Asia Pac J Clin Nutr 2008;17 (S1):167-168

167

Original Article

L-theanine, a natural constituent in tea, and its effect onmental state
Anna C Nobre PhD2, Anling Rao PhD2 and Gail N Owen PhD1
12

Unilever Food and Health Research Institute, Vlaardingen, The Netherlands
Department of Experimental Psychology, Oxford University, UK
Tea is the most widely consumed beverage in the world after water. Tea is known to be a rich source of flavonoid antioxidants. However tea also contains a unique amino acid, L-theanine that may modulate aspects of brain
function in humans. Evidence from human electroencephalograph (EEG) studies show that it has a direct effecton the brain (Juneja et al. Trends in Food Science & Tech 1999;10;199-204). L-theanine significantly increases
activity in the alpha frequency band which indicates that it relaxes the mind without inducing drowsiness. However, this effect has only been established at higher doses than that typically found in a cup of black tea (~20mg).
The aim of the current research was to establish this effect at more realistic dietary levels. EEG was measured inhealthy, young participants at baseline and 45, 60, 75, 90 and 105 minutes after ingestion of 50mg L-theanine(n=16) or placebo (n=19). Participants were resting with their eyes closed during EEG recording. There was agreater increase in alpha activity across time in the L-theanine condition (relative to placebo (p<0.05). A second
study replicated this effect in participants engaged in passive activity. These data indicate that L-theanine, at realistic dietary levels, has a significant effect on the general state of mental alertness or arousal. Furthermore, alpha activity is known to play an important role in critical aspects of attention, and further research is therefore
focussed on understanding the effect of L-theanine on attentional processes.

Key Words: L-theanine, tea, alpha, EEG, attention

INTRODUCTION
Theanine, (γ-glutamylethylamide) is a non-protein aminoacid found in species of Camellia3,4 and in the edible bay
boletes mushroom Xerocomus badius4 but is otherwise rarein nature. It is the major amino acid in tea and is thought tobe a flavourous constituent of tea leaves. It constitutes between 1 and 2% of the dry weight of tea3 which corresponds
to 25-60mg per 200ml serving. Within tea the predominant
form of theanine is the L isomer.
L- theanine is thought to cross the blood-brain barrier toexert its effects directly on the brain within 30 minutes.11
Its central effects were first reported in humans following arandomised, placebo-controlled, crossover study comparing placebo, 50 and 200mg L-theanine. The study wasoriginally published in Japanese7 and later reviewed in
English.8 Relative to placebo, the higher dose of L-theanine
increased power in the alpha frequency band (8-13Hz) of
the electroencephalogram (EEG) across parietal and occipital sites after approximately 40min.
However, L-theanine was effective only in participants
classified as highly anxious using a manifest anxiety scale.
A more recent study has since confirmed that L-theanine ismost effective in individuals who generally have highlevels of anxiety.9
In the current study, the effect of L-theanine on the resting brain activity in young healthy human volunteers wasinvestigated. The aim of was to measure changes in brain
activity within the alpha frequency band of the EEG at
different doses, in order to replicate and extend the findings

from previous examination of the effects of L-theanine
upon brain activity.
SUBJECTS AND METHODS
Sixteen participants (11F, 5M) were assigned to the Ltheanine group and a further 19 (12F, 7M) to the control
group. The control solution was 100 ml of cool potablewater and the L-theanine solution was prepared by dissolving 0.5 mg powdered L-theanine (Taiyo Kaguka Co. Ltd.,
Yokkaichi, Japan) per Kg participant body weight in a tea
infusion (total L-theanine 50mg/serving).
EEG activity was recorded using either Ag/AgCl electrodes mounted on an elastic cap (Electro-Cap Inc.) andpositioned according to the 10-20 International system(AEEGS 1991).
The first EEG sample was collected 45 minutes after ingestion and measured subsequently every 15 minutes (45, 60,75, 90, 105 minutes. Epochs of EEG containing 8,192 pointsof data for each electrode were saved from each 60-second
measurement trial and analysed off line. Average power(µV2) was computed using a cosine transformation: alpha 1(8-10Hz) and alpha 2 (11-13Hz).
Corresponding Author: Dr G.N. Owen, Unilever Food andHealth Research Institute, Olivier van Noortlaan 120, Postbus
114, 3130 AC Vlaardingen, The Netherlands
Tel: +31-10-4606486; Fax: +31-10-4605236
Email: gail.owen@unilever.com
Manuscript reveive 9 September 2007. Accepted 3 December
2007.

168

AC Nobre, A Rao and GN Owen

The ethics committee at the Department of Experimental Psychology, University of Oxford approved each of
the studies and all participants provided written informed
consent before taking part.
Control(water)

L-theanine(50mg)

ACKNOWLEDGEMENTS
This study was performed at the Brain and Cognition Laboratory, Oxford University, UK. The authors wish to acknowledge
the contribution of Dr Jane Rycroft, Unilever Research & Development, UK.

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0.6
0.5
0.4

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under this situation in which participants are alreadyhighly relaxed and entertained.
Furthermore, activity in the alpha-band is also a key
component in focused attentional processes.2,5 Directed
deployment of alpha appears to be critical to the ability tosuppress distracting visual information during highly demanding tasks. Recently, L-theanine has also been shownto enhance this so-called alpha attention effect also. 60.3

μV20.2AUTHOR DISCLOSURES
Gail Owen is an employee of Unilever, which markets foodproducts some of which contain L-theanine and caffeine.

0.1090105
minutesFigure 1. Average power plotted on a schematic top-view of thescalp for L-theanine and control at five successive times after ingestion. Activity was higher in the L-theanine group than in thecontrol for alpha-1 (p<0.05).

RESULTS
The alpha-1 band showed significant main effects of time[F (4,104) = 5.20, p <.05] and condition [F (1,26) = 5.825,p < .05]. Alpha activity increased over time and wasgreater in the L-theanine group (Figure 1). There was alsoa marginally significant interaction between the factors[F(4,104) = 2.42, p = .05]. A significant linear contrast
for the interaction between drink condition and time
showed a greater increase of alpha activity over time inthe L-theanine condition [F (1,26) = 4.51, p < .05]. In thealpha-2 band, a linear contrast showed a main effect oftime [F (1,26) = 6.56, p < .05] but there was no effect ofcondition or an interaction of these factors.
DISCUSSION
The current study demonstrated that L-theanine significantly modulates the resting state of brain activity. Ltheanine enhanced the power in the alpha-1 frequency
band, replicating previous reports.7,10 In the current experiment, the power in the alpha band increased linearlywith time and this linear increase was significantly enhanced by L-theanine. This increase in alpha-band activity supports a role for L-theanine in achieving a relaxed
but alert mental state via a direct influence on the central
nervous system.
These results have since been replicated under ecologically valid conditions in which participants passively
watched television (unpublished). It was notable that Ltheanine was able to elevate the level of alpha-1 even

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