The effect of the mind on the body through stress and happiness

There are clear links between the mind, through happiness and stress, and physical health because the brain drives the way the body reacts to external stimuli. When stressed, the body reacts as if it were physically threatened, resulting in various defence mechanisms being activated. If activated too frequently, these mechanisms cause long term health problems believed to include increased exposure to infection, ulcers, cardiovascular disease and cancer. Happiness, on the other hand allows the body to recover from such issues. Increasingly the medical community is accepting the influence of the mind on health, and fields such as Psychoneuroimmunology are growing rapidly.

In this article we'll look at the mechanism for this in some detail.

Stress, Happiness and Health

There are clear links between happiness, stress and physical health. For example Stone, Reed & Neale, (1987) showed that stressors at work weaken the immune system on the day they occur. Pleasant events enhanced the immune system for up to 2 days. A drop in pleasant events predicted increased susceptibility to the common cold more accurately than an increase in unpleasant events.

This makes sense if one sees the body as a holistic system where thoughts release chemicals into the body, in-turn affecting metabolism and immune system function. There are two aspects to this. The first is the workings of the nervous system, in particular the brain, which determines how we feel about things that happen to us. The second is the way the body defends itself when the brain determines that a major issue is in play. This is the stress response, and is triggered by intense events, both distressing and pleasant. Less intense emotions allow the body to continue to work optimally.

The workings of the nervous system

As the brain processes different stimuli, it brings into play different areas of the brain and emits different chemicals, called neurotransmitters, which affect the brain state. Emotional stimulation results in increases in neural activity in the thalamus and medial prefrontal cortex and with activation of anterior and posterior temporal structures. Happiness is distinguished from sadness by greater activity in the vicinity of ventral mesial frontal cortex (Lane et al, 1997).

There are at least 50 different neurotransmitters. Those leading to positive emotions are: ·
- Serotonin, which induces alertness, positive mood and sociability. It acts against depression. Too much of it can result in manic tendencies. ·
- Dopamine, which is believed to activate the links between the amygdala (which determines emotional response) and the frontal cortex (which expresses them). It is important in rewarding the brain for acting on certain stimuli, especially eating, sex and working for food rewards. ·
- Endorphins, which provide feelings of euphoria and reduce pain. These are created by exercise amongst other things. ·
- Noradrenaline, which is involved in arousal. ·
- GABA is an inhibitor that reduces anxiety. It is enhanced by alcohol, which explains why we are more sociable when a little drunk.

The Stress Response

An intense emotional response, or stressor of any kind results in the activation of the sympathetic nervous system. This is typically termed the 'General Adaptation Syndrome'. There are two aspects to this, an initial 'alarm response' to bring the body's defensive forces to bear on a problem, followed by adaptation to continuing stress if the stressor persists. Ultimately, this will lead to exhaustion. It is this prolonged adaptation that is so injurious to physical health.

Activation of the sympathetic nervous system results in (Guyton, 1977):
- Increased blood pressure ·
- Increased blood flow to support large active muscles, coupled with decreased blood flow to internal organs not needed for rapid activity ·
- Increased total energy consumption ·
- Increased blood glucose concentration ·
- Increased energy release in muscles ·
- Increased muscle strength ·
- Increased mental activity ·
- Increased rate of blood coagulation.

Upon completion of the stress response, the same mechanisms bring these factors back to normal.

Incoming signals from a stressor are processed in the Thalamus. It is believed that these signals can be both external, and transmitted via the senses, or internal and transmitted via the bloodstream. They are then assessed in the amygdala, which determines the response, and then to the Hypothalamus which acts on that response to control the wider, autonomic nervous system. The Hypothalamus region of the brain releases hormones including Vasopresin (ADH), 'Corticotropin-releasing factor' (CRF) and thyrotropin releasing factor (TRF). Vasopresin controls fluid loss from the urinary system, and also acts to constrict arteries should blood pressure drop too low. Whilst usually a protection against injury, it adds to the tendency for increased blood pressure. The release of TRF stimulates the thyroid gland (via the pituitary) to release the hormone Thyroxine. This increases the metabolic rate, heightens mental activity, and increases gastric secretions. Thyroxine also makes the body more sensitive to adrenal hormones, compounding the effects of CRF. CRF stimulates the Pituitary Gland in the brain to release the hormone ACTH (adrenocorticothropic hormone). Shortly after the release of ACTH the adrenal glands secrete hormones including cortisol (also known as hydrocortisone), epinephrine (also known as adrenaline) and norepinephrine (also known as noradrenaline).

Generally epinephrine is related to the presence of physical stressors and is present around the emotion of fear. Norepinephrine is related to the presence of mental stressors, and is present around the emotion of anger. Cortisol provides more energy to the body through conversion of body stores into glucose. The secretion of epinephrine and norepinephrine stimulates the sympathetic nervous system resulting in increased blood pressure and blood flow to the muscles. The release of epinephrine can cause the hypothalamus to stimulate the release of more ACTH, thereby increasing the level of epinephrine still further, and in turn potentially stimulating more ACTH in an escalating cycle. This is a major reason why the effects of prolonged stress can be very damaging to overall health.

The continued activation of the sympathetic nervous system may raise blood pressure consistently (long-term hypertension). Activation of the sympathetic nervous sytem also release a chemical called Renin to be released form the kidneys, which in turn generates a peptide called angiotensin which acts to constrict blood vessels, thereby causing the same effect as the sympathetic nervous system, though on a long-term basis.

There is a relationship between stress and the presence of cholesterol (Rosenman & Friedman, 1974). This begins to result in arterial plaques that narrow the arteries and further increase blood pressure. The increased tendency of blood to coagulate under stress further reinforces this through the tendency of blood platelets to add to the arterial plaque. The plaque tends to damage the artery wall, which the body tries to repair, which tends to make the plaques even thicker.

Under conditions of extreme stress, the presence of too much Cortisol has the effect of suppressing the immune system, thereby making it much less effective. Several studies have shown close correlation between stress and immunity from disease (Cohen, Tyrell & Smith, 1991, Heninger, 1995). There is also some evidence to suggest that there is a link between stress and the suppression of natural killer-cells, the bodies protection mechanism against tumours. (Shavit et al. 1984).

The interaction of different types of stressors is complex. There are believed to be two major factors in the relationship between stress and immunity (Ader 1983). Chronicity - prolonged stress, seemingly without end. This can lead to the exhaustion of the adrenal hormones, impaired immune response and exhaustion. Intensity is the power or strength of the stressor. It is believed that acute stressors imposed on a background of high, chronic stress are the worst combination (Heininger, 1995). Herbert and Cohen (1993) concluded that: 1) Objective stress events produce larger immune responses than self-reported stress. 2) The immune response varies with the duration of the stressor, with acute stressors generally increasing immunocompetence and chronic stressors generally impairing immunocompetence. 3) Interpersonal stressors result in different immune outcomes than non-social events. Although there is some conflicting evidence, it appears that interpersonal stressors, especially those that are chronic, produce a greater negative change in immune function than non-social stressors.

A third area of impact of stress is on the digestive system. There is clear evidence that stress leads to ulcers.