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The nervous system monitors external environmental signals, interprets them and organises appropriate responses for survival. Through the five senses the sense of touch and taste for close-range danger and the sense of smell, hearing and sight for distant danger - the brain is continuously alert for signs of impending threat.
When an imminent danger is perceived, the brain initiates a series of hormonal activities, whose net outcome is that the adrenal glands (situated above the kidneys) will release three "stress hormones" - adrenaline, noradrenaline and cortisol. These hormones work together to help the body either fight the danger, or run away (that is, take flight) from it. Thus, the response is popularly called the "fight or flight" response.
Stress hormones are essential for protection. But they switch off the body's growth and reproduction modes. If the stress is short-lived, the impact is temporary and the growth mode is quickly restored. With chronic stress, the impact prevails and the consequences could be serious.
In modern times, we rarely face acute life-threatening situations, unless maybe when we encounter a robber or a murderer. We are more likely to suffer chronic low-intensity stress from problems that we find hard to resolve such as work-related and personal relationship problems. City living further exposes us to crowds, poor quality air, bright lights at night, loud noises. electromagnetic radiation and other unnatural situations.
These are all stress factors. They do not threaten our immediate survival, but they still activate the fight or flight response. We are continually producing stress hormones. Today, almost all major acquired diseases are linked to chronic stress.
Let's take a closer look at what happens when the body is faced with stress.
Diversion of blood flow
Whether you fight or take flight, you need to use your muscles. So one of the first outcomes of the fight or flight response is that blood is diverted to nourish your muscles, away from the organs. In turn, this lower appetite decreases nutrient supply from intestines and reduces vital reserves. Overall, it inhibits the growth mode. Your chances of short-term survival may improve, but your health suffers and the final effect weakens your dances of long-term survival
When faced with acute danger, you also need a fast, instinctive reaction when you are about to be attacked by a wild animal, for example, it is not a time for reasoning or logic. You have to decide quickly whether to fight or to run fast!
So blood is diverted from the forebrain, which executes reasoning and logic, to the hindbrain, which executes reflex activity. In that moment of danger, you lose your clear thinking and conscious action. You react instinctively. When this keeps happening over a long period, you end up with poorer memory, awareness, learning and intelligence You become less capable of long-term survival.
Elevated levels of stress hormones, especially cortisol, also inhibit the growth of nerve cells in the brain, causing your brain to shrink. This leads to brain ageing and depression Two regions of the brain are particularly affected
- Hippocampus- a brain region associated with memory and spatial navigation Damage of the hippocampus leads to Alzheimer's disease, with symptoms such as memory loss and disorientation;
- Prefrontal cortex- a brain region associated with planning and decision-making expression of personality and moderating social behaviour
Cortisol, one of the two key stress hormones, produces a number of adverse effects, it can
- Lower your level of serotonin, making you feel depressed, anxious and aggressive;
- Increase your yearning for "comfort foods like cakes and sweet desserts. Such foods increase your dopamine and adrenaline to combat mental stress but they also make you put on weight;
- Increase your resistance to insulin and leptin, two hormones that play key roles in metabolism. The final effect increases your risk of obesity;
- Produce more cortisol to fight stress, which also reduces the synthesis of sex hormones such as DHEA and testosterone. This lowers your sex drive and fertility.
You must learn to manage your chronic stress in order to switch off your protective mode and to enter your growth-and-reproductivity mode for health. Appropriate dietary changes will help balance your hormones and support your fatigued adrenal glands.
This content is adapted, with permission, from Book 1 of 2 : The Wonders of Nutrition by Dr Ang Poon Liat. MBBS, M.MED (PAED), MRCP (UK PAED), FAMS, MD.