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Systematic review/Review Articles

Effects of L-Theanine, a Constituent of Tea, on Cognitive Functions and Attention

Authors:

U. W. Karunaratne ,

University of Peradeniya, LK
About U. W.
Department of Physiology, Faculty of Medicine
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D. Karunaratne,

University of Peradeniya, LK
About D.
Department of Physiology, Faculty of Medicine
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S. Karunaratne,

University of Peradeniya, LK
About S.
Department of Physiology, Faculty of Medicine
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G. Karunasena,

University of Peradeniya, LK
About G.
Department of Physiology, Faculty of Medicine
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S. Kodikara,

University of Peradeniya, LK
About S.
Department of Physiology, Faculty of Medicine
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H. Kaushalya,

University of Peradeniya, LK
About H.
Department of Physiology, Faculty of Medicine
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C. Wikum,

University of Peradeniya, LK
About C.
Department of Physiology, Faculty of Medicine
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K. Navakulan,

University of Peradeniya, LK
About K.
Department of Physiology, Faculty of Medicine
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H. Kaflay,

University of Peradeniya, LK
About H.
Department of Physiology, Faculty of Medicine
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S. Kathriarachchi,

University of Peradeniya, LK
About S.
Department of Physiology, Faculty of Medicine
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R. Kiriwandala,

University of Peradeniya, LK
About R.
Department of Physiology, Faculty of Medicine
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T. L. Dassanayake

University of Peradeniya, LK
About T. L.

Department of Physiology, Faculty of Medicine

 

School of Psychological Sciences, University of Newcastle, Australia

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Abstract

Tea (Camellia sinensis) is a historically and economically important beverage for Sri Lanka; and is traditionally believed to have relaxing or calming effects. Some evidence attributes these effects to a constituent of tea leaves; L-theanine, a non-protein-forming amino acid structurally similar to glutamic acid. Over the years, research has found L-theanine to also have effects on various cognitive functions, including attention. This review focuses on the research conducted thus far on the acute effects of L-theanine on neurobehavioral, neurophysiological, and functional neuroimaging indices, cognition and attention. Despite the heterogeneity of testing paradigms across studies, experimental evidence increasingly suggests that L-theanine could improve visual selective attention. Contrary to traditional belief, the amount of L-theanine in a cup of tea (4.5-22.5mg) seems to cause no significant effects; and attentional improvement is more prominent with much higher doses (100-500mg). This makes it worth exploring the possibility of enriching tea with L-theanine, while preserving the unique flavour of the product. L-theanine has an additive effect with caffeine in enhancing attention, but unlike caffeine, L-theanine can be ingested in high doses with no risk of adverse effects, tolerance or dependence. The evidence on attentional effects of L-theanine is almost entirely based on healthy samples who have undergone laboratory-based attentional tasks that employed abstract stimuli.  When translating these laboratory findings to real-life scenarios, incorporating more real-life-based stimulus paradigms (i.e., simulated driving scenarios) is warranted. The clinical relevance of L-theanine research could also be improved by exploring the effects of L-theanine in cognitively compromised groups of individuals.

How to Cite: Karunaratne, U.W., Karunaratne, D., Karunaratne, S., Karunasena, G., Kodikara, S., Kaushalya, H., Wikum, C., Navakulan, K., Kaflay, H., Kathriarachchi, S., Kiriwandala, R. and Dassanayake, T.L., 2022. Effects of L-Theanine, a Constituent of Tea, on Cognitive Functions and Attention. Sri Lanka Journal of Medicine, 31(1), pp.58–69. DOI: http://doi.org/10.4038/sljm.v31i1.332
Published on 15 Aug 2022.
Peer Reviewed

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