Cortisol Stress Hormone Kills Brain Cells by the Millions

Whenever a person is under stress, the stress hormone cortisol gets released into the bloodstream, which goes everywhere including the brain.

More precisely, the mechanism goes like this...

1. ARH (adrenocorticotrophic releasing hormone) is secreted by the hypothalamus.
2. ARH causes the pituitary gland to produce ACTH (adrenocorticotrophic hormone)
3. ACTH in turn cause the adrenal gland to produce adrenaline (hence its name) and cortisol.
4. This then results in increased blood pressure and heart rate.^[1]

Cortisol harms and sometime kills brain cells in three ways:

1. It interferes with brain's supply of glucose.
2. It interferes with the function of neurotransmitters.
3. It causes influx of calcium into brain cells.^[2]

"Cortisol killed brain cells by the millions." These were the words spoken by Dr. Dharma Singh Khalsa when he gave a talk about brain longevity at the Chautauqua Institution in New York state^[3].

Dr. Khalsa refers to the relationship between cortisol and memory as the "Cortisol Connection" in his book Brain Longevity. There he goes further to say that brains cells injured and killed could be in the billions. He writes ...

"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]

It is scary to read that a such large numbers of brain cells die. We have to keep in mind that this is over the course of a lifetime. That number is only a guess or estimation, because it is hard to image opening up a brain to count the cells at the beginning of life and then at the end of life to compare. Scientist may use extrapolation from mouse models.

To put things into perspective, one stressful traffic jam for example is not going to cause that large amount of damage to brain cells. The quotes mentioned above referring to brain cell death due to various stresses accumulated over a course of a lifetime. And the "billions" number includes both cell injury and cell death.

Brain cells consist of neurons and support glial cells. It is unclear whether the quotes mentioned are in reference to neurons or to 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 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.

(A million sounds like a big number. But a billion has 1000 millions in it.)

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."^[4]

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 quite slowly in comparison. (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.

Dr. Robert Sapolsky is a neuro-biologist at Stanford University and author of the book Stress, the Aging Brain, and the Mechanisms of Neuron Death in which he writes about "how regulation of glucocorticoid secretion fails during aging, producing excessive secretion of these hormones, and how an only recently recognized consequence of that glucocorticoid excess is damage to the brain."^{[page 8]}

Glucocorticoids are a class of steroid hormones in the body and cortisol is a main player among them. The book Stress, the Aging Brain, and the Mechanisms of Neuron Death is actually quite technical. Dr. Sapolsky wrote another book that is more geared for the general public that goes by the fun title Why Zebras Don't Get Ulcers.

An article in "The Franklin Institute" says ...

"The renowned brain researcher, Robert M. Sapolsky, has shown that sustained stress can damage the hippocampus, the part of the limbic brain which is central to learning and memory. The culprits are "glucocorticoids," a class of steroid hormones secreted from the adrenal glands during stress. They are more commonly know as corticosteroids or cortisol." ^[5]

Still don't believe that stress kills brain cells. See these references:

Page 137 soapbox titled "Brain Stress" in the book Beautiful Brain, Beautiful You 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 53 of "The UltraMind Solution" by Mark Hyman ..

"stress hormone cortisol injures the hippocampus, damages brain cells, and leads to memory loss and dementia. Conversely, we know that reducing cortisol levels would relaxation increases the size of the hippocampus through neurogenesis." [page 53]