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茶叶中的成分具有改善记忆功能

【字体: 】【2014-7-3】 【作者/来源 百家乐试玩网】 【阅读: 次】 【关 闭

茶叶是人们日常生活中常见的饮料。关于茶叶改善记忆的功能,在我国很多古代的医学书籍中都有记载,称茶“久食益意思”者有《华佗食论》、称“益思”者有《茶谱》和《茶经》;称“能诵无忘”者有《述异记》;称“使人神思闓爽”者有《本草纲目》;称“醒神思”者有《调变类编》,等等。

近年,随着科学技术的发展,饮茶对人体的记忆和认知功能研究不断深入。英国纽卡斯尔(Newcastle)大学的科学家在2001年首次报道了饮茶对几种与记忆功能相关的酶活性的影响,其中包括乙酰胆碱酯酶、丁酰胆碱酯酶和ß-促分泌酶等。(乙酰胆碱酯酶是一种神经递质,它可以维持神经系统的正常传导,它的正常功能是水解神经触突处释放出的乙酰胆碱,起着调节乙酰胆碱水平的作用。丁酰胆碱酯酶的功能和乙酰胆碱酯酶相似。ß-促分泌酶与老年性痴呆病患者脑中的淀粉样蛋白质的形成有关。目前许多对老年性痴呆患者所用的药物都以降低丁酰胆碱酯酶和ß-促分泌酶为目标,以延缓老年性痴呆病患者的发病过程。)

英国科学家认为,老年性痴呆病患者脑的某些部位出现胆碱能的活性下降。在人的衰老过程中胆碱能会逐渐降低,在发生老年痴呆性疾病和帕金森氏病时会加速这种胆碱能活性的下降过程。绿茶和红茶的提取物都具有抑制乙酰胆碱酯酶和丁酰胆碱酯酶的活性。另外茶叶提取物还可以通过提高α-促分泌酶活性或通过抑制β-促分泌酶活性使得有毒的ß-淀粉样肽的累积减少,达到预防和治疗老年痴呆性疾病和帕金森氏病的目的(Williams and Spencer, 2012)。

茶叶改善记忆的主要成分和作用机理是什么?日本和韩国的研究都表明,茶叶中的儿茶素类化合物如EGCG和茶叶中特有的茶氨酸(Theanine)都具有改善记忆和提高人脑认知功能(寺岛健彦等,2006,Lee 等,2012)。其作用机理主要有五个方面:

(1)抗氧化。日本的研究表明,人体长期摄入绿茶的儿茶素化合物后,一方面可以增进抗氧化酶类的活性,另一方面可以对ß-淀粉样肽的产生起抑制作用,同时提高海马神经的形成(Hashimoto et al., 2013)。

(2)通过血-脑屏障,与脑组织中铁离子的螯合作用。茶叶中的儿茶素EGCG业已证明可以通过血-脑屏障(Suganuga et al., 1998),并与铁离子螯合能力较强,能够减少患者体内ß-淀粉样肽水平以及延迟或阻止神经元的死亡(Reznichenko et al., 2006)。

(3)调控脑细胞生存和死亡的基因。低浓度的EGCG(<10μM)可以促进细胞死亡和前凋亡(proapoptotic)基因的表达,如bax,bad,caspase-1,caspase-6,cyclin-depenent kinase 抑制物 p-21和细胞周期抑制物gadd 45。

(4)调控与记忆功能相关的酶活性。如前所述,绿茶和红茶的提取物具有抑制乙酰胆碱酯酶和丁酰胆碱酯酶的活性,提高α-促分泌酶活性或抑制β-促分泌酶活性等作用,从而,消减ß-淀粉样肽在大脑中的积累及其毒性(Hashimoto et al.,2013)以及减轻老年痴呆症患者由ß-淀粉样肽诱导的认知能力降低的病理学症状(Giunta and Tan, 2013)。

(5)调节脑中的5-羟色胺(血清素)和多巴胺水平。茶氨酸能调节脑中的5-羟色胺(血清素)和多巴胺水平,具有改善脑的记忆学习和认知能力,减轻脑部的氧化性损伤(寺岛健彦等,2006)。

喝什么茶和喝多少茶可以改善记忆和预防神经退化性疾病呢?日本的一个包括1003名70岁以上的人群调查显示,每天饮绿茶2杯或2杯以上(每杯100ml)的日本老年人,认知受影响的风险比每周喝茶少于或等于1杯的人群低64%,每周喝绿茶4-6杯或每天1杯的人分别比不喝茶的人群低38%(Kuriyama et al., 2006)。美国的调查表明,每天饮茶2杯或2杯以上的人群发生帕金森氏病的危险性可降低28-60%(Checkoway et al., 2002)。另外,挪威、芬兰、新加坡等国的调查也表明,饮茶(红茶)可提高老年人的认知能力(Nurk et al., 2009);每天饮茶(红茶)3杯或3杯以上(每杯200ml)的人发生帕金森氏病的危险性较小 (Nurk et al, 2009,Tan et al., 2003)。 (作者系中国工程院院士、中国农业科学院茶叶研究所研究员)

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