Published online May 20, 2022. doi: 10.5662/wjm.v12.i3.132
Peer-review started: December 3, 2021
First decision: February 8, 2022
Revised: February 16, 2022
Accepted: April 3, 2022
Article in press: April 3, 2022
Published online: May 20, 2022
Ayurveda is the Indian traditional system of medicine, and has a history since the 2nd century BC. Many Ayurvedic preparations have been anecdotally claimed to have immune-boosting properties and have been used for immune enhancement and general well-being. Pre-clinical research suggests that the immune enhancement is mediated through multiple immune system modulation and psychoneuroimmunological mechanisms.
We were interested to know the exact mechanisms of immune enhancement by Ayurvedic preparations when they are administered to healthy or sick humans.
The objectives of the present systematic literature review were to gather evidence towards the nature and mechanism of enhancement of human immune system by the administration of Ayurvedic preparations from published randomized clinical trials (RCTs).
We prospectively registered the study protocol with PROSPERO. Based on predetermined eligibility criteria, search strategy was formulated and refined, and the same was used to search PubMed, DOAJ, Google Scholar, three dedicated Ayurveda research portals, two specialty Ayurveda journals, and reference lists for relevant records published until February 6, 2021. Baseline features and data pertaining to the nature and mechanism of immune system function were extracted from all eligible records. Methodological quality was assessed using the Cochrane RoB-2 tool.
Our search strategy yielded a total of 12554 articles, and we found 19 studies reporting 20 RCTs (17 parallel group design, three crossover design) with 1661 unique patients to be eligible for inclusion. Healthy population was included in nine studies, of which one study included pregnant women and two included pediatric population; remaining studies included patients with different health conditions. A total of 21 Ayurvedic interventions were studied, out of which five were composite mixtures. Through indirect evidence, four interventions were seen to be associated with immune enhancement, and two interventions were associated with a lack of such an enhancement. The role of T helper cell and natural killer cell enhancement was reported to contribute to the enhancement of immune systems by three and four interventions, respectively. Evidence pointing to enhancement of other immune system components, including cytotoxic T cells, B lymphocytes, immunoglobulins, cytokines, complement components, leucocyte counts, and other components, was not found. Risk of bias was 'high' in 9/20 RCTs, and 'some concerns' of bias were found in the remaining 11/20 RCTs, according to RoB-2.
Various Ayurvedic preparations, both standalone and composite, appear to have an enhancing effect on the immune system, as evidenced indirectly through reduced illness variables, but the exact mechanism behind this enhancement is not fully established. There may be contributions from enhancement of natural killer cells and T helper cells, although the role of other immune system components is not clear.
There is a need to improve the quality of research in Ayurveda. Ayurvedic scholars should team up with experts of modern clinical research and generate credible and reproducible evidence towards immune system enhancement. This will enable widespread acceptance of the immense knowledge of Ayurveda, leading to its increased usage, and ultimately, a healthier society.