I could have easily titled this article as “Chronically elevated stress kills brain cells”. Because cortisol is the stress hormone.
When under stress, the adrenal glands secretes the cortisol hormone which activates our “fight-or-flight response”. Cortisol plays an important role in that respect. And that is fine for short durations.
The problem comes when cortisol is chronically elevated due to constant non-relenting stress. This chronic high levels of cortisol is detrimental to many aspects of the human physiology. But one is when the stress hormone cortisol gets released into the bloodstream, it goes everywhere including the brain.
And brain cells start to die when they are chronically exposed to cortisol. And when brain cells die, the brain shrinks — especially the hippocampus part. Just search “cortisol shrinks the brain” in your search engine.
In the below video, Dr. John Medina says that “stress damages cognition in virtually every way cognition can be measured” …
The article The Brain on Cortisol writes…
“Cortisol is a potent chemical that surges when you slip into stress, and is now recognized as a drug that can literally shrink human brains.”
Dr. Andrew Weil website says …
“Cortisol is directly toxic to neurons, it actually destroys hippocampal cells resulting in loss of the ability to voluntarily recall previously learned information. You can lower cortisol levels with meditation and other relaxation techniques.”
In his book Brain Longevity, Dr. Khalsa writes that …
“If you experience the stress response day after day, year after year, its toxic effects will gradually injure and kill billions of your brain cells.” [page 121]
He believes that …
“I am convinced, based upon my research and clinical work, that excessive cortisol production is one of the primary causes of death of those cells.” [page 8 and 9]
Cortisol Damages the Hippocampus
The memory center of the brain known as the hippocampus is prone to damage by cortisol. In The UltraMind Solution, Dr. Mark Hyman writes that …
“we know that the stress hormone cortisol injures the hippocampus, damages brain cells, and leads to memory loss and dementia. Conversely, we know that reducing cotisol levels with relaxation increases the size of the hippocampus through neurogenesis.” [page 53]
In his other book, UltraPrevention, he writes …
“Cortisol kills neurons, especially in a particularly sensitive area called the hippocampus.”
Cortisol Affects Memory
Because the hippocampus play a crucial role in memory. It is no surprise that chronically elevated cortisol levels will affect memory. In the below video, you can see a report on how stress affects the memory of mice….
Magnificent Mind at Any Age by Dr. Amen writes that …
“They found that older adults with continuously high levels of cortisol performed worse on memory tests than older adults with moderate or low cortisol levels. In addition, older adults with longterm exposure to high cortisol levels also had, on average, a 14 percent smaller hippocampus”
In the book Beautiful Brain, Beautiful You, it says …
“Cortisol, the so-called stress hormone, has been shown in animal studies to actually kill off neurons in the hippocampus, the brain’s memory center. Animals under chronic stress have smaller hippocampi, and there is reason to believe the same holds true for humans.” [page 137]
Patrick Holford in Optimum Nutrition for the Mind talks about studies by Professor Robert Sapolsky …
“In studies with rats he found that two weeks of induced stress causing raised cortisol levels causes dendrites, those connections between brain cells, to shrivel up. He believes that brain cell loss in aging and Alzheimer’s disease may be, in part, due to high levels of cortisol…”
Stress and Depression
There is no doubt that stress can lead to depression. Here is how.
In the book, The Cortisol Connection, it writes …
“The first phase is characterized by an overexposure to cortisol, creating a “toxic” effect whereby too much cortisol actually destroys crucial brain cells responsible for good mood.” [page 23]
The second stage is when the brain become resistant to cortisol as a protection mechanism. Now the cells are under-exposed to cortisol leading to memory and psychological problems.
Further on page 116, it continues …
“… having elevated cortisol levels raises one’s risk of developing depression. It also appears that cortisol does a pretty good job gumming up the works when it comes to the synthesis, transport, breakdown, and overall activity of the neuotransmitters in the brain.”
In summary, cortisol is simply bad for the brain.
Putting Things in Perspective
It is scary to read about brain cells dying. To put things into perspective, one stressful traffic jam for example is not going to cause that large amount of damage to brain cells.
Brain cells consist of neurons and support glial cells. And to be sure, with about 100 billion neurons and even more glial cells, the brain can withstand a loss of some amount of cells.
Doing some math examples, let’s say that a million brain cells dies over the course of a lifetime. One million out of 100 billion neurons is only 0.001%. That means that for every one cell that dies, 99,999 of them lives. And if you count neurons and glial cells as “brain cells”, then that percentage would be at least halved. Even in constructing a worst case scenario, you need to loose 1 billion neurons in order to loose one percent of neurons.
With these numbers in mind, then it would no be surprising to read an article in USC that says “if you don’t have a specific disease that causes loss of nerve cells, then most, if not all, of the neurons remain healthy until you die.”
Other cells such as our skins cells die at a much faster rate. However, skin cells grow back and get replaced at a fast rate too. Not so for brain cells. It is true that the brain can form new cells in a process called neurogenesis in the hippocampus region. But it is quite slow and only in very limited parts of the brain. (By the way, one way to enhance neurogenesis is with aerobic exercise).
Since it is difficult for scientists to count brain cell lost while someone is still alive, it is difficult to say with certainty how much brain cells are lost on a regular basis. And scientist are continually revising their theories.
In any case, it is still a good idea to maintain the survival of as much of your brain cells as possible, and avoid excessive stress-induced cortisol which tends to kill them.