Nature and mechanism of immune boosting by Ayurvedic medicine: A systematic review of randomized controlled trials

BACKGROUND: Many Ayurvedic preparations are claimed to have immune-boosting properties, as suggested in various published randomized clinical trials (RCTs) AIM: To compile evidence on the nature and mechanism of immune system enhancement by Ayurvedic preparations in healthy and sick individuals. METHODS: After prospectively registering study protocol with PROSPERO, we searched PubMed, DOAJ, Google Scholar, three dedicated Ayurveda research portals, two specialty Ayurveda journals, and reference lists for relevant records published until February 6, 2021 using appropriate search strategies. 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. RESULTS: Of 12554 articles screened, 19 studies reporting 20 RCTs (17 parallel group design, three crossover design) with 1661 unique patients were included; 11/19 studies had Indian first authors. 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, including one study with coronavirus disease 2019 patients. A total of 21 Ayurvedic interventions were studied, out of which five were composite mixtures. The predominant route of administration was oral; dose and frequency of administration of the intervention varied across the studies. The results reported with five RCTs exploring five Ayurvedic interventions were incomplete, ambiguous, or confusing. Of the remaining 16 interventions, indirect evidence of immune enhancement was reported with four interventions, while lack of the same was reported with two interventions. Enhancement of T helper cells and natural killer cells was reported with three and four interventions, respectively, while the pooled results did not clearly point toward enhancement of other components of the immune system, including cytotoxic T cells, B lymphocytes, immunoglobulins, cytokines, complement components, leucocyte counts, and other components. Nine of the 20 RCTs had a high risk of bias, and the remaining 11 RCTs had some concerns according to RoB-2. CONCLUSION: Various Ayurvedic preparations appear to enhance the immune system, particularly via enhancements in natural killer cells and T helper cells.