Yoga is a general term for the physical, mental, and spiritual practices or disciplines which originated in ancient India to achieve a state of permanent peace. Yoga is a Sanskrit word which means "union" and is interpreted as "union with the divine". Thus, yoga can be a spiritual or even a religious activity. In the late 19th century, yoga was brought to the Western World by Hindu monks. [Wikipedia] And now, yoga is a popular physical exercise across the world.
Yoga has been promoted to have a wide variety benefits, especially anti-aging. Some promoters claim that yoga is a gentle form of exercise, as far as you perform it every day of the week, it will help you to build muscle, relieve tension and pain, and increase flexibility. They also suggest to you that the emotional benefits of serious yoga practice. To validate what they claim, I have reviewed multiple scientific articles and summarize their observations in this article . ____________________________________________________________________________________________
Arguments and Scientific Evidence
1. Does yoga practice help depression? Regarding severity of depression, researchers found a moderate or limited evidence for short-term effects of yoga.  Yes, yoga does have benefits on people at risk of depression.
2. Does yoga practice benefit people at risk of anxiety? Limited evidence was found for short-term effects of yoga on anxiety. 
3. Can yoga practice be a part of Pain Management? Only weak recommendations can be made for the ancillary use of yoga in the management of FM syndrome, OA and RA at this point.  It is unclear if yoga practice benefits people with pain.
4. Does yoga practice improve balance? The evidence for outcome was generally from only a few of the trials for each exercise category.  It is still unclear about its benefit on balancing.
5. Does yoga practice improve flexibility? Yoga exercise improved BMI, flexibility, and muscular endurance in a study of 30 subjects.  Yoga may have such health benefits.
7. Does yoga practice benefit heart rate, blood pressure? The biological effects of yoga may include decreased heart rate, blood pressure, body weight and muscle strength. Researchers suggested that the underlying mechanism may include stimulation of pressure receptors leading to enhanced vagal activity and reduced cortisol.  ____________________________________________________________________________________________
When I was reviewing scientific articles about yoga, I found some interesting potential benefits about yoga that promoters seldom mention:
Yoga Benefits and Pregnancy, Reproductivity 1. Regular yoga practice from childhood is beneficial for reproductive health.  2. Yoga can potentially be an effective therapy in reducing hypertensive related complications of pregnancy and improving fetal outcomes.  3. A 12-week Yoga-focused educational program can be utilized for women pregnant following in vitro fertilization to reduce their stress, anxiety, and labor pain, and to increase delivery confidence.  4. Following 12 weeks of twice weekly yoga or massage therapy sessions, both therapy groups versus the control group had a greater decrease on depression, anxiety and back and leg pain scales and a greater increase on a relationship scale. 
Yoga Benefits and Cancer The evidence for efficacy of yoga as an alternative and complementary treatment for cancer is mixed, although generally positive.  Yoga may not have a direct benefit on those suffered from cancer, but it does help in some ways. Here is a summary of a few recent reports: 1. Thirty percent to 90% of cancer survivors report impaired sleep quality post-treatment, Preliminary evidence suggests that yoga-a mind-body practice and form of exercise-may improve sleep among cancer survivors.  2. Results of the studies included in this review suggest that yoga interventions may be beneficial for reducing cancer-related fatigue in women with breast cancer.  3. Yoga, with an emphasis on postures coordinated with breathing and meditation practices, offers a potentially feasible and beneficial option for patient suffered from lung cancer.  ___________________________________________________________________________________________
Conclusions and Comments
Yoga may offer lot more health benefits than we can imagine, but we just don't have sufficient scientific data to support most of the claims. But, yoga involves certain types of poses, incorrect practice may lead to injury. Yoga trainees must consult with their medical doctor before practising yoga. ____________________________________________________________________________________________
 Cramer H et al, Yoga for depression: a systematic review and meta-analysis. Depress Anxiety 2013 Aug. 6  Cramer H et al, Yoga for rheumatic diseases: a systematic review. Reumatology (Oxford). 2013 Aug 9  Howe TE et al, Exercise for improving balance in older people, Cochrane Database Syst Rev. 2011 Nov. 9(11)  Chen Tl et al, The effect of yoga exercise intervention on health related physical fitness in school-age asthmatic children, Hu Li Za Zhi 2009 Apr., 56(2): 42-52.  Field T, Yoga clinical research review. Complement Ther Clin Pract., 2011 Feb; 17(1)1-8.  Sengupta P, et al, Male reproductive health and yoga. Int J Yoga. 2013 Jul;6(2):87-95.  Rakhshani A, et al, The effects of yoga in prevention of pregnancy complications in high-risk pregnancies: a randomized controlled trial. Prev Med. 2012 Oct;55(4):333-40  Shim CS, Lee YS. Effects of a yoga-focused prenatal program on stress, anxiety, self confidence and labor pain in pregnant women with in vitro fertilization treatment. J Korean Acad Nurs. 2012 Jun;42(3):369-76.  Field T et al, Yoga and massage therapy reduce prenatal depression and prematurity. J Bodyw Mov Ther. 2012 Apr;16(2):204-9.  Mustian KM, et al, Multicenter, randomized controlled trial of yoga for sleep quality among cancer survivors. J Clin Oncol. 2013 Sep 10;31(26):3233-41.  Sadja J, Mills PJ. et al, Effects of yoga interventions on fatigue in cancer patients and survivors: a systematic review of randomized controlled trials. Explore (NY). 2013 Jul-Aug;9(4):232-43.  M Fouladbakhsh J, et al, Using a standardized Viniyoga protocol for lung cancer survivors: a pilot study examining effects on breathing ease. J Complement Integr Med. 2013 Jun 26;10  Sharma M, et al, Yoga as an Alternative and Complementary Treatment for Cancer: A Systematic Review. J Altern Complement Med. 2013 Mar 12.