Non communicable disease - parasympathetic activity - sympathetic activity - yoga
Introduction
It is said that yoga practice will reduce the risk of noncommunicable diseases (NCDs)
including heart disease, diabetes, neurological disorder, and respiratory diseases.
The significance of yoga in health and disease is so extensive and of such a general
nature that it has become a necessity for doctors who will be practicing in the 21st century.[1] A wide variety of common diseases such as coronary heart disease, hypertension,
and diabetes mellitus (DM) are now being documented to a faulty lifestyle. Yoga is
probably the best lifestyle ever devised in the history of humanity.[1] It is a simple, devoted, compassionate way and view of life, upon which people across
cultures and across countries have stumbled for time to time for centuries. Yoga is
finding an increasing approval as a nonpharmacological intervention for the prevention
and treatment of diseases.[1] Therefore, all the doctors should be well informed about yoga and how it impacts
human body system so that doctors may provide sensible answers to patients about the
fundamentals of yoga and its impact on health and diseases.[2]
[3] A consultant with a yogic attitude is more likely to transmit to the patient a positive
attitude and tranquil substantiation. A positive attitude and a peaceful mind are
conductive to healing and happiness, whatever may be the nature of disease or illness.[4]
“Yoga can be adept everywhere by people of all age groups, irrespective of their socioeconomic
status. It fits in very well with the healthy lifestyle that the WHO has been strongly
advocating for throughout the life cycle – from childhood to healthy aging. The United
Nation's pronouncement to observe June 21 as the International Yoga Day is a gratitude
of this ancient Indian practice which has become global. The Yoga Day will rightly
put the spotlight on physical exercise, much needed in today's world when sedentary
lifestyle is becoming a leading cause of illness.” Emphasizing that the Indian subcontinent
had a long history and rich tradition in conventional medicines and practices that
contribute to health and wellness of the people, we can say that yoga was one of the
finest traditional therapeutic systems in the ancient India.[5]
“Yoga is believed to offer means for the actualization of human potential to perfection
through its three-dimensional approach to health – physical, mental, and spiritual.
Yoga is very much relevant even today – as it is both a physical activity and an effective
way of managing stress,” and the world is fortunate that such conventional medical
practices have survive over the centuries.[5] Till few years back, yoga was considered an adjunct therapy in modern medicine.
However, during the last decade, yoga has got incorporated in modern medicine.[5] The diseases of modern civilization such as obesity, hypertension, DM, and coronary
artery disease are rooted due to faulty lifestyle. This is a stimulus to search for
a healthy lifestyle. Yoga is one of the best lifestyles ever devised by human beings.[6] Psychological stress has a major impact on the diseases related to modern civilization.
This is another stimulus to search for strategies for overcoming stress.[6] Yoga provides a new way of looking at life. Stress, anger, hostility, relaxation,
peace, love, emotion, and intimacy are difficult to measure, but it provides a solid
scientific foundation of mind–body relationship and emergence of psychoneuroimmunology.[7] All these cannot be measured, but their effect on body system can be quantified
by measuring certain biomarkers such as cytokine levels or measurement of natural
killer cells. Science demands quantifiable evidence. Providing evidence for the effects
of emotions on biological features may prove to be a great relevance to the health
and disease.[8] The evidence generated has made modern medicine accept the love, peace, joy, positive
thinking, relaxation, hope, etc., as therapeutic tools.[9] This is how yoga becomes a potent instrument for influencing the mind positively.[9] Based on the above traditional as well as scientific thinking, below are some of
the NCDs, for which yoga may be used with a favorable effect in modern medicine.
Yoga in Obesity and Cardiovascular Disease
Yoga in Obesity and Cardiovascular Disease
Obesity is a state of mild or low-grade inflammation,[10] which may later culminate in a chronic disorder if remains untreated. A number of
inflammatory mediators have been shown to be released by adipose tissue, which acts
as an endocrine organ with autocrine regulation.[11] Several studies suggest that inflammation contributes to the causation and progression
of cardiovascular disease (CVD).[12]
[13] Further, inflammatory mediators may trigger rupture of the atherosclerotic plaque
which may result in coronary thrombosis and ischemia [Figure 1].[14] In spite of the considerable improvement in therapeutic modalities in CVD, an effective
treatment leftover a challenge. The treatment modalities for weight reduction in the
management of patients with CVD and those at an augmented risk are paying attention
on nutritional interventions, increased physical activity, and pharmacological management.[15]
[16] It has been stressed that weight reduction is the main contributor for the correction
of deranged lipid profile,[17] especially by reduction in abdominal fat.[18] Recent studies have shown that lifestyle intervention is a promising option in patients
with CVD as well as those at an increased risk of CVD.[19] Therefore, lifestyle modifications aiming at weight reduction by physical activity,
dietary changes, yogic exercises including breathing exercises, and stress relaxation
have a very specific role in the management as well as in the prevention of cardiac
diseases.[20] Yoga combines a healthy lifestyle with mental peace, and a modification in lifestyle
and calming practices is shown to improve the clinical profile of patients with various
pathologies.[8]
[9] Routine practice of breathing exercise and meditation in healthy individuals led
to an improved cardiovascular metabolic status [Figure 1],[21]
[22] even by a short-term yoga-based routine intervention.[23] Notably, even short-term yoga-based broad lifestyle intervention led to a remarkable
reduction in blood pressure (BP), body mass index, and blood glucose with a clinically
significant improvement in lipid profile.[24] A similar reduction in weight was observed in another study that included an 8-week
of yoga training that resulted in an improvement in body composition and total cholesterol
levels in obese adolescent boys.[25] Long-term changes in lifestyle involving yogic exercises, stress reduction techniques,
and fat-free vegetarian diet led to angiographically demonstrable reduction in coronary
stenosis.[26]
[27] Another study showed that Surya namaskar (a yoga posture) resulted in an improved
cardio-respiratory fitness.[28] Similarly, a yoga-based lifestyle intervention resulted in a reduction in all lipid
profile parameters except high-density lipoprotein. The effect started from 4 weeks
and lasted for 14 weeks.[29] All these results indicate that a yogic lifestyle interference may have an effect
on some adaptable risk factors, which could make clear the protective and therapeutic
valuable impact of yoga in CVD. Overall, lifestyle intervention can transform the
evolution of the CVD.
Figure 1 Schematic diagram showing physiological basis of stress and stress-related disorders
due to abnormal psycho-neuro-immuno-endocrine system, HPA: Hypothalamic-pituitary-adrenal
axis
Diabetes Mellitus
Abnormal increase in sympathetic activity and reduction in parasympathetic activity
have been associated with Type 2 DM. Chronic stress, anxiety, and depression have
already been implicated in pathogenesis as well as the aftermath of diabetes. Some
studies have shown positive effects of yoga intervention on stress and anxiety.[30] Studies and reviews have clearly shown the positive effects of yoga on glycemic
control, BP, lipid profile, stress, anxiety, and depression, but have not identified
the mechanisms of the action of yoga in Type 2 DM. Previous studies have clearly stated
the need to review mechanisms by which yoga helps in diabetes.[31]
Yoga practice is directly related to improved insulin sensitivity to glucose signals
in Type 2 DM. It attenuates the negative relationship between factors causing insulin
resistance such as obesity, increased waist circumference, and dyslipidemia.[32] Yoga also improves the sensitivity of beta cells of pancreas to glucose signals.
Manjunatha et al. have stated that there is reduction in the brisk release of insulin when glucose
level tends to fall whereas there is an increased insulin release when glucose tends
to rise in blood.[33] This mechanism gets support from a previous study of Sahay who observed a fall in
fasting insulin level when glucose level is at a minimum level. Yoga optimizes insulin
secretion as per bodily requirement through its neuro-endocrinal effects and thereby
bringing about normalcy in the insulin/glucose ratio, which is suggestive of better
peripheral utilization of insulin and reduced insulin resistance.[34]
Yoga has been widely recommended for diabetes. A study by Sahay et al. deliberately dissected yoga into small components and studied each separately.[35] Among the alternatives which reduced fasting and postprandial blood glucose were
Pranayama, Dhanurasana + Ardha Matsyendrasana, Halasana + Vajrasana, and Naukasana
+ Bhujangasana. Further analysis revealed that Dhanurasana was the most effective
asana for diabetes. A combination of mudra and salabhasana was ineffective, and produced
a nonsignificant rise in fasting blood glucose in their study on five participants.
This small number of participants and statistically nonsignificant rise in blood glucose
make such a conclusion unwarranted.[35]
It is not easy to recognize any lone physiologic mechanism of action of yoga in Type
2 DM as the risk factors and etiologies of Type 2 DM are multi-factorial. Similarly,
it is not easy to hypothesize any single unidirectional conduit of yoga action in
Type 2 DM. Yoga's mechanisms of action in Type 2 DM are integrated and their effect
is multi-systemic. The psycho-neuro-endocrine and immune mechanisms of the action
of yoga in Type 2 DM symbolize a possible approach to accepting its holistic effects
on disease modulation of Type 2 DM. This review suggests psycho-neuro-endocrine and
immune mechanisms that may be imperative to perceptive yoga's actions on Type 2 DM
[Figure 2] and [Figure 3].
Figure 2 Model for obesity, inflammation, and vascular endothelial changes. ER: Endoplasmic
reticulum; NFκβ: Nuclear factor kappa beta; IL-6: Interleukin-6; CRP: C-receptive
protein; PAI-1: Plasminogen activator inhibitor-1; TNF-α: Tumor necrosis factor-alpha;
FFA: Free fatty acids; SMC: Smooth muscle cells; UPR: Unfolded protein response
Figure 3 Mechanism of action of yoga through parasympathetic activation and associated anti-stress
mechanisms. It reduces perceived stress and hypothalamic-pituitary-adrenal axis activation,
thereby improving overall metabolic and psychological profiles, increasing insulin
sensitivity, and improving glucose tolerance and lipid metabolism. HPA: Hypothalamic-pituitary-adrenal
axis; HR: Heart rate; BP: Blood pressure
Yoga and Hypertension
Meditation has been shown to reduce systolic BP and diastolic BP of hypertensive patients
in several studies. The mechanism underlying the BP-lowering effect is complicated.[36]
[37]
[38] One theory suggests that imbalance in autonomic performance plays a key role in
the origin of hypertension[39]
[40]
[41] comparatively over activity of the sympathetic nervous system which ultimately desensitizes
cardiopulmonary and arterial baroreceptor reflex and chemoreceptor reflex, leading
to a resetting of threshold BP values at which regulatory signals are triggered.[42] Controlled breathing with prolonged breath cycles may positively alter, i.e., reduces
chemoreceptor sensitivity, thereby reducing arterial baroreceptor lethargy and sympathetic
outflow.[43] Other potential mechanisms involve the fact that amplification of tidal volume activates
the Hering–Breuer reflex mediated by pulmonary stretch receptors.[44] This reduces the chemoreflex sensitivity, in turn upregulating baroreflex receptor
sensitivity and thereby decreasing arterial BP. It has also been suggested that controlled
slow breathing entrains central nervous system nuclei, in which respiratory and cardiovascular
system centers cross, thus positively alters the regular sympathetic outflow to the
vasculature.[54] Some other studies suggest that the decrease in BP occurs mainly via a decrease
in systemic vascular resistance and total arterial compliance.[45]
[46]
[47] However, the overall biological mechanism and the integrated neural pathways involved
in lowering BP by slow deep breathing have yet to be completely elucidated.
Physiological Basis of Blood Pressure Lowering by Breathing Exercise
Physiological Basis of Blood Pressure Lowering by Breathing Exercise
The mechanism whereby meditation techniques lower BP when it occurs remains unclear.
It has been suggested that the mechanisms may lead to reductions in stress and physiological
arousal, thereby producing favorable effects on the autonomic nervous system balance[48]
[49] [Figure 1]. It has been speculated that relaxation techniques may favorably alter autonomic
nervous system balance and/or the hypothalamic-pituitary-adrenal (HPA) axis.[50] The precise pathways responsible when relaxation therapies produce a decrease in
BP require clarification.
Controlled Breathing
Meditation, yoga, and music decrease sympathetic nervous system activity, sensitize
arterial and cardiopulmonary baroreceptors, and in so decrease BP lability and increase
resting BP. Similarly, slow breathing (<8–10 breath per minute), especially with prolonged
expiration, reduced sympathetic nerve activity while increasing parasympathetic activity
and reducing BP [Figure 1].[51]
[52] The systems require two 12–15 min sessions daily, endeavoring to achieve at least
45 min of slow breathing time per week. While there are no known contraindications,
this technique requires a fair amount of discipline. The suitable candidates for this
therapy might include the prehypertensive or mildly hypertensives, with small BP reductions
required; white coat hypertensives where behavioral feedback may minimize the alerting
reaction; as a last resort in patients with resistant hypertension and/or those with
multiple medication sensitivities/intolerances; and in patients who seek a greater
degree of empowerment in managing their hypertension, but still, more persuasive evidence
is needed before device-guided breathing can be more generally recommended for BP
reduction.[53]
Orthopedic Problems
Yogasans have been used for orthopedic problems such as cervical spondylosis and backache,
which would benefit from strengthening of specific groups of muscles and also from
the improvement of posture.[50] Asans for relaxation have been used for conditions requiring relief from muscle
spasm. The favorable effects of yoga in orthopedic problems are not difficult to explain.
Asans which strengthen back muscles understandably relieve a backache. Increase in
flexibility and decrease in body weight resulting from the asans ameliorate pain not
only in the knee joint but also in the other joints.
Physiological Basis of Action of Yoga in Noncommunicable Diseases
Physiological Basis of Action of Yoga in Noncommunicable Diseases
We know yoga works, but we do not know how it works. The mind–body relationship is
now widely accepted and there is considerable evidence supporting it.[55]
It has shown in one study that a set of selected asans return this sensitivity towards
normal. Associated with the return of baroreflex sensitivity is a fall in blood pressure
towards normal.[56] Stress reduction and the favorable effect of positive emotion on the immune response
possibly contribute to the beneficial effect effects of yoga in bronchial asthma patients[55] [Figure 1]. Yogic exercise also benefits asthma by improving pulmonary performance, loss of
weight, and physical exercise also improves glucose tolerance, which in turn helps
DM. Some dietary modifications add stress reduction, frequently associated with yoga,
which may contribute to improvement in glucose tolerance. The same mechanism contributes
to the favorable impact on coronary heart disease.[56] According to the theory proposed by Streeter et al., the decreased parasympathetic nervous system and GABAergic activity that underlie
stress-related disorders can be corrected by yoga practices resulting in the amelioration
of disease symptoms. Heart rate variability testing has a great role to play in our
understanding of intrinsic mechanisms behind such potential effects of yoga. Innes
et al. had earlier also postulated interconnected pathways by which yoga reduces the risk
of CVDs through the mechanisms of parasympathetic activation coupled with decreased
reactivity of sympathoadrenal system and HPA axis[56] [Figure 1].
Therefore a shift in autonomic balance toward parasympathetic dominance may explain
the decrease in heart rate, fall in BP, and improvement in gastrointestinal function.
The increased glucocorticoid secretion in response to an acute stress may explain
the better ability to handle the stress. The physical exercise, dietary modification,
and stress reduction associated with yogic practices may explain the fall in plasma
glucose and improved lipid profile.
Future Prospect and Implication of Yoga
Future Prospect and Implication of Yoga
It is now well recognized that stress weakens our immune system. Scientific research
in several recent studies has shown that the physiological, psychological, and biochemical
impact of yoga are of anti-stress in nature. Mechanisms hypothesized and postulated
are the re-establishment of autonomic function balance as well as a progress in healing,
regenerative and curative capacity of the individuals.
The main aims of the therapeutic implications of yoga should be to increase parasympathetic
and decrease sympathetic activities. It may be further hypothesized that yoga-based
practices correct under-activity of the parasympathetic nervous system and gamma-amino
butyric acid systems, partly through the stimulation of the vagus nerves, the main
peripheral pathway of the parasympathetic nervous system.
This enables us to move from a state of ill health and sickness to the one of fitness
and well-being that eventually allows us to move from the lower animal nature to the
higher human nature and finally the highest divine nature.
The need of the current time is to have an integrated approach toward complete therapy
and to utilize yoga therapy in harmonization, cooperation, and collaboration with
other systems of medicine such as modern medicine, Ayurveda, and naturopathy. Advice
on diet and lifestyle is very important, irrespective of the mode of therapy that
is employed for a particular patient.
Financial support and sponsorship
Nil.
