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By Root 1001 0

’s second protection system is the immune system, which protects us from threats originating under the skin, such as those caused by bacteria and viruses. When the immune system is mobilized, it can consume much of the body’s energy supply. To get a sense of how much energy the immune system expends, recall how physically weak you become when you are fighting infections such as a flu or a cold. When the HPA axis mobilizes the body for fight or flight response, the adrenal hormones directly repress the action of the immune system to conserve energy reserves. In fact, stress hormones are so effective at curtailing immune system function that doctors provided them to recipients of transplants so that their immune systems wouldn’t reject the foreign tissues.

Why would the adrenal system shut down the immune system? Imagine that you are in your tent on the African savannah suffering from a bacterial infection and experiencing a bad case of diarrhea. You hear the gutty growl of a lion outside your tent. The brain must make a decision about which is the greater threat. It will do your body no good to conquer the bacteria if you let a lion maul you. So your body halts the fight against the infection in favor of mobilizing energy for flight to survive your close encounter with a lion. Therefore, a secondary consequence of engaging the HPA axis is that it interferes with our ability to fight disease.

Activating the HPA axis also interferes with our ability to think clearly. The processing of information in the forebrain, the center of executive reasoning and logic, is significantly slower than the reflex activity controlled by the hindbrain. In an emergency, the faster the information processing, the more likely the organism will survive. Adrenal stress hormones constrict the blood vessels in the forebrain reducing its ability to function. Additionally, the hormones repress activity in the brain’s prefrontal cortex, the center of conscious volitional action. In an emergency, the vascular flow and hormones serve to activate the hindbrain, the source of life-sustaining reflexes that most effectively control fight or flight behavior. While it is necessary that stress signals repress the slower processing conscious mind to enhance survival, it comes at a cost … diminished conscious awareness and reduced intelligence. (Takamatsu, et al, 2003; Arnsten and Goldman-Rakic 1998; Goldstein, et al, 1996)

Fear Kills

Remember the shell shocked, frozen look on my Caribbean medical students’ faces when they failed my test, the medical school equivalent of a voracious lion? Had my students stayed frozen in fear, I can guarantee you that they would have performed dismally on their finals. The simple truth is, when you’re frightened, you’re dumber. Teachers see it all the time among students who “don’t test well.” Exam stress paralyzes these students who, with trembling hands, mark wrong answers because in their panic, they can’t access cerebrally stored information they have carefully acquired all semester.

The HPA system is a brilliant mechanism for handling acute stresses. However, this protection system was not designed to be continuously activated. In today’s world, most of the stresses we are experiencing are not in the form of acute, concrete “threats” that we can easily identify, respond to, and move on. We are constantly besieged by multitudes of unresolvable worries about our personal lives, our jobs, and our war-torn global community. Such worries do not threaten our immediate survival, but they nevertheless can activate the HPA axis, resulting in chronically elevated stress hormones.

To illustrate the adverse effects of sustained adrenaline, let’s use an example of a track race. An extremely well-trained and healthy group of sprinters step up to the starting line. When they hear the command: “On your mark!” they get on their hands and knees and adjust their feet into the starting blocks. Then the starter barks out, “Get set.” The athletes’ muscles tighten as they prop themselves up on their fingers and toes. When they shift into “Get