Nobre Anna C, Rao Anling, Owen Gail N
Unilever Food and Health Research Institute, Olivier van Noortlaan 120, Postbus 114, 3130 AC Vlaardingen, The Netherlands.
Asia Pac J Clin Nutr. 2008;17 Suppl 1:167-8.
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 effect on 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 (approximately 20mg). The aim of the current research was to establish this effect at more realistic dietary levels. EEG was measured in healthy, 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 a greater 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.
茶是世界上除水之外饮用最为广泛的饮品。众所周知，茶富含类黄酮抗氧化剂。然而，茶还含有一种独特的氨基酸——L-茶氨酸，它可能会调节人类大脑功能的某些方面。来自人类脑电图（EEG）研究的证据表明，它对大脑有直接影响（朱尼亚等人，《食品科学与技术趋势》，1999年；10卷；199 - 204页）。L-茶氨酸能显著增加阿尔法频段的活动，这表明它能放松大脑而不引起困倦。然而，这种效果仅在高于一杯红茶中通常所含剂量（约20毫克）时才得到证实。当前研究的目的是在更符合实际饮食水平的情况下证实这种效果。对健康的年轻参与者在摄入50毫克L-茶氨酸（n = 16）或安慰剂（n = 19）后的基线以及45、60、75、90和105分钟时进行脑电图测量。在脑电图记录期间，参与者闭眼休息。在L-茶氨酸组中，随着时间推移阿尔法活动的增加幅度更大（相对于安慰剂，p < 0.05）。第二项研究在从事被动活动的参与者中重复了这一效果。这些数据表明，在实际饮食水平下，L-茶氨酸对精神警觉或觉醒的总体状态有显著影响。此外，已知阿尔法活动在注意力的关键方面发挥重要作用，因此进一步的研究集中在了解L-茶氨酸对注意力过程的影响上。
