Cerebral blood flow and behavioural effects of caffeine in habitual and non-habitual consumers of caffeine: A near infrared spectroscopy study

Abstract

Caffeine has been shown to modulate cerebral blood flow, with little evidence of tolerance to these effects following habitual use. However, previous studies have focused on caffeine levels much higher than those found in dietary servings and have compared high caffeine consumers with low consumers rather than 'non-consumers'. The current placebocontrolled double-blind, balanced-crossover study employed Near Infrared Spectroscopy to monitor pre-frontal cerebral-haemodynamics at rest and during completion of tasks that activate the pre-frontal cortex. Twenty healthy young habitual and non-habitual consumers of caffeine received 75mg caffeine or placebo. Caffeine significantly decreased cerebral blood flow but this was subject to a significant interaction with consumption status, with no significant effect being shown in habitual consumers and an exaggerated effect in non-habitual consumers. These findings suggest that caffeine, at levels typically found in a single dietary serving, is able to modulate cerebral blood flow but these effects are subject to tolerance.

Acute effects of brewed cocoa consumption on attention, motivation to perform cognitive work and feelings of anxiety, energy and fatigue: a randomized, placebo-controlled crossover experiment

“…Adequate blood flow to cognition-related neural circuitry is necessary but cognitive performance also appears to depend on a host of excitatory and inhibitory neurotransmitters (e.g., gammaaminobutyric acid and glutamate), neuromodulators (e.g., dopamine and norepinephrine) and neuropeptides (e.g., cholecystokinin, corticotropin releasing factor, galanin) [57]. For example, caffeine can reduce overall and regional brain blood flow [58,59] yet cognitive performance is often improved after caffeine is consumed. Therefore, it is plausible that the effects observed in the present study were not exclusively explained by blood flow changes.…”

The effect of caffeine on working memory load-related brain activation in middle-aged males

“…This dose was chosen to reflect caffeine dosages commonly consumed by habitual coffee drinkers and to minimise physiological side effects such as heart rate, blood pressure, CBF and BOLD response changes (Chen and Parrish, 2009a;Kennedy and Haskell, 2011;Koppelstaetter et al, 2008). The placebo treatment was a cup of decaffeinated instant coffee.…”

“…Therefore, findings from studies examining the effect of caffeine on brain activation in the context of caffeine withdrawal (compared to the withdrawal state as a control condition) may represent the resolution of withdrawal--related activation changes as well as changes relating to the effects of caffeine on CBF and cognition . However, there is evidence that lower caffeine doses do not affect the amplitude or timing of the BOLD response (Chen and Parrish, 2009a) and have a smaller effect (Chen and Parrish, 2009a), or do not significantly affect (Kennedy and Haskell, 2011), CBF. Furthermore, caffeine--related CBF changes are smaller in non--abstained higher consuming habitual users (Addicott et al, 2009).…”

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

“…No effects were observed in this study, which may relate to effects of the known vasoconstrictor caffeine. Given that dietary control was simply limited to assessment taking place $ 2 h post-meal, it is possible that dietary intake of caffeine before participation resulted in a reduction of CBF as previously demonstrated (for example, Cameron et al (157) , Lunt et al (158) , Sigmon et al (159) and Kennedy & Haskell (160) ). Alternatively, caffeine withdrawal may have led to increases in CBF as previously shown (for example, Addicott & Laurienti (16) and Field et al (161) ), making it difficult to demonstrate further superimposed increases.…”