Neurocognitive and gluco-regulatory effects of Panax ginseng

Complementary and Alternative Medicine (CAM) has long been used in the Far East to aid in the recovery and prevention of illness. Ginseng, an over-the-counter herbal product in the UK, is amongst these herbal CAMs currently available to the general public. Ginseng is renowned for its rejuvenating properties and its purported ability to aid cognitive function and well-being. Despite the huge global market for ginseng there is little in the way of human research, utilising standardised ginseng extracts and well controlled methodology to support many of these claims. Additionally, ginseng's underlying mechanisms of action are poorly understood. The present thesis documents 5 double-blind, placebo-controlled, cross-over trials investigating the effects of Panax ginseng, following acute and chronic ingestion, on behaviour, mood and indices of glucose regulation in young healthy volunteers. The results of the five studies making this thesis suggest that both acute and chronic dosing with Panax ginseng is capable of modulating mood and cognitive performance in healthy young volunteers. Chapters 2 and 3 also demonstrate, for the first time, Panax ginseng's ability to modulate blood glucose levels following a single acute dose in overnight fasted healthy volunteers. In chapters 2 and 3, significant reductions in blood glucose levels and concomitant improvements in mental arithmetic (working memory) performance were reported. Chapter 4 revealed for the first time Panax ginseng's positive effects on traditional measures of working memory, thus posing the suggestion that previous failures to report working memory effects (using traditional working memory tasks) may have been due to poor task selection. Chapter 5 revealed an unexpected superimposed relationship between chronic and acute ingestion of Panax ginseng. The pattern of results suggests that following chronic dosing, an acute dose can further modulate cognition and mood (suggestive of a psychological dependence). The final chapter documents a different profile of cognitive and mood effects following a non-standardised Panax ginseng extract, thus highlighting the need for caution when generalising results across ginseng types and beyond the specific parameters of the methodologies utilised in any given study. Methodological differences between studies may go some way in explaining the inconsistent data patterns reported between studies, research groups and ginseng extracts. These data further highlight the need for well-controlled studies utilising standardised ginseng extracts and the need for the integration of 'theory driven' research in order to fractionate any behavioural effect. Such methodologies will inevitably lead to greater consistency between behavioural studies, at least in the first instance within the restricted population of volunteers utilised in the present thesis