Yoga’s growing evidence base

There have been numerous claims made for the benefits of yoga both in ancient texts and in modern times. The Hatha Yoga Pradipika, for example talks about some pranayama practices as being able to “destroy disease” and particular asana’s being able to “cure” disease. In current times, websites abound with talk of the physical and mental effects of a regular yoga practice, and trials more acceptable in modern Western healthcare have been publicised studying yoga as an intervention in areas such as back pain and hypertension.

As both a yoga teacher and a pharmacist, I have a keen interest in the evidence surrounding interventions used in healthcare. I was curious to see just how much work on yoga has been published in biomedical journals over recent decades. Therefore, I carried out a search using PubMed on the Internet. PubMed is a search engine which is free to use with no registration required. It mainly searches Medline, which is a database on life sciences and biomedical topics that is maintained by the U.S. National Library of Medicine. Medline contains over 21 million references to journal articles in life sciences. It contains citations from over 5,600 worldwide journals in about 40 languages.

In Medline, records are indexed with medical subject headings known as MeSH descriptors. MeSH descriptors are arranged hierarchical structures, referred to as “trees”. At the most general level of the tree are very broad headings, with more specific headings at narrower levels. There are 27,149 descriptors in 2014 MeSH. I decided to see if “yoga” was listed as a Mesh descriptor.  I was surprised to find that it was indeed a MESH descriptor and interestingly the following definition from Webster’s dictionary is given: “A major orthodox system of Hindu philosophy based on Sankhya (metaphysical dualism) but differing from it in being theistic and characterized by the teaching of raja-yoga as a practical method of liberating the self. It includes a system of exercises for attaining bodily or mental control and well-being with liberation of the self and union with the universal spirit. (From Webster, 3d ed)”

Searching on “Yoga” as a Medical Subject Heading (MeSH) alone in PubMed retrieved 1603 articles.  Looking at the number of publications per year reveals the following spread. It perfectly illustrates how the interest in studying yoga has increased over the years. There was even one article published in 1948 that I was interested in looking at, but unfortunately it was in an “undetermined language” and with no abstract available!

New Picture

The MeSH descriptor “yoga” appears in two broad categories “Analytical, Diagnostic and Therapeutic Techniques and Equipment Category” and also the “Humanities Category”, with the tree structures as follows. One relating to therapy and one relating to religious philosophies, perhaps representing the the breadth that yoga can span as a system, the therapeutic application of yoga as well as the philosophy.

Analytical, Diagnostic and Therapeutic Techniques and Equipment Category
-Therapeutics
–Complementary Therapies
—Spiritual Therapies
—-Yoga

Humanities Category
-Religion
–Religious Philosophies
—Yoga

According to the NLM website (http://www.nlm.nih.gov/mesh/intro_trees.html), “The indexing should not be regarded as representing an authoritative subject classification system but rather as arrangements of descriptors for the guidance and convenience of persons who are assigning subject headings to documents or are searching for literature. The trees are not an exhaustive classification of the subject matter but contain only those terms that have been selected for inclusion in this thesaurus. Their structure frequently represents a compromise among the views and needs of particular disciplines and users, in the absence of any single universally accepted arrangement”.  However, the appearance of yoga under a broader heading of religion is interesting considering the controversy that occasionally occurs around yoga and whether it is a religion. 

I hadn’t  quite appreciated just how much published literature about yoga exists in scientific and biomedical journals until I carried out this exercise. However, as Pattabhi Jois once said “99% practice, 1% theory”!