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Improve Your Health by Fine Tuning Your Cortisol Awakening Response (CAR)

juni 08, 2022

Every morning at around the same time, you wake up. It does not matter if you’re in a room with no light, you still wake up at a consistent time. But how does this happen? What causes your body to “know” when to wake up?

The hormone cortisol plays an important role in our response to stress. The purpose of cortisol is to prepare our body for fight or flight. It increases our blood pressure, pulse rate, and breathing, enhances alertness, causes a rise in blood glucose, and ramps up metabolism. When cortisol rises, we are on high alert – a state needed to survive. 

Cortisol is released in response to stress, but also follows a circadian rhythm. At night when we go to bed, our cortisol levels should be low, allowing us to fall asleep. But during the early hours of the morning, a few hours before we wake up, it rises substantially. It rises until it wakes us up, and then continues to rise for another 30-45 minutes.

This morning rise in cortisol is known as the cortisol awakening response (CAR).

The Cortisol Awakening Response and Disease

Much like cortisol prepares us for stress, the CAR prepares us for the day. It promotes alertness and mobilises energy so that our brain, muscles, and other organ systems function properly. It also has a role in regulating our mood, immune function, and digestion, so guess what we see a lot at Nordic Clinic? Yes, a dysfunctional CAR!  

In research we also see that the CAR is altered in a few disease states. It is blunted in diabetes mellitus1, fibromyalgia1, and PTSD2. A lower CAR is associated with greater menstrual symptoms in cycling women.3 Furthermore, an enhanced CAR is associated with a reduced risk of cardiovascular mortality.4

Studies in major depressive disorders are mixed, but generally show a difference in CAR between patients and healthy controls.5 Finally, a study in older individuals finds that a higher CAR is associated with better physical health, and a greater perception of physical and mental health.6

Overall, this is what we see in our clinic – those with a better robust CAR, usually have better outcomes. 

The Cortisol Awakening Response and Stress

Our daily patterns of light exposure, activity, feeding, stress, and social interaction play a role in our CAR. While CAR is an anticipatory response imprinted by consistent daily cues, stress exposures cause a more acute increase in cortisol.

As such, there is a bi-directional relationship between CAR and stress: chronic stress impacts CAR, and CAR impacts our ability to deal with acute stressors. In the short term, acute exposure to stress7 increases the CAR. Additionally, early morning light exposure8, high intensity exercise9, greater physical activity and short-term sleep deprivation also increase CAR10.

When stress becomes chronic, it blunts CAR and can lead to anxiety and an inability to deal with stress.11 This relationship between CAR and exposure to stress plays an important role in our mental and physical health.

Take a look at these three CAR results below. The first (figure 1) you can see the patient values nicely within the normal limits of the test and following the normal rhythm – exactly what we want to see.

The cortisol awakening response

Figure 1

Then look at the second one (figure 2), totally dysfunctional and flatlined – the patient has lost their natural CAR. Normally this means they feel very tired when waking, rely on coffee to ‘get going’ and over the day to stay focused. This patient also had anxiety and brain fog. This was due to many years of too little sleep, building a company and performing at the office, as well as managing family life…plus all the other social pressures on top…sound familiar? 

The cortisol awakening response

Figure 2

Lastly, look at the figure 3, which has a very overactive CAR. This patient was really struggling to get to sleep and wind down at night, due to higher cortisol exposure over the day. This was driven by recent stress.  

The cortisol awakening response

Figure 3

Your Circadian Habits and Stress Management Are Key to a Robust CAR 

Our daily habits play an important role in how we feel. The CAR fine tunes our physiology to wake us up in the morning and prepare us for daily stressors. Consistent patterns of light exposure, physical activity, feeding, social interaction, and stress create a robust CAR.

On the other hand, this same system regulates our immediate response to acute stressors. When stress remains acute and resolves, this improves our CAR, like in example three above. However, when stress becomes chronic, it blunts CAR, making us more poorly equipped to handle stress and more susceptible to poor health, like example two.

Therefore, having a robust CAR improves mood while promoting healthy metabolism, immunity, digestion, and stress resilience. Good circadian habits and stress management are key to improving health through optimising CAR.

This article was originally published as a guest editor post at foodpharmacy.se

By: Graeme Jones, clinical physiologist and CEO at Nordic Clinic Stockholm. 

Published: 08/06/2022


1. https://physoc.onlinelibrary.wiley.com/doi/full/10.14814/phy2.14644

2. https://www.sciencedirect.com/science/article/abs/pii/S0306453020301335

3. https://onlinelibrary.wiley.com/doi/abs/10.1002/smi.3074

4. https://www.sciencedirect.com/science/article/abs/pii/S0306453022000944

5. https://www.researchgate.net/profile/Oliver_Krentzman/publication/352245789_Literature_Review_The_Role_of_Cortisol_Awakening_Response_in_Major_Depressive_Disorder/links/60c0516f299bf1e6b71bb9d4/Literature-Review-The-Role-of-Cortisol-Awakening-Response-in-Major-Depressive-Disorder.pdf

6. https://www.sciencedirect.com/science/article/pii/S016787602100180X

7. https://www.sciencedirect.com/science/article/abs/pii/S0306453018306693

8. https://www.sciencedirect.com/science/article/abs/pii/S0306453018306565

9. https://www.jstage.jst.go.jp/article/jpfsm/11/2/11_59/_article/-char/ja/

10.  https://www.sciencedirect.com/science/article/abs/pii/S0306453021000056

11.  https://pubmed.ncbi.nlm.nih.gov/33680342/

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