Cortisol is widely known as the stress hormone. It’s needed in sufficiently high amounts in the morning to wake us up and in low quantities throughout the day so we can fall asleep at night.
Unfortunately, many of us are victims of untimely cortisol excess. But what causes high cortisol levels at the wrong time (read: in the latter half of the day)? Are there any implications for your everyday life? Most importantly, what can you do to dial down the cortisol volume?
Read on to find out the answers to all of your pressing questions so you can start feeling and functioning at your best.
Cortisol is a glucocorticoid, which is the fancy scientific term for steroid hormones. It’s more commonly known as the “stress hormone,” as it regulates cellular metabolism of proteins, carbohydrates, and fats, and activates energy utilization in times of stress.
Due to cortisol’s long half-life in the bloodstream, it’s said to be the body’s long-term response to stress. Meanwhile, adrenaline (another stress-related hormone) has a more immediate, short-term response to stress.
The production of cortisol takes place in the adrenal glands. These glands are part of the hypothalamic-pituitary-adrenal axis (HPA axis), which comprises the hypothalamus and the pituitary gland, both of which reside in the brain.
You can think of the HPA axis as the headquarters for the central nervous system and endocrine system that regulate the hormone cortisol production within your body. The hypothalamus secretes corticotropin-releasing hormone (CRH) that tells the pituitary gland to release adrenocorticotropic hormone (ACTH). This, in turn, stimulates the manufacturing of cortisol in the adrenal cortex.
Aside from intermittent stressors that trigger the fight-or-flight response (the secondary mechanism of cortisol secretion regulated by the circadian clock), did you know that your body’s cortisol production follows its own circadian rhythm?
Normal individuals with a healthy functioning cortisol rhythm have cortisol levels that reach their lowest point at midnight, followed by a build up overnight to peak first thing in the morning. Cortisol volume is typically high when you wake up and surges for 50-60% in the first 30-45 minutes after you’ve awakened. This is called the cortisol awakening response (CAR).
The cortisol load then drops rapidly past this early morning spike before gradually declining throughout the day to reach its minimum level around bedtime so you can wind down and go to sleep.
Scientists call this everyday phenomenon the cortisol diurnal rhythm or cortisol circadian rhythm. If you’re wondering who is the conductor of this rhythm, the suprachiasmatic nucleus (SCN) in the hypothalamus, which is also the principal circadian clock of the brain, acts as the catalyst for cortisol production via the HPA axis.
Across 24 hours, the normal range for healthy salivary cortisol levels (measured in nanograms per deciliter) looks like this:
If your cortisol test results exceed the bracketed values above, you’re likely facing an unhealthy cortisol surplus.
High cortisol levels in the predawn hours (courtesy of your body’s CAR) give you the biological edge to transition into wakefulness. After all, we need all the help we can get to beat the morning sleep inertia. Plus, the early morning cortisol surge supercharges your alertness levels, boosts your immune system, as well as regulates your metabolism and stress response to start your day on a productive note.
On the flipside, a low CAR predicts fatigue later in the day, possibly irrespective of how much sleep you had the night before. That said, you don’t want your cortisol levels to be continually high past the morning spike. Unfortunately, several factors cause an ill-timed cortisol excess as you will see below.
Cortisol naturally declines throughout the day when you’ve met your sleep need, the genetically determined amount of sleep your body needs. Unfortunately, partial or total sleep loss (also known as sleep debt) hikes up your daytime cortisol levels by a whopping 37-45%!
That’s because sleep — especially deep sleep — naturally suppresses cortisol synthesis. As such, sleep insufficiency is one of the main instigators behind excess cortisol secretion. A recent 2021 scientific review shared that several studies “show an increase in the afternoon or evening cortisol levels” when participants only had 5.5 hours of sleep or less.
Not getting enough shut-eye then triggers a vicious cycle of sleep loss and cortisol surplus. In fact, just short-sleeping for one night is enough to inflate your cortisol levels the following evening while delaying cortisol production.
The result? Your body is suffused with excessively high cortisol levels at an even later time, postponing your target bedtime which further cuts into your sleep duration. As you can imagine, this adds to your sleep debt.
It’s a no-brainer that stress induces cortisol synthesis (a stressor activates the fight-or-flight mechanism telling your body to release the stress hormone). While this is beneficial in small amounts, chronically high doses of stress mean your stress response system is stuck in the fight-or-flight mode all the time.
Under normal circumstances, sufficient cortisol volume in the body initiates a negative feedback loop that tells the HPA axis to switch off cortisol production. In the case of chronic stress, your body is constantly flooded with high levels of cortisol. Over time, this damages the built-in negative feedback mechanism. Even when the stressor disappears, your body maintains the chronically high cortisol levels such that you have no escape route from the glucocorticoid overload.
The result is a vicious cycle of chronic stress and excess cortisol.
Remember when we explained how the SCN runs a tight ship with regards to your cortisol rhythm? Any disturbances to your internal clock are enough to throw your body’s cortisol rhythm off course. Everyday examples of circadian misalignment include travel jet lag, social jet lag, and shift work.
Intermittent circadian misalignment like shift work and jet lag may invert the normal cortisol rhythm, subduing the cortisol awakening response and raising pre-bedtime cortisol levels.
Meanwhile, per the earlier 2021 review, circadian misalignment in the short term “shifts the timing of the peak of the cortisol rhythm by less than 30 min.” Interestingly, minute amounts of chronic circadian misalignment varied the peak cortisol timing but reduced the overall cortisol volume generated in the body.
This correlates with another 2015 study that confirmed circadian rhythm disorders like advanced sleep phase disorder lowers cortisol levels through an unknown mechanism.
From a medical perspective, chronically high levels of cortisol are characteristic of a health condition called Cushing’s disease or Cushing’s syndrome. It may be caused by:
Other possible causes of high cortisol levels include kidney disease and an underactive thyroid.
Science also warns that moderate to high-intensity workouts heightens the cortisol load in your bloodstream. On the other hand, low-intensity exercises don't significantly increase cortisol levels, and in fact, lower the overall cortisol volume. The researchers noted that fitter individuals tend to have a “higher intensity threshold necessary to provoke an increase in cortisol” than those who lead a sedentary lifestyle.
So, what happens to your body’s excess cortisol after an intense gym session? Too-vigorous physical activity mistakenly triggers your brain’s protective mode, even when you’re resting. This further highlights the importance of sleep as a post-workout recovery measure to dampen the cortisol influx, especially if you constantly engage in intense workouts like high-intensity interval training (HIIT).
The signs of high cortisol levels (otherwise categorically known as symptoms of Cushing’s syndrome) usually include:
If you experience any of the above symptoms, your doctor may recommend specific blood tests like the dexamethasone suppression test for an in-depth diagnosis.
Untimely high cortisol levels don’t just affect your sleep and body clock; they impoverish your overall health and wellness.
We’ve mentioned how the SCN functions as a master clock that the cortisol rhythm ticks to. But the SCN doesn’t only control the circadian rhythm for cortisol secretion, nor does the stress hormone only interact with the central circadian clock.
Aside from the master clock, peripheral clocks are present across all organs and tissues in your body — think the liver, gut, pancreas, kidney, and muscles. These clocks fall under the influence of the SCN, with cortisol as the key metabolic signaller. Because cortisol receptors are found in almost every tissue, the hormone can directly interact and synchronize these peripheral clocks with the SCN.
As the earlier 2021 review explains, “changes in the cortisol rhythm may alter the timing and coordination of metabolic processes throughout the body.” In fact, the same review warns that an excessive amount of cortisol paves the foundation for increased insulin resistance that may heighten the odds of high blood sugar levels over time. A cortisol overload also diminishes physical performance and neurocognitive functioning.
Another 2014 study warned of a strong association between high cortisol levels and heart disease. Other scientific evidence indicates prolonged cortisol hypersecretion is a “biological risk factor” for mental health illnesses like depression. More alarming data explained that a disrupted cortisol rhythm suppresses the immune system and over-excites the inflammatory response, both of which can activate tumor growth within the body.
But the repercussions of an out-of-tune cortisol rhythm don’t stop here. As you will remember, untimely high cortisol levels often trap you in the endless loops of sleep loss and chronic stress, each with its own ill effects.
On the topic of sleep insufficiency, acute sleep debt downgrades every aspect of your life — emotionally, cognitively, and physiologically — the very next day. When sleep debt persists over months and years, it transforms into chronic sleep deprivation that comes with its own baggage of health issues. For instance, obesity, weight gain, and cardiovascular illness — not unlike those directly associated with cortisol hyperactivity.
Meanwhile, prolonged exposure to stress doesn’t just spike your heart rate or tense your muscles. Chronic stress sets off a plethora of medical problems such as:
For these reasons, it’s imperative to keep your cortisol levels in control to thwart the multitude of health complications awaiting you.
Medical causes aside, sleep deprivation, high stress, circadian misalignment, and high-intensity exercise are the usual culprits behind excess cortisol production. To reduce high cortisol levels, you have to tackle these root causes of the problem.
That’s why we recommend:
High cortisol levels may not necessarily be a bad thing. It’s only when cortisol production remains high after the early morning spike that you need to watch out for.
Various factors can cause high cortisol levels. But the biggest culprits on the list are sleep insufficiency, chronic stress, circadian misalignment, high-intensity exercise or overtraining and certain medical conditions like Cushing’s disease.
Before you consult your primary doctor, the RISE app is worth a try to keep your sleep debt low, your stress levels in check, and your body clock aligned.
Low cortisol levels manifest as adrenal insufficiency, of which there are three types:
Low cortisol levels manifest as adrenal insufficiency, of which there are three types. Primary adrenal insufficiency (aka Addison’s disease) occurs when the body mistakenly attacks the adrenal cortex, causing autoimmune adrenalitis. Secondary adrenal insufficiency occurs when the pituitary gland fails to produce enough adrenocorticotropic hormone (ACTH) to stimulate cortisol production. Tertiary adrenal insufficiency occurs when the hypothalamus fails to produce enough corticotropin-releasing hormone (CRH) to activate ACTH synthesis.
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