Yoga is a timeless and pragmatic science that evolved over thousands of years in India. It deals with the physical, mental, moral and spiritual well-being of human beings as a whole. The word yoga is itself derived from the Sanskrit word yuj, which means to join or attach. It also means union or communion, a true union of our will with the will of God. It is one of the means or techniques for transforming consciousness and attaining liberation (moksha) from karma and rebirth (samsara).
It is believed that yoga began in India in 3000 B.C. Stone seals with yoga poses dating to this era have been excavated at archeological sites in the Indus valley. It was Patanjali who first organized the practice of yoga in the Yoga Sutras around 300-200 B.C. He enumerates eight limbs or stages of yoga as a path to attain liberation. His practice is called the Ashtanga (eight limbs) yoga. Asanas (yogic poses) and pranayama (breathing techniques) include two of the eight limbs. Over the years, various forms/modifications of yoga have evolved, including Hatha, Vinyasa, Power, Bikram and Iyengar, to name a few.
Yoga was introduced to the United States only in the 19th Century, prominently by Swami Vivekanand at the World Parliament of Religions in Chicago in 1893. Yoga has gained increasing popularity in the United States with an increasing number of yogis and yogins every year. The 2016 Yoga in America Study Conducted by Yoga Journal and Yoga Alliance found that the number of Americans practicing yoga increased from 20.4 million in 2012 to more than 36 million in 2016. There was an increase in male practitioners in 2016 (10 million) and an increase in practitioners over age 50 (14 million) compared to 2012.
Yoga is revered for its health benefits. Many authors have described the physiological, psychological and biochemical benefits of yoga. The physiological benefits come from maintaining stability of the sympathetic and parasympathetic nervous system. Yogic practices downregulate the hypothalamic pituitary adrenal axis, and as a result the sympathetic nervous system, leading to a predominance of parasympathetic nervous system. Subsequently, there is a decrease in the effects of “chronic stress” (sympathetic responses).
Predominance of the parasympathetic system is translated to many physiologic benefits like lowering of both systolic and diastolic blood pressure, heart rate, blood glucose levels, salivary cortisol, plasma renin and 24- hour urine epinephrine levels. Studies have shown a decrease in C-reactive protein levels, Interleukin-6 and Lymphocyte- 1B. In general, yoga harmonizes bodily functions by regularizing the cardiovascular, gastrointestinal, neurologic and hormonal systems. The psychological benefits of yoga include improved mood, decreased anxiety and depression. The biochemical benefits of yoga, observed in studies, include decrease in blood glucose, total cholesterol, VLDL, triglyceride and HDL cholesterol with increase in HDL cholesterol, and decrease in testosterone levels in PCOS, etc.
Yoga is for everybody. Yoga differs from conventional aerobic exercise with regards to technique, domination of parasympathetic system, low risk for injury, active control of breathing and low effort. People who incorporate yoga in their exercise regimen report decreased food cravings and regularization of food intake, improvement in amount and quality of sleep, improved muscle tone/flexibility, decreased chronic pain and improved mood. In athletes, yoga can be beneficial in active stretching of fatigued muscles, improving endurance and avoiding injury. In the elderly, yoga can be incorporated as a low-impact exercise regimen to improve kinesthetic awareness, improve posture and balance, thereby decreasing falls. In children and adults alike, yoga can have beneficial effects in improving concentration, memory, mood and social skills. In pregnant women, regular yoga practice can improve musculoskeletal pain, shorten labor and help in regaining abdominal and pelvic tone in the postpartum period. Randomized control trials (RCTs) with yoga have encompassed various diseases including breast cancer, postpartum and maternal anxiety and depression, schizophrenia, eating disorders, Stage I hypertension, prediabetes, multiple sclerosis, post-stroke hemiparesis, postcardiac rehabilitation, arthritis (rheumatoid, knee osteoarthritis), polycystic ovarian syndrome, non-restorative sleep, low back and neck pain, fibromyalgia and more. Most RCTs had positive results. There has been a dramatic increase in the number of RCTs in recent years. In one systematic review, there was no difference seen in the type of yoga practice and achieving positive results. Meta- analysis for most medical conditions confirm mild to moderate evidence toward benefits but also note limitations of various studies (most being small, short-term and low-quality). In a meta-analysis involving 8,430 individuals, the safety of yoga was similar to usual care and exercise.
In summary, yoga is gaining much popularity and becoming increasingly recognized as an important complementary therapy and intervention to improve overall sense of well-being, decrease chronic pain, and improve sleep and mood. The effect of yoga in improving chronic metabolic conditions needs further exploration. Yoga can be safely incorporated after consultation with a physician and a trained/certified yoga instructor.
Further reading 1. Light on Yoga. B. K. S. Iyengar 2. Anantharaman, V., and Sarada Subrahmanyam. Physiological benefits in hatha yoga training. The Yoga Review, 3(1):9-24. 3. Arpita. Physiological and psychological effects of Hatha yoga: A review of the literature. The Journal of The International Association of Yoga Therapists, 1990, 1(I&II):1-28. 4. The Health Benefits of Yoga and Exercise: A Review of Comparison Studies. Alyson Ross et al. J Altern Complement Med. 2010 Jan;16(1):3-12. 5. The Safety of Yoga: A Systematic Review and Meta-Analysis of Randomized Controlled Trials. Cramer H et al. Am J Epidemiol. 2015 Aug 15;182(4):281-93. 6. Effects of yoga on cardiovascular disease risk factors: a systematic review and meta-analysis. Cramer H et al. Int J Cardiol. 2014 May 1;173(2):170-83.