Behavioural effects of compounds co-consumed in dietary forms of caffeinated plants

Research into the cognitive and mood effects of caffeine in human subjects has highlighted some fairly robust and well-accepted effects. However, the majority of these studies have focused on caffeine in isolation; whilst caffeine is normally consumed in the form of plant-derived products and extracts that invariably contain other potentially bioactive phytochemicals. The aim of the present review is to consider the possible mechanisms of action of co-occurring phytochemicals, and any epidemiological evidence suggesting that they contribute to potential health benefits ascribed to caffeine. Intervention studies to date that have been conducted to explore the effects on brain function of the non-caffeine components in caffeine-bearing plants (coffee, tea, cocoa, guarana), either alone or in combination with caffeine, will also be summarised. Research is beginning to accumulate showing independent effects for several of the phytochemicals that co-occur with caffeine, and/or a modulation of the effects of caffeine when it is co-consumed with these naturally concomitant phytochemicals. The present review highlights that more research aimed at understanding the effects of these compounds is needed and, more importantly, the synergistic relationship that they may have with caffeine.