Written by: Roberta Kline, MD
Stress is part of life, and comes in many forms including physical, emotional, mental and environmental. Foods we eat, unhealthy relationships, difficulties at work, toxins in our environment, even poor posture or lack of sunshine can all create stress on our bodies. But when stress is catastrophic or becomes chronic, it creates imbalances in this functioning that are much more likely to promote disease while at the same time preventing healing from taking place. [1]
With people under record levels of chronic stress, it is no wonder we have an epidemic of people suffering from all sorts of health issues and chronic diseases. Heart disease, diabetes, obesity, pain, anxiety, depression, infertility, cancer, autoimmune diseases such as arthritis, neurodegenerative diseases such as Alzheimer’s …. These are just some of the many health conditions that have been linked to diet and lifestyle including chronic stress. [2, 3]
But how does this work? And is meditation the answer to reversing this trend? Science is revealing some interesting clues.
One big connection is our nervous system. Our nervous system is our superconductor network of information exchange throughout our bodies, and consists of two main parts. The first is the central nervous system (CNS). As it sounds, it’s our command center where all data comes to be processed, and is made up of the brain, spinal cord, and nerves. The second is called the peripheral nervous system (PNS) and it connects every part of our body to our CNS through individual nerve cells called neurons and clusters of neurons known as ganglia.
The PNS is further divided into the Somatic Nervous System, also known as the voluntary nervous system, and the Autonomic Nervous System. The Autonomic Nervous System (ANS) manages all bodily functions that are not under conscious control. This includes heart rate, blood pressure, digestion, respiration, cellular activity, immune system, hormones, brain function, sexual function, and even body temperature.
The ANS is further divided into two parts: the Sympathetic Nervous System (SNS), which regulates our “fight or flight” response, and the Parasympathetic Nervous System (PNS), which controls our “rest and digest” response. They work closely together in a complex dance, maintaining our bodily functions and ensuring our survival every second of our lives.
Many health issues, including most chronic diseases such as heart disease, autoimmune disease, diabetes, depression and anxiety, and cancer, are related to an imbalance of our autonomic nervous system. Most typically, it is too much of the “fight or flight” and not enough of the “rest and digest” that leads us into this imbalance. [4]
The Sympathetic Nervous System is located in the CNS, and in the spinal nerves from T1 (the thoracic region) down to L3 (the lumbar region) out to the neurons in the regions of the body supplied by these nerves. This sympathetic response is designed to keep us safe in the face of immediate danger. It signals the brain to turn up the volume on any physiological function crucial to staying to fight or running away from the source of the danger. Catecholamines such as epinephrine (adrenaline), norepinephrine (noradrenaline) and dopamine are released and a cascade of events happens rapidly – before we are even consciously aware that there is a threat. These include:
• Blood flow diverted to the heart, lungs and skeletal muscle
• Increased heart rate, blood pressure and respiratory rate
• Enlargement of bronchioles (in lungs)
• Dilation of pupils
• Rapid conversion of glycogen to glucose for fuel
• Activation of immune system
All other functions, including digestion, urination, higher level thinking, even sexual function and cellular repair, are temporarily turned off, so that all of our energy and resources go only toward ensuring our immediate survival. If the threat goes on for a longer period of time, a secondary system called the HPA (Hypothalamic – Pituitary – Adrenal) Axis takes over and relies on elevated cortisol and other hormonal changes to continue the high alert state.
But our bodies are not designed to be in this activated high-alert state for long periods of time. Once the immediate threat is gone, we are supposed to go back to our normal state of relaxation. This is the job of the Parasympathetic Nervous System.
REST AND DIGEST
The Parasympathetic Nervous System (PSNS) is located in the brain stem, includes nerves to the eyes and face, vagus and 10th cranial nerves, and sacral nerves (S2-S4). Regulated in large part by the vagus nerve (75%), it impacts a vast array of crucial bodily functions. When the parasympathetic response is triggered, it counteracts the fight or flight response primarily through release of acetylcholine.Parasympathetic activation results in production of tears, saliva, and constriction of the pupils; lower and more variable heart rate, lower blood pressure and respiratory rate. It enables creative and critical thinking, normal kidney function and urination, improves immune function, enables sleep, sexual arousal and replenishment of fuel stores in organs; plus everything involved in digesting and utilizing our food including elimination and insulin production. Even mood and social bonding and connection are linked.
Healing requires coordination of a complex array of biological functional and systems. Research is rapidly expanding our understanding of the importance of the parasympathetic response, and how meditation helps to restore balance. While this impacts every biological system, here are some key areas:
Digestion
Nutrients must be properly digested to extract them from our food and into our cells, where they are critical to every function our bodies must carry out. From vitamins and minerals that are needed in every biochemical reaction, to energy production in our mitochondria, to building blocks of our proteins that form our enzymes, neurotransmitters, hormones, even our DNA - all of our cells need these basic materials to function. Stress shuts down our digestion, and if it goes on long enough our cells become depleted of the very nutrients needed to function and repair.
Approximately 90% of our immune system resides in our gastrointestinal tract. While it is needed to defend us against invaders such as bacteria and viruses, it can also go awry if unchecked. This “runaway” inflammation is linked to most chronic diseases, and paradoxically also reduces the ability to respond to infections. Our immune system has other functions, including being a cleaning crew. It removes debris left over from battling invaders. It also removes our own dead or badly damaged cells, and signals new and healthy ones to replace them. Stress results in an imbalanced immune system, making us vulnerable to infections as well as chronic disease.
Mitochondria
These tiny structures exist within every cell in the body, and as the “power plants” of the cell they are responsible for producing all of the energy needed for every single function. This energy is produced as ATP and to make it requires key nutrients from food to be digested and absorbed from the gut. But producing this energy also creates toxic molecules, which are neutralized by antioxidants which also come from our diet. If the demand for energy is too great for too long, the mitochondria – and its cell – become damaged. Without healthy mitochondria, cells become damaged, dysfunctional and even die.
The brain normally utilizes about 20% of our energy supplies, primarily in the form of glucose or ketones. This requires good digestion and healthy mitochondria to keep the brain supplied with fuel to function.
Acetylcholine is a major neuro-transmitter in the brain and in nerve endings through the peripheral nervous system; it is also anti-inflammatory. It is made in the mitochondria using some of the same ingredients needed for ATP production.
Serotonin, a major neurotransmitter impacting mood, is mostly produced in the gut. When the stress response is prolonged, this depletes the brain’s capacity for creative and critical thinking and mood regulation, often further impairing the ability to deal with stress.
While meditation has been practiced in various forms for centuries, and has long been associated with many parameters of improved health and well-being, science is only recently starting to understand the mechanisms by which it works. Studies are demonstrating the positive impact of meditation practices on various disease conditions, and the potential power for it to change the trajectory of this epidemic of chronic disease. Research findings on HOW it works are not all consistent though, as ways of meditating can be quite varied and this seems to impact the results. However, some common threads are emerging; two main mechanisms are outlined below.
Default Mode Network
One mechanism by which meditation works is by altering connectivity in the brain – the so-called Default Mode Network, or DMN. This is a network of brain regions that is active when the brain is restful but awake. Meditation seems to decrease this DMN activity, leading to increased cortical connectivity [5] - in other words, there is activity connecting areas of the brain that aren’t normally part of this network that enables us to take a different, more detached perspective on things in our life. When we aren’t so attached to events, the sympathetic response is less likely to be triggered, or if it is triggered it is to a lower extent that is easier to recover from.
Meditation also activates the parasympathetic response, in large part through the vagal nerve. This not only impacts heart rate and other vascular parameters, it also connects our gastrointestinal tract to our brain. There is now a growing body of evidence that this bidirectional communication through the “brain-gut axis” is a complex system that is key to our health, and when it is out of balance is linked to many health issues. [6]
Meditation has been shown to increase vagal nerve activity, or tone, and restore normal functioning of these many systems including digestion, immune response, and brain neuroplasticity/resilience. [6] It is thought that one way this occurs is through deep breathing, although there may be other mechanisms in play. As we learn more about how meditation works and how it influences our biology, we can develop more targeted and personalized approaches to maximize its potential – while making it easy and accessible for people to integrate into their daily lives.
EPILOGUE
References:
(1) Furman D et al. Chronic inflammation in the etiology of disease across the life span. Nat Med 25, 1822–1832 (2019).
(2) Cohen S et al. Chronic stress, glucocorticoid receptor resistance, inflammation, and disease risk. PNAS April 2, 2012: 109 (16) 5995-5999
(3) Vancampfort D et al. Perceived Stress and Its Relationship With Chronic Medical Conditions and Multimorbidity Among 229,293 Community-Dwelling Adults in 44 Low- and Middle-Income Countries. American Journal of Epidemiology, Volume 186, Issue 8, 15 October 2017, Pages 979–989
(4) Agnese Mariotti. The effects of chronic stress on health: new insights into the molecular mechanisms of brain–body communication. Future Sci OA. 2015 Nov; 1(3): FSO23.
(5) Jerath et al Dynamic change of awareness during meditation techniques: neural and physiological correlates. Front. Hum. Neurosci., 17 September 2012 Sec. Cognitive Neuroscience
(6) Breit et al Vagus Nerve as Modulator of the Brain–Gut Axis in Psychiatric and Inflammatory Disorders. Front. Psychiatry, 13 March 2018
Additional Resources:
Jacob Tindle; Prasanna Tadi. Neuroanatomy, Parasympathetic Nervous System. StatPearls Publishing Jan 2022
The Neuroscience of Meditation. Understanding Individual Differences. Academic Press 2020
Disclaimer: MEDTECH REVIEWS* is a non-commercial user review of health-related technologies and is not intended as a marketing program for any device(s) featured in this video for evaluation. This presentation is for informational use only and does not offer any direct medical claims whatsoever. Statements from all speakers herein are expressing their own unscripted views that do not reflect those of our producers. Always seek the advice of your physician or other qualified health care provider with any questions you may have regarding a medical condition or treatment.
Copyright Notice: The materials provided on this website/web-based article are copyrighted and the intellectual property of the publishers/producers (The NY Cancer Resource Alliance/IntermediaWorx inc. and The AngioFoundation). It is provided publicly strictly for informational purposes within non-commercial use and not for purposes of resale, distribution, public display or performance. Unless otherwise indicated on this web based page, sharing, re-posting, re-publishing of this work is strictly prohibited without due permission from the publishers. Also, certain content may be licensed from third-parties. The licenses for some of this Content may contain additional terms. When such Content licenses contain additional terms, we will make these terms available to you on those pages (which his incorporated herein by reference).The publishers/producers of this site and its contents such as videos, graphics, text, and other materials published are not intended to be a substitute for professional medical advice, diagnosis, or treatment. For any questions you may have regarding a medical condition, please always seek the advice of your physician or a qualified health provider. Do not postpone or disregard any professional medical advice over something you may have seen or read on this website. If you think you may have a medical emergency, call your doctor or 9-1-1 immediately. This website does not support, endorse or recommend any specific products, tests, physicians, procedures, treatment opinions or other information that may be mentioned on this site. Referencing any content or information seen or published in this website or shared by other visitors of this website is solely at your own risk. The publishers/producers of this Internet web site reserves the right, at its sole discretion, to modify, disable access to, or discontinue, temporarily or permanently, all or any part of this Internet web site or any information contained thereon without liability or notice to you.
