title: 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.
abstract: BACKGROUND
  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).
  
  
  OBJECTIVE
  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.
authors.affiliation: Brain, Performance and Nutrition Research Centre, Faculty of Health and Life Sciences, Northumbria University, Newcastle upon Tyne, NE1 8ST, UK.
authors.forename: F L
authors.initials: FL
authors.lastname: Dodd
authors.forename: D O
authors.initials: DO
authors.lastname: Kennedy
authors.forename: L M
authors.initials: LM
authors.lastname: Riby
authors.forename: C F
authors.initials: CF
authors.lastname: Haskell-Ramsay
mesh_terms: D000293:Adolescent; D000328:Adult; D000339:Affect / Q000187:drug effects*; D001288:Attention / Q000187:drug effects; D002110:Caffeine / Q000378:metabolism / Q000494:pharmacology*; D000697:Central Nervous System Stimulants / Q000378:metabolism / Q000494:pharmacology*; D002560:Cerebrovascular Circulation / Q000187:drug effects*; D003071:Cognition / Q000187:drug effects*; D018592:Cross-Over Studies; D004311:Double-Blind Method; D005260:Female; D005971:Glutamates / Q000494:pharmacology*; D006439:Hemodynamics / Q000187:drug effects; D006454:Hemoglobins / Q000378:metabolism; D006801:Humans; D008297:Male; D010108:Oxyhemoglobins / Q000378:metabolism; D011597:Psychomotor Performance / Q000187:drug effects; D011930:Reaction Time / Q000187:drug effects; D019265:Spectroscopy, Near-Infrared; D014661:Vasoconstriction / Q000187:drug effects; D055815:Young Adult
chemical_list: D000697:Central Nervous System Stimulants; D005971:Glutamates; D006454:Hemoglobins; D010108:Oxyhemoglobins; D002110:Caffeine; C026166:theanine; C100003:deoxyhemoglobin