Relaxation may be defined as a positively perceived state or response in which a person feels relief of tension or strain. Meditation is one of the methods of relaxation. Both relaxation and meditation have a mental as well as physical dimension. They are believed not only to have beneficial effects on the mind, but also on the body itself. Meditation may be used as a treatment to help relieve stress in conditions such as coronary artery (heart) disease, essential hypertension, tension headache, insomnia, asthma, immune deficiency, panic and many others. Are these benefits a mere speculation or is there any proof to these claims ?
Our body responds to stress and relaxation through the three systems which are:
- the autonomic nervous system
- the endocrine system, and
- the skeletal (voluntary) and smooth (autonomic) musculature systems.
1. The autonomic nervous system
This nervous system controls our body parts which function automatically to the body’s needs. It has two branches: the sympathetic which increases arousal when the body is under threat, and the parasympathetic which restores the body to a resting state. The effect of the sympathetic nervous system is collectively known as the “fight-flight response” which is characterised by an increase in heart rate, blood pressure, blood clotting time, blood flow to voluntary muscles, blood glucose level, breathing rate, acuity of senses, sweating, and a decrease of the activity in the digestive tract, which are required for an alert or emergency.
In the absence of challenge or excitement, these actions are reversed and the parasympathetic system takes control. It also increases the tone in our small airways (bronchial constriction), promotes blood flow to the bowels and digestion is improved.
2. The endocrine system
The endocrine system works closely with the autonomic system by releasing hormones which modify the action of the internal organs in response to the environmental stimuli. The main organ of this system is the adrenal glands which are situated above the kidneys. They produce catecholamine hormones, noradrenaline and adrenaline. Noradrenaline is thought to produce changes associated with aggression, fighting behaviour, alertness and creates a feeling of arousal. Adrenaline is associated with anxiety and flight (flee) behaviour. Apart from these hormones, the adrenal glands also produce glucocorticoids, especially cortisol whose function is to maintain the fuel supply to the muscles. It also promotes the actions of the autonomic nervous system and regulates the immune system. Apart from sex hormones, most of the other hormones are produced in the brain. Among the hormones that are produced in the brain opiod peptides which include enkephalins, endorphins and dynorphins are of particular interest regarding the effects of meditation. They are considered to be associated with changes in the mood, pain threshold, immune activity and on bronchial (lungs) and arterial smooth muscle tone. Beta endorphins are produced in the hypothalamus of the brain and their levels are increased in regular exercise, meditation, and in acupuncture.
3. The skeletal and smooth musculature system
The muscles connected to the bones are voluntary and muscles in the internal organs are smooth muscles which are involuntary or autonomic. The release of tension in the skeletal musculature is thought to have a calming effect on the mind and exercise is helpful for relaxation.
Three types of psychological theory concerning relaxation through meditation have been proposed, namely: cognitive, behaviour, and cognitive-behaviour. This article will deal mainly with the effects of meditation on the body and will leave the effects on the mind temporarily.
Among many methods of meditation, awareness of breathing (Anapana) is the most popular technique. Other meditation methods will more or less, effect breathing at some stage and a slow, shallow breathing can change the autonomic system, the endocrine and the musculature systems.
Respiration is directly linked with the autonomic system which controls physiological arousal. Chemoreceptors in the walls of the aorta and the carotid arteries help to control breathing and are sensitive to changes in the amount of carbon dioxide circulating in the blood. The levels of carbon dioxide influence physiological activity, and are conventionally represented in terms of partial pressure of carbon dioxide (Pco2). Overbreathing leads to excessive loss of carbon dioxide and a lowered arterial Pco2 (hypocapnia), whilst underbreathing to a build up of Pco2 (hypercapnia). Mild hypercapnia is associated with lethargy and symptoms resembling those of parasympathetic dominance (relaxation). Further rises of Pco2 create an effect that mimics sympathetic dominance (fight-flight response).
A slow and shallow breathing in meditation can cause mild hypercapnia as Pco2 builds up with time. It also counteracts the effects of sympathetic activity by promoting the action of the parasympathetic nervous system. These changes results in a state of relaxation with a decrease in heart rate, blood pressure, blood coagulation time and acuity of senses. However, the activity of parasympathetic system may cause broncho-constriction and may also stimulate gastric acid secretion. These effects can aggravate asthma and gastric ulcer which is in contrast to the belief of the positive effect of meditation in these diseases.
This contradictory interpretation may be explained by the following mechanisms. Relaxation will reduce the blood level of noradrenaline, adrenaline and cortisol, and promotes the secretion of endorphins and other opoid (opium like) neuropeptides in the brain cells of hypothalamus. Lower levels of noradrenaline, adrenaline and cortisol can be beneficial to gastric ulcers (stress can aggravate gastric ulcers) and higher levels of opoid neuropeptides can modulate pain threshold, immune activity and on the bronchial smooth muscle tone.
It has been known for centuries that morphine abolishes tissue damage type pain, but not pin prick sensation or neurogenic pain. In the early 1970s, several research groups discovered that certain neurons (nerve cells) have morphine receptors or binding sites. These are called pharmacological receptors which are separate from physiological peripheral receptors, which transduce external energy (stimulus) into nerve impulses. Morphine is not a naturally occurring transmitter substance, but it imitates naturally occurring transmitters, enkephalins discovered in 1975, and other opiod substances, endorphins and dynorphin were discovered later. Morphine binding sites are not only found in some (but not all) neurons in pain pathways, but also in some neurons in the respiratory and vomiting centres of the brain.
Thus opioid neuropeptides can modulate pain threshold and respiration.
Proofs of the Concept
(I) Cortisol, ACTH and Beta-Endorphin levels
A study in 18 healthy volunteers who regularly practise Transcendental Meditation (TM) and in 9 healthy non-meditator Controls (C) found out that there was a significant diurnal rhythm of these hormones in the normal subjects (C). The levels were high in the morning (9am) and low in the evenings (8pm) reflecting to the state of relaxation of the subjects. Whereas, in the meditation group (TM) it was found that there was no diurnal change in the adreno-cortical stimulating hormone (ACTH, hormone produced from the pituitary glands in the brain for feedback control of producing cortisol ) and beta-endorphin levels, but the diurnal rhythm was present for cortisol hormone. The study reported that practitioners of TM with similar anxiety levels to those of control group (C) showed a different pattern in the daytime secretion of pituitary hormones. They concluded that TM thus appeared to have a significant effect on the neuroendocrine axis which they considered that it was due to a change in feedback sensitivity caused by the meditation practice.
Studies in animals suggest that chronic stress causes a high baseline level of cortisol and a low response to acute stress conditions and that such changes may contribute to disease. A study in humans who were exposed to experimental stressful conditions for 4 months found that the group who practised Transcendental Meditation (TM) had a low baseline level of cortisol and the response to stress conditions was significantly high. Whilst in the Control group of non practitioners the finding was reverse; the response of cortisol levels to stress conditions was lower than the basal cortisol level which was similar to that of the finding in animal studies. Other hormones (growth hormone, thyroid stimulating hormone & testosterone) were also measured and it was found that the baseline testosterone level was higher in TM than in the Control group which indicated that less chronic stress was present in TM. The study group concluded that the results appeared to support previous findings suggesting that repeated practise of TM reversed the effects of chronic stress significant for health.
Pressure pain threshold can be estimated in patients with tension headache by measuring the levels of beta-endorphin, substance P and serotonin in the blood. A study on 30 patients with tension-type headache (Test) was measured for the pressure pain threshold and compared with that of 30 age matched healthy subjects (Control). They found that the pressure pain threshold was significantly lower in the Test than in the Control. In the Test the levels of beta-endorphin and substance P were found to be lower, whilst serotonin level was higher than in the Control.
In Immune Activity
Our body has two defence systems to protect ourselves from the invasion of foreign substances including infectious organisms, namely: external defences which are skin and mucous membrane that act as a barrier to protect invasion from outside and inside; internal defences which constitute of cellular and biochemical agents collectively known as the immune system. In the cellular defence, macrophages play a very important role as they can detect and destroy the invaders and unwanted cells by engulfing, killing and dissolving them. They are important for acquired (specific or adaptive) immunity. Another type of cell, the natural (NK) cells often referred to as large granular lymphocytes are part of the early response to virus infection. The NK cells have low specificity and rapid action in destroying the invaders and are important in natural immunity.
In a laboratory study it was found that enkephalin stimulated natural killer cell activity. Opioid peptides were not found to effect the cytotoxic activity of macrophages. A study in laboratory mice that were injected intraperitoneally with enkephalin, beta endorphin and dynorphin or proenkephalin were found to increase natural killer cell activity in spleens, as well as an increase in the percentage of cells with killer cell phenotype.
Animal studies also reported that beta endorphins could influence bronchial smooth muscle tone. A study in 32 asthmatic patients (Test) and 12 healthy subjects (Control) found that there was a significant increase in beta endorphins in the baseline blood samples of asthmatics than in the Control, but after they were experimentally challenged with histamine to produce asthma the levels fall in the Test.
(II) Cardio Vascular changes
A study in 21 patients who had documented coronary artery (heart) disease found out that transcendental meditation (TM) had significant improvement (14.7%) in the exercise tolerance test, 11.7% increase in maximal workload, and significant improvement in ECG (18% delay in onset of ST-segment depression) after 8 months of practice.
Another study in elderly subjects indicated that 18 subjects who practised TM had a lower (15%) blood level of lipid peroxides responsible for hardening of blood vessels (atherosclerosis) and other chronic diseases associated with ageing, than in 23 subjects who did not practice TM. The finding was still significant when the dietary factor (red meat consumption) was adjusted.
Cardiovascular responses to stress reactivity has been proposed as a risk factor for hypertension. A study in 39 healthy males with normal blood pressure who were pretested for ambulatory (lying) blood pressure (BP) and cardiovascular reactivity to experimental stress were randomised to two groups to see if transcendental meditation (TM) was more efficient than a cognitive based stress education control (SEC). After 4 months of experimental stress they found that there was a significant reduction of 9mm Hg blood pressure in the TM compared to the SEC, although there was no change in the cardiovascular response to stressors. It was concluded that TM might be effective in the primary prevention of cardiovascular diseases in normotensive subjects.
Another study in 127 older African Americans hypertensives (90 to 104 mm Hg diastolic) who were categorised for hypertension risk (psychosocial stress, obesity, alcohol use, physical inactivity, dietary sodium-potassium ratio, and a composite measure) were randomised into two groups to compare between two stress reduction programmes; transcendental meditation (TM) and progressive muscle relaxation (PMR). It was found that both systolic and diastolic pressures changed from baseline to 3 months follow up for both sexes and for high and low hypertension risk level. They found that in the TM the adjusted declines were 10-12 mmHg for systolic and 6-8 mm Hg for diastolic pressures in women and men respectively. It was not found to be significantly different between the baseline and follow up BP in the PMR, especially in women.
These studies have provided evidence to support that transcendental meditation can release stress and has definite positive effects on hypertension and heart disease, and that beta endorphin and other opiod neuropeptides are increased by the technique. They do not however, provide evidence that meditation improves either asthma or immune activity although the opiod peptides are shown to be associated with these conditions. Meditation may improve tension headache and natural immunity (to virus infections) as provided by the indirect evidence from the studies.