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Randomized Controlled Trial
. 2015 Jul;232(14):2563-76.
doi: 10.1007/s00213-015-3895-0. Epub 2015 Mar 13.

A Double-Blind, Placebo-Controlled Study Evaluating the Effects of Caffeine and L-theanine Both Alone and in Combination on Cerebral Blood Flow, Cognition and Mood

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Free PMC article
Randomized Controlled Trial

A Double-Blind, Placebo-Controlled Study Evaluating the Effects of Caffeine and L-theanine Both Alone and in Combination on Cerebral Blood Flow, Cognition and Mood

F L Dodd et al. Psychopharmacology (Berl). .
Free PMC article

Abstract

Rationale: Evidence suggests interactive effects of the tea components caffeine and L-theanine on behaviour, yet no data exists exploring the impact of the two on cerebral blood flow (CBF).

Objectives: The current placebo-controlled, double-blind, counterbalanced, crossover study examined the effects of caffeine and L-theanine on CBF and extended previous cognitive and mood findings by using lower doses than previous studies of a similar methodology, which more closely reflect the ratios present in tea.

Methods: Twelve habitual consumers and 12 non-habitual consumers of caffeine each received 75 mg caffeine, 50 mg L-theanine, 75 mg caffeine plus 50 mg L-theanine, and placebo in a counterbalanced order across four separate visits. CBF was measured via near-infrared spectroscopy with cognition and mood assessed at baseline and 30 min post-dose. Salivary caffeine and peripheral haemodynamics were co-monitored.

Results: Caffeine reduced oxygenated haemoglobin (oxy-Hb), increased deoxygenated haemoglobin (deoxy-Hb), improved performance on attention tasks and increased overall mood ratings. Increases in deoxy-Hb following caffeine were more pronounced in non-consumers. Some evidence for increased deoxy-Hb remained when caffeine was combined with L-theanine, but this effect was attenuated and the effects of caffeine on oxy-Hb, cognition and mood were eradicated.

Conclusions: Combining L-theanine with caffeine, at levels and ratios equivalent to one to two cups of tea, eliminated the vasoconstrictive effect and behavioural effects of caffeine. This supports previous findings of an interaction between these substances, despite a lack of effects of L-theanine in isolation. However, at the levels tested here, this did not lead to a positive impact on behaviour.

Figures

Fig. 1
Fig. 1
Timeline representing flow of study day
Fig. 2
Fig. 2
Mean change in concentration of NIRS parameters (oxy-Hb and deoxy-Hb) during absorption period and cognitive tasks following placebo (circle), 50 mg L-theanine (inverted triangle), 75 mg caffeine (square) and a combination of 50 mg L-theanine and 75 mg caffeine (diamond). Treatment × epoch interaction effects are shown for a oxygenated haemoglobin and b deoxygenated haemoglobin (*p < 0.05; ** p < 0.01; *** p < 0.005; **** p < 0.001)
Fig. 3
Fig. 3
Mean change in concentration of deoxy-Hb overall following placebo, 50 mg L-theanine (L-thea), 75 mg caffeine (Caff) and a combination of 50 mg L-theanine and 75 mg caffeine (Combi) per consumer status. Treatment × consumer status interaction effects are shown for deoxygenated haemoglobin (***p < 0.005)

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