The title of the study is about 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. This study was written by Dodd FL, Kennedy DO, Riby LM, Haskell-Ramsay CF, and assisted by Anthea Wilde in running the salivary assays and Dr. Philippa Jackson for her statistical advice in 2015.
Evidence suggests interactive effects of the tea components caffeine and L-theanine on behavior. Yet no data exists exploring the impact of the two on cerebral blood flow (CBF).
Hence the objective of the study is to examine the effects of caffeine and L-theanine on CBF and extended previous cognitive and mood findings by …show more content…
Volunteers were recruited to take part in the study if they fell into one of two pre-defined categories: ‘habitual consumers’ (those who drank tea and consumed more than 150 mg caffeine per day) or ‘non-habitual consumers’ (those who consumed less than 60 mg caffeine per day and no more than 2 cups of tea/coffee per week).
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. Salivary caffeine and peripheral hemodynamics were co-monitored. However, only non-smoking volunteers who were in good health, not currently taking any dietary supplements or medication were recruited to take part in the study to ensure that no other factors would affect the …show more content…
Mean baseline values were 0.34 μg/ml and confirmed overnight abstinence [levels below 1 μg/ml have previously been reported for overnight caffeine abstinence. Following caffeinated treatment, salivary caffeine levels were 2.25 μg/ml (combination) and 2.33 μg/ml (caffeine). Analysis of the results confirmed that in comparison to baseline levels, salivary caffeine was significantly higher following caffeine and combination treatments [F(1, 23) = 63.27, p < 0.0001], with no significant difference between treatments.
The conclusion of the study was that by 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.
In relation to the behavioural effects, caffeine significantly reduced choice reaction time, improved Stroop performance and improved subjective ratings of overall mood.