From Cortisol to the Vagus Nerve: Why Everyone Wants to “Regulate” Their Nervous System

Swollen face upon waking, tiredness during the day, difficulty sleeping, anxiety, digestive problems, or a feeling of being permanently alert. It only takes a few minutes on social media to find an explanation that seems to fit all of them: high cortisol or a “dysregulated” nervous system.

From that informal diagnosis, a whole repertoire of solutions also emerges. Breathing in a certain way, exposing oneself to cold, stimulating the vagus nerve, or incorporating small routines that promise to help the body leave the supposed “survival mode.” Concepts that until recently belonged mainly to the language of physiology and medicine have become regular protagonists in wellness content. The problem arises when they are used to explain symptoms or recommend solutions without the necessary context.

But these concepts do not come out of nowhere. Stressful situations really activate nervous and hormonal mechanisms, cortisol participates in them, and the vagus nerve is involved in communication between the brain and various organs. The problem arises when a coordination that is originally complex ends up being presented as a universal chain in which each symptom has a single cause and each cause, a quick way to fix it.

What really happens in the body when we are under pressure

When we perceive a situation as stressful, the body activates several responses to adapt to it. Some appear almost immediately and others take longer to develop, but all are part of the physiological response to stress.

The fastest reaction involves the autonomic nervous system, which regulates functions such as heart rate, blood pressure, or digestion without us having to consciously control them. One of its branches, the sympathetic, helps prepare the body to act in response to an immediate demand; the parasympathetic participates especially in rest and recovery processes.

From this come expressions like fight or flight and rest and digest. They serve to simply explain the role each branch plays, although in reality they do not function as two switches alternating between a state of alertness and one of calm. The autonomic system continuously adjusts different functions according to what the body needs at each moment.

Alongside this nervous response, a hormonal pathway is also activated: the hypothalamic-pituitary-adrenal axis. Through a chain of signals, it ends up stimulating the adrenal glands to release cortisol, a hormone that helps mobilize the resources necessary to face that situation.

This better explains why cortisol and “nervous system regulation” often appear together on social media. Both participate in the stress response but represent different mechanisms that work in coordination.

Cortisol is not the enemy

Few hormones have gained as much fame on the internet as cortisol. Cortisol face, “cortisol belly,” foods to reduce it, routines to keep it low… Its association with stress has ended up turning it almost into a substance that should be eliminated.

But we need cortisol to live. It participates in metabolism, helps mobilize energy, and is involved in immune, cardiovascular, and brain processes. Also, its levels naturally fluctuate throughout the 24 hours.

One of the moments when it increases is precisely around waking. The so-called cortisol awakening response describes a rapid increase during approximately the first 30-45 minutes of the morning and has been linked to preparing the body to face the demands of the upcoming active period.

This means that simply saying someone “has high cortisol” leaves out essential information: how much, at what time, for how long, and under what circumstances.

There are diseases characterized by excessive exposure to this hormone, such as Cushing’s syndrome, just as there are disorders in which too little is produced. But tiredness, weight gain, insomnia, or difficulty concentrating alone do not allow knowing what is happening with adrenal function.

When an explanation starts to fit almost any symptom

The success of this type of message is better understood when observing what they try to explain. Fatigue, sleep problems, changes in appetite, or difficulty concentrating are common experiences and, precisely because of that, nonspecific.

Within this context, the so-called “adrenal fatigue” has also become popular, a theory according to which prolonged exposure to stressful situations would end up exhausting the adrenal glands to the point of preventing them from properly producing the necessary hormones.

The Endocrine Society points out that there is no scientific evidence recognizing adrenal fatigue as a disease nor a validated diagnostic test to identify it.

It should not be confused with adrenal insufficiency, a real pathology in which the body does not produce enough cortisol and whose diagnosis requires specific medical tests.

The difference is important because putting an apparently precise label on such general discomfort can be convincing but also divert attention from other possible causes. The problem is not recognizing that a prolonged period of tension influences how we feel, but turning that relationship into an automatic diagnosis.

The vagus nerve, the other wellness star

If cortisol usually appears as something that should be reduced, the vagus nerve has become one of the great promises for regaining calm.

It is part of the parasympathetic system and connects the brain with various organs in the neck, thorax, and abdomen, so it participates, among other functions, in controlling heart rate and digestion.

From this have emerged numerous contents proposing to “activate it” through slow breathing, cold water, massages, singing, or humming. Some of these practices do cause measurable physiological changes, but that does not mean they “reset” the nervous system or work as a universal solution against stress.

Slow breathing is a good example. A meta-analysis of 31 studies with 1,133 participants observed immediate effects on various cardiovascular parameters, such as changes in heart rate variability and a slight reduction in heart rate. There is also evidence of modest effects on blood pressure and some stress-related indicators.

That is, there is a real physiological basis, but the promises circulating on social media usually go much further than the study results.

“Activating the vagus nerve” does not always mean the same thing

The expression can be confusing because vagus nerve stimulation also exists as a medical treatment.

In certain forms of epilepsy and some cases of treatment-resistant depression, devices are used that deliver controlled electrical impulses directly to the nerve. That clinical stimulation is not equivalent to practicing slow breathing, exposing oneself to cold, or performing a relaxation technique at home.

The difference is important because using a medical term does not automatically turn a wellness practice into a treatment. Breathing slowly, exercising, or resting can be helpful without needing to present them as ways to “hack” the nervous system.

Regulating yourself does not mean always staying calm

Much of the success of these trends comes from naming sensations easily recognized by the population: being tired and, at the same time, feeling it is hard to disconnect.

Sustained stress influences health, and learning strategies to cope with it can be useful. But regulating yourself does not mean eliminating any state of activation.

The body needs to speed up the heart when we exercise, mobilize energy in demanding situations, and produce cortisol at the start of the day. The key is not to always remain calm but to be able to activate when the situation requires it and then recover balance.

And perhaps that is the idea lost among so many videos about cortisol, the vagus nerve, and “survival mode”: the body does not need to be constantly rebooted. It needs to be able to change and recover.