Acute effects of tea constituents L-theanine, caffeine, and epigallocatechin gallate on cognitive function and mood: a systematic review and meta-analysis

Abstract

A systematic review and meta-analysis was conducted on 11 randomized placebo-controlled human studies of acute effects of tea constituents L-theanine and epigallocatechin gallate, administered alone or in combination with caffeine, on cognitive function and mood. The outcome measures of mood were alertness, calmness, and contentedness, derived from the Bond-Lader scales, and state anxiety, from the State-Trait Anxiety Inventory. Cognitive measures assessed were attentional switch, intersensory attention, and rapid visual information processing. Standardized mean differences between placebo and treatment groups are presented for each study and outcome measure. Meta-analysis using a random-effects model was conducted when data were available for three or more studies. Evidence of moderate effect sizes in favor of combined caffeine and L-theanine in the first 2 hours postdose were found for outcome measures Bond-Lader alertness, attentional switching accuracy, and, to a lesser extent, some unisensory and multisensory attentional outcomes. Moderator analysis of caffeine and L-theanine doses revealed trends toward greater change in effect size for caffeine dose than for L-theanine dose, particularly during the first hour postdose.

L-theanine, unique amino acid of tea, and its metabolism, health effects, and safety

“…In a meta analysis study, in which 11 randomized placebo controlled studies on humans were gathered, the effect of L-Theanine alone or in combination with caffeine given to the human on the cognitive performance and emotional state was examined. 2 hours after taking the L-Theanine and caffeine combination attention and emotional state outputs in a lower level were affected and similar changes were observed after 1 hour mostly with caffeine + L-Theanine combination, less with caffeine alone and the least with L-Theanine alone (Camfield et al, 2014).…”

A Combination of Nootropic Ingredients (CAF+) Is Not Better than Caffeine in Improving Cognitive Functions

“…3 Effects of the three treatment conditions on accuracy scores in the 2-back task (means + S.E.M.). At 90 min, participants were on average 3% more accurate in their response after caffeine than with a placebo pill (p < 0.015) example, it has repeatedly been shown that caffeine and ltheanine added together have different effects on cognition and mood, leading to cognitive benefits not seen when administered alone (Camfield et al 2014;Einother et al 2010;Haskell et al 2008). More research is needed to look into the mechanisms underlying such effects.…”

“…A similar effect is suggested for l-theanine (Nathan et al 2006), although its combined effects with caffeine are more extensively researched. L-theanine is well known for its synergistic effects with caffeine, leading to larger improvements in cognition together than alone (Camfield et al 2014;Einother et al 2010;Haskell et al 2008) and eliminates the vasoconstrictive effects of caffeine (Dodd et al 2015). It should be noted that the study Dodd et al does not show evidence of a synergistic effect of caffeine and l-theanine on cognition.…”

Is tea a healthy source of hydration?

“…A recent systematic review and meta‐analysis (Carnfield et al . ) reported small to moderate effects on cognitive function and mood, which were attributable to L‐theanine and caffeine. Although caffeine is known to increase acetylcholine and dopamine transmission in the brain, implicated in attention and higher cognitive functions, less is known about L‐theanine, which is a highly bioavailable amino acid that is virtually unique to tea.…”