By guest contributors Andrew McGonigle, MD & Matthew Huy, MSc, authors of The Physiology of Yoga
Introduction from Jenni
Welcome to part 2 of 2 of this educational series from two amazing special guest authors I invited to contribute to my blog! You can find the first article in their series here.
I’m thrilled to feature both of these science-based articles by Andrew McGonigle, MD and Matthew Huy, MSc here on my platform. Both authors are longtime yoga teachers who teach anatomy and physiology in yoga teacher trainings worldwide. Andrew is a medically-trained yoga teacher and educator, and Matt recently finished his master’s degree in Sport, Health & Exercise Science at Brunel University in London.
Andrew and Matt co-authored a new book, The Physiology of Yoga, that just released in June 2022 (published by Human Kinetics). I’m so excited about this new educational resource that’s now available for the yoga community!
This article here on my blog is adapted from Andrew and Matt’s new book. You can read more about their book (which I highly recommend!) below, after the conclusion of the article. And you can order your copy of The Physiology of Yoga right here!
One aspect I love about the book is the abundance of physiology and yoga myths and misconceptions that the authors thoughtfully and diplomatically question using insights from scientific research. In today’s article, we’ve selected three specific claims about yoga’s impact on physiology that we felt would be particularly relevant for my audience.
The three claims are as follows:
“Yoga boosts the immune system.”
“Heavy sweating during hot yoga detoxes the body.”
“Inversions bring more blood to the brain and stimulate the pineal gland.”
We hope you find the insights that Andrew and Matt have shared about these topics to be both interesting and educational. Enjoy reading, and please let us know what you think if you have a moment!
3 Claims About Yoga You Won’t Believe Aren’t True!
By Andrew McGonigle, MD & Matthew Huy, MSc
Claim #1: Yoga Can Boost the Immune System Over and Above Normal, Healthy Function
There are many claims about different lifestyle interventions, including yoga, enhancing our immune system, but the concept of boosting immunity makes little sense scientifically. In fact, boosting the number of immune cells in your body would not necessarily be a good thing. If your innate immune response was constantly stimulated, you would feel permanently unwell with a runny nose, fever, and lethargy. Inflammation is a defensive reaction against pathogens or irritants and is a crucial part of our immune process. Persistent inflammation has been linked to depression (Haapakoski et al., 2016).
Luckily there is no way to intentionally boost the innate immune system. For most of us, the body already produces many more lymphocytes (white blood cells) than it can possibly use, and the extra cells remove themselves through a natural process of cell death called apoptosis. Overall, our immune system already does a remarkable job of defending us against disease-causing microorganisms without needing to be further enhanced. Although some lifestyle interventions have been found to alter some immune system components, currently there is no evidence that they boost immunity to the point where the person is better protected against infection and disease.
It is widely accepted that moderate exercise is good for us. Exercise can contribute to general good health and therefore to maintaining a healthy immune system. Exercise promotes good blood circulation, which also helps the immune system to work optimally, and is one of the most widely studied behavioral interventions in terms of its immunomodulatory effects.
Studies demonstrate an association between physical inactivity and low-grade systemic inflammation in healthy subjects, while regular exercise protects against diseases associated with chronic low-grade systemic inflammation (Petersen and Pedersen, 2005). A study by Martin, Pence, and Woods (2009) suggested that moderate intensity exercise improves the immune response to respiratory viral infections. In a systematic review of the literature, Ploeger and colleagues (2009) investigated the effects of acute and chronic exercise on various inflammatory markers in patients with a chronic inflammatory disease. They reported that while training programs can reduce chronic inflammation in some patients, single bouts of exercise might elicit an aggravated inflammatory response. They suggested that the exercise training-induced response appears highly dependent on the type of disease; the severity of the disease; and the frequency, duration, and intensity of the exercise intervention. The authors also noted that the results of the review reveal a major gap in our knowledge regarding the evidence for safe but effective exercise for patients with a chronic inflammatory disease. A study by Haaland and colleagues (2008) also reported that the intensity of the exercise plays an important role. They suggested that strenuous exercise may cause acute immunologic changes (such as diminished natural killer cell activity), which may predispose to infection in certain individuals.
You’ve probably heard the phrase “An apple a day keeps the doctor away!” It is well known that a balanced diet plays an important role in helping our immune system to work optimally. But what about claims that certain multivitamins and supplements can boost our immune system? In a systematic review and meta-analysis of randomized controlled trials looking at the role of multivitamins and mineral supplements in preventing infections in elderly people, El-Kadiki and Sutton (2005) concluded that the evidence for routine use of multivitamin and mineral supplements to reduce infections was weak and conflicting. Only eight trials met their inclusion criteria, and owing to inconsistency in the outcomes reported, not all the trials could be included in each meta-analysis.
Much more good quality research is needed to give us a better understanding of the role that multivitamins and supplements play here. If you already have a balanced diet that meets the recommended amounts of nutrients, there is probably no need to take vitamin and mineral supplements to enhance your immune system. If you are undernourished in some way, then taking specific supplements may help you to reach recommended nutritional levels.
While it is important to reaffirm that moderate exercise and a balanced diet are good for us, it is also important to reiterate that there are currently no scientifically proven direct links between lifestyle interventions and enhanced immune function.
Claim #2: Heavy Sweating During Hot Yoga Detoxes the Body
Detoxification is the physiological processes through which the body identifies, neutralizes, and eliminates toxic substances and metabolic byproducts. As mentioned in our previous blog post, detoxification is an essential part of homeostasis, and our bodies naturally possess the capacity to perform these processes very effectively. Without an effective detoxification system, we would be very unwell.
Sweat glands are often perceived to play an important excretory function, similar to that of the kidneys. However, in a comprehensive review, Baker (2019) concluded that the role of the sweat glands in eliminating waste products and toxicants from the body seems to be minor compared with other avenues of breakdown (liver) and excretion (kidneys and gastrointestinal tract). The results of studies suggesting a larger role of sweat glands in clearing waste products or toxicants from the body (e.g., concentrations in sweat greater than that of blood) may be due to issues with the method of the studies rather than evidence for selective transport. Nevertheless, studies have shown that perspiration plays a role in skin hydration and microbial defense (Schröder and Harder, 2006; Watabe et al., 2013).
So it appears that heavy sweating in a hot yoga class or in a sauna might not help us to relinquish all those perceived toxins after all. However, the good news is that practicing yoga as part of a healthy lifestyle will allow our kidneys, liver, and gastrointestinal tracts to work optimally.
Claim #3: Inversions Bring More Blood to the Brain and Stimulate the Pineal Gland
There is widespread belief that inverting the body during asanas such as Headstand has many potential benefits including increasing blood flow to the brain and stimulating the pineal gland. But can these claims be backed up with science?
Importantly, blood flow to the brain is relatively constant despite changes occurring elsewhere in the body. In healthy adults, large changes in blood pressure result in little or no change in cerebral blood flow (Paulson, Strandgaard, and Edvinsson, 1990). This mechanism of autoregulation of cerebral blood flow is vital since the brain is very sensitive to too much or too little blood flow. Only in severe head injury or acute ischemic stroke do we lose this autoregulation, leaving surviving brain tissue unprotected against the potentially harmful effect of blood pressure changes. So it is reassuring to know that whether you regularly invert your body or not, your brain is receiving just the right amount of blood supply to meet its demands.
The pineal gland has been referred to as the third eye because of its location in the geometric center of our brain. The French philosopher, mathematician, and scientist Descartes regarded the pineal gland as the principal seat of the soul and the place in which all thoughts are formed. It is roughly the size of a soybean and is considered a somewhat mysterious organ because it was the last of the endocrine glands to have its function understood and described.
In addition to producing melatonin, the pineal gland also produces extremely tiny amounts of N,N-dimethyltryptamine (DMT), a potent psychedelic. While it has been proposed that the pineal gland secretes large quantities of DMT during extremely stressful life episodes, notably in the event of birth and death, to produce out of body experiences, there is a lack of evidence to back up this claim (Nichols 2018). This gland has the highest calcification rate among all organs and tissues of the human body. Pineal calcification is thought to jeopardize the amount of melatonin that can be produced by the gland and may be associated with a variety of neuronal diseases (Tan et al., 2018). There is, however, no research on the effect that yoga can have on the pineal gland. Maybe one day we will discover that Headstands decalcify the pineal gland, but until then just enjoy the literal change in perspective.
One physiological process that inverting the body can help with is venous return. Blood is easily pumped to our lower limbs from the heart via large arteries; however, returning blood to the heart is not such an easy process. The walls of the veins are considerably thinner, and their hollow passageways (lumens) are correspondingly larger in diameter compared to arteries, allowing more blood to flow with less vessel resistance. But by the time blood has passed through capillaries and entered venules and then veins, the pressure initially exerted on it by heart contractions has diminished significantly. While arteries can constrict quite dramatically, veins really only stiffen. The venous system is also normally working against gravity to return blood from the lower limbs to the heart. Inverting the body causes a transient increase in venous return (Haennel et al., 1988). Therefore, incorporating yoga asanas such as Supported Bridge Pose (Setu Bandha Sarvangasana) or Legs-Up-the-Wall (Viparita Karani) into a yoga practice can have an impact on venous return.
These three claims are tempting to believe on the surface. But as we can see, physiology is incredibly complex with many factors including activity level, stress, hormones, age, biological sex, and genetics – among countless others – affecting our health.
Nonetheless, exercise (including yoga!), sleep, and a balanced diet are some of the best things we can do for overall health and recommend to others.
This article is adapted from the book The Physiology of Yoga by Andrew McGonigle and Matthew Huy, published by Human Kinetics in June 2022.
In this book, Andrew and Matt look at the anatomy and physiology of the systems of the body (from the musculoskeletal to the digestive and everything in between) and explore the latest research on how yoga affects these systems.
They examine topics such as whether yoga can reduce blood pressure, whether yoga can help treat diabetes, and whether breathwork improves mental health. They also examine whether some common claims heard in the yoga studio have any scientific basis.
Order your copy of The Physiology of Yoga here!
**Read Part 1 of this article series here!
About the Authors:
Andrew McGonigle, MD is a medically trained yoga anatomy teacher empowering yoga teachers to teach from a more science-informed perspective.
Website: www.doctor-yogi.com / Instagram: @doctoryogi
Matthew Huy, MSc is an American-born, UK-based senior yoga teacher who also teaches anatomy and physiology on several teacher training programmes in the UK and abroad. He holds a Master’s in Health & Exercise Science and is the co-author of The Physiology of Yoga, published in June 2022 by Human Kinetics.
Website: www.matthewhuy.com / Instagram: @yogawithmatt
El-Kadiki, A., and A. Sutton. 2005. “Role of Multivitamins and Mineral Supplements in Preventing Infections in Elderly People: Systematic Review and Meta-Analysis of Randomised Controlled Trials.” BMJ (Clinical Research ed.) 330 (7496): 871.
Haaland, D., T. Sabljic, D. Baribeau, I. Mukovozov, and L. Hart. 2008. “Is Regular Exercise a Friend or Foe of the Aging Immune System? A Systematic Review.” Clinical Journal of Sport Medicine 18:539-548.
Haapakoski, R., K.P. Ebmeier, H. Alenius, and M. Kivimäki. 2016. “Innate and Adaptive Immunity in the Development of Depression: An Update on Current Knowledge and Technological Advances.” Progress in Neuro-Psychopharmacology & Biological Psychiatry 66: 63-72.
Haennel, R., K. Teo, G. Snydmiller, H. Quinney, and C. Kappagoda. 1988. “Short-Term Cardiovascular Adaptations to Vertical Head-Down Suspension.” Archives of Physical Medicine and Rehabilitation 69 (5): 352-357.
Martin, S., B. Pence, and J. Woods. 2009. “Exercise and Respiratory Tract Viral Infections.” Exercise and Sport Sciences Reviews 37 (4): 157-164.
Nichols, D. 2018. “N,N-dimethyltryptamine and the Pineal Gland: Separating Fact From Myth.” Journal of Psychopharmacology 32 (1): 30-36.
Paulson, O., S. Strandgaard, and L. Edvinsson. 1990. “Cerebral Autoregulation.” Cerebrovascular and Brain Metabolism Reviews 2 (2): 161-192.
Petersen, A., and B. Pedersen. 2005. “The Anti-Inflammatory Effect of Exercise.” Journal of Applied Physiology 98:1154-1162.
Ploeger, H., T. Takken, M. de Greef, and B. Timmons. 2009. “The Effects of Acute and Chronic Exercise on Inflammatory Markers in Children and Adults with a Chronic Inflammatory Disease: A Systematic Review.” Exercise Immunology Review 15:6-41.
Tan, D., B. Xu, X. Zhou, and R. Reiter. 2018. “Pineal Calcification, Melatonin Production, Aging, Associated Health Consequences and Rejuvenation of the Pineal Gland.” Molecules 23 (2): 301.