to acute stress. In this mode, external stimuli trigger cortisol release. When things happen in our environment that require an immediate response, the cortisol response is almost immediate. One second, we’re going about our day, minding our own business. Then an event triggers our internal alarms and our brain springs into action. Our adrenal glands dump cortisol into our bloodstream and suddenly we’re alert and on edge, ready to take whatever action we need to take.

Most people understand this mode of cortisol action as the fight or flight reflex. In evolutionary terms, the fight or flight reflex is one of the things that has kept us alive for thousands of generations. We had it long before we developed the brain power to communicate with language or use tools. The fight or flight reflex gives our body the energy we need when we need it most. Thanks to the cortisol released in the reactive mode, we have the strength to stave off an enemy when cornered or the speed to run from danger until we’re safe.

The problem with humans is that our reactive system doesn’t always turn off when it should – and that can cause problems.

Negative Effects of Cortisol

In his 1994 book Why Zebras Don’t Get Ulcers, bioloigist Robert Sapolsky describes what happens to the human body when it’s exposed to cortisol for extended periods of time: nothing good. We jest, but only in part. That’s basically the message. As to how and why, the book is far more eloquent: it offers an incredibly accurate and concise way of thinking about cortisol and the modern human.

Imagine a prey animal – an antelope or a zebra, Sapolsky suggests – minding its own business one day out on the savannah, munching on some grass. Along comes a predator – and an epic chase ensues. For the prey, it’s a matter of life and death. Fight or flight kicks in. Cortisol floods the bloodstream. It supercharges the physiological systems that help the animal escape, and temporarily shuts down or slows physiological systems that don’t.

The human cortisol response is almost identical. We experience stressful external stimuli and our fight or flight response kicks in right away. The differences between humans and animals appear in what happens next – and those differences are significant. External stimuli can trigger a cortisol response in animals and humans, but in humans, emotional and psychological stimuli can trigger a cortisol response as well. Animals rebound from life-threatening situations very quickly. Minutes after a stressful escapade, a prey animal returns to business as usual. They go back to munching grass like nothing ever happened.

Humans, on the other hand, often take far longer to process stressful episodes. A stress response that lasts for minutes in an animal can last much longer in humans. In fact, a human stress repsonse can last for hours, days, weeks, months, or even years. It’s this chronic exposure to cortisol – and the fact that in humans, a thought, memory, or feeling can trigger a fight or flight response – that can lead to an array of stress-related physical, emotional, and psychological disorders. That’s why it’s important for humans – and that means all of us – to learn practical techniques to handle stress.

You might also want to read: Teen Stress & Anxiety: Know the Signs