Acute effects of tea constituents L-theanine, caffeine, and epigallocatechin gallate on cognitive function and mood: a systematic review and meta-analysis David A Camfield, Con Stough, Jonathon Farrimond, and Andrew B Scholey 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 post dose. © 2014 International Life Sciences Institute INTRODUCTION Tea, a beverage prepared from the leaves of Camellia sinensis, has been consumed extensively throughout human history. Epidemiological studies have linked the consumption of tea (including green, black, and oolong varieties) to a number of beneficial outcomes for brain health, including a decreased incidence of cognitive decline 1–4 and lower levels of depression and psychologi- cal distress. 5,6 It was not until recent years, however, that randomized controlled trials (RCTs) have been con- ducted to investigate the acute effects of isolated tea con- stituents on cognition and mood. The major constituents of green tea include the tea catechins, which typically account for 30–42% of the dry weight of brewed green tea, along with the amino acid γ-N-ethylglutamine (L-theanine) and caffeine, which contribute around 3% and 2–5%, respectively, to both green and black varieties. 7 The four major tea catechins are (-)-epigallocatechin gallate (EGCG), (-)-epigallocatechin (EGC), (-)- epicatechin gallate (ECG), and (-)-epicatechin (EC). Of these, EGCG is the most prominent, accounting for 50–80% of total catechins. 8 Caffeine is known to increase acetylcholine and dopamine transmission in the brain, due to the inhibition of adenosine (A1 and A2a) receptors, with both of these neurotransmitters implicated in attention, arousal, and higher cognitive functions. Due to caffeine’s rapid absorption following oral consumption, with peak plasma levels being reached within 30 minutes, acute effects on cognitive function and mood would be expected within this time period. 9 In comparison with Affiliations: DA Camfield, C Stough, and AB Scholey are with Centre for Human Psychopharmacology, Swinburne University, Hawthorn, Australia. J Farrimond is with In vitro neuroscience, New Product Research at Glaxo-Smith-Kline, London, UK. Correspondence: A Scholey, Centre for Human Psychopharmacology, Swinburne University of Technology, Mail H24, PO Box 218, Hawthorn, Victoria 3122, Australia. E-mail: andrew@scholeylab.com. Phone: +61-3-9214-8932. Fax: +61-3-9214-5525. Key words: acute, Caffeine, cognition, EGCG, epigallocatechin gallate, meta-analysis, mood, tea, theanine Special Article doi:10.1111/nure.12120 Nutrition Reviews® Vol. 72(8):507–522 507 Downloaded from https://academic.oup.com/nutritionreviews/article/72/8/507/1919604 by guest on 22 July 2022