Updated: Nov 5, 2020
Our first post in this series gave us a general overview of stress and some of the effects it can have on our bodies when left unchecked. This post will explore the ins and outs of stress from a biological perspective. We must take a bit of a dive into physiology to understand this next part, so stay with me…
How Does It Work?
Our stress response is governed by our central nervous system, which interacts with our endocrine system. Our nervous and endocrine systems use the hypothalamus and pituitary glands located in the brain, as well as the adrenal glands sitting atop the kidneys, to create the hypothalamic-pituitary-adrenal axis, or HPA axis. This system is the primary driver of bringing our bodies back to balance after experiencing stress. It kicks into gear when we need to adapt to daily stress. It’s one half of our fight-or-flight response.
When we experience stress, the HPA axis fires up. The hypothalamus sends a signal to the pituitary gland via a hormone called corticotropin-releasing factor (CRF), which causes the pituitary to release another hormone called adrenocorticotropic hormone (ACTH). ACTH travels through the bloodstream to reach the adrenal glands, which then releases cortisol. Once enough cortisol has been released, a signal is sent back to the hypothalamus to stop releasing CRF (1, 2).
Cortisol is a steroid hormone produced by our adrenal glands as part of a larger class of compounds known as glucocorticoids. It balances blood sugar, prevents inflammation by lowering immune function, and primes our bodies to fight or flee. This hormone is very important for restoring balance after stress is encountered.
The list of stressors we encounter day to day is long enough to create its own stress. So, our bodies continue to use this short-term answer for the long haul. This is known as resilience. We keep releasing cortisol, and it works as long as our metabolism can keep up.
Metabolic reserve refers to the ability to handle that same workload over longer periods of time, or rather how long our bodies can resist the negative effects of stress. As we lose resilience and deplete our metabolic reserve, we lose our ability to adapt to stress. Recall our earlier point that the ability to adapt to stress has been linked to protection from certain serious diseases and disorders.
What Creates the Problem?
Now that we’ve talked about all the ins and outs of stress, let’s talk about what creates HPA axis dysfunction.
1. Perceived Stress. The most obvious cause is the stress we know and have mentioned multiple times so far. Those stressors dealing with mental and emotional triggers are usually the ones we recognize.
2. Blood Sugar Imbalances. Remember, one of cortisol’s main duties is to help regulate blood sugar. We drastically impair that system when we skip meals and/or eat lots of high-sugar foods. The constant roller coaster of raising and lowering our blood sugar creates high demand for more cortisol to be released. Those who have insulin resistance or hypoglycemia are especially susceptible.
3. Lack of Sleep. Cortisol, along with melatonin, also plays a large role in our sleep-wake cycle, aka circadian rhythm. In fact, cortisol is responsible for waking us up in the morning; low cortisol levels at night help to stimulate melatonin production for sleep. So, our cortisol should be highest in the morning and lowest at bedtime. When we don’t get enough sleep or have abnormal sleeping patterns, our ability to regulate that rhythm is impaired. We disturb a carefully-measured and controlled system by forcing more (or less) cortisol into the fold.
4. Inflammation. This one is often forgotten. As we discussed earlier, cortisol has a big hand in reducing inflammation. Chronic inflammation from overtraining or poor athletic recovery can create poor adaptation. Also, inflammation stemming from overgrowths of opportunistic bacteria in the GI tract is an insidious contributor.
The stress response is a very indiscriminate system. It treats every stressor the same: excite the HPA axis and fight the stress with cortisol. But with more stress comes the need for continuous activation. Being constantly bombarded with all these avenues of stress creates an exaggerated stress response. Our body will eventually hit the wall with this pace. We will either exceed the metabolic reserve or stop responding to cortisol as well, essentially becoming desensitized.
Have you ever had issues with fertility? How about weight control? Or perhaps anxiety or depression? These are all areas that could be affected due to HPA axis dysfunction and the inability to adapt to stress.
Our final post in this series will cover the strategies to help calm an abnormal/exaggerated stress response. How do we pull ourselves out of the constant fight-or-flight state?