Neurocognitive and physiological effects of Tulsi tea

Holy basil commonly referred to as tulsi is a highly revered Ayurvedic herb used for centuries in Traditional Indian Medicine as a natural metabolic regulator of stress homeostasis known as adaptogen to treat a range of conditions, especially metabolic and cardiovascular disorders. Pre-clinical and clinical studies suggest that tulsi has both psychological and physiological health benefits. While a number of clinical studies attest to the chronic health benefits of tulsi, to date there are no studies reporting on the health effects of acute oral ingestion of tulsi in humans. The main research aim of this thesis was therefore focused on exploring the transient effectiveness of aqueous tulsi as a hot beverage on a range of psychological and physiological responses in healthy individuals. Firstly, the clinical evidence on the effects associated with oral ingestion of tulsi leaf extract in health and disease was reviewed systematically. The methodology followed the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guideline where several general databases were searched, and eligible studies screened against inclusion criteria. The findings of this systematic review support traditional uses of tulsi with documented therapeutic effects on chronic conditions including improvement in metabolic disorders, cardiovascular disease, immunity and neurocognition domains. Cardiometabolic conditions, specifically metabolic syndrome, were identified as the most studied and this led to a novel meta-analysis to quantitatively determine the efficacy of tulsi consumption on cardiometabolic parameters. The meta-analysis revealed that fasting blood glucose and lipid profiles are consistently improved in individuals who consumed tulsi as a single herb in all the identified randomised controlled trials irrespective of the form of extract. Furthermore, the available evidence suggests that consumption of doses of tulsi ≥1g/day in older individuals (≥40 years) with a chronic metabolic disorder is safe and can reduce total cholesterol, low-density lipoprotein and very low-density lipoprotein without changing overall lipid profiles. These two research reviews have added new knowledge to the literature on tulsi and confirm the effective dosage range and its efficacy in treatment of cardiometabolic conditions. Both systematic review and meta-analysis revealed a gap in the literature where no acute effects of tulsi have been assessed by a clinical trial. To address this gap in the literature, we assessed the acute effects of tulsi on neurocognitive and psychological responses over time in order to explore links to chronic effects. Prior to this clinical trial, a further systematic review was conducted to identify possible mechanisms underlying the acute clinical effects of tulsi and the time course of any relevant changes. A search of electronic databases identified 11 studies reporting on acute intake of plant dietary interventions with significant changes detected in transcriptomic response involving inflammatory, immune, cancer and oxidative stress pathways within an hour after intake. Based on the knowledge gained from the systematic reviews and meta-analysis, a randomised, controlled, double-blind, crossover trial involving 35 healthy adults was designed. Over two sessions separated by a one-week washout period, the participants received either a cup of tulsi tea or decaffeinated black tea. On each day, blood pressure, mood, salivary cortisol and cognitive performance were assessed in that order at baseline and 40 minutes post-tea consumption. Consistent with evidence from preclinical studies, the clinical findings revealed a significant decrease in anxiety, depression and arterial stiffness post-tulsi tea not evident post-control tea ingestion. In particular, due to tulsi tea a differential subjective mood, cognitive and cardiovascular response was detected in female participants based on habitual caffeine consumption. Future research on the clinical effects of tulsi needs to account for gender, adiposity, age and habitual caffeine consumption. Given the exploratory nature of this clinical study together with sample size limitations and ineffectiveness of tulsi tea for some of the subpopulations, these findings need to be interpreted with caution and confirmed in controlled large scale clinical studies to determine if a daily cup of tulsi tea offers adaptogenic benefits as part of a healthy lifestyle.