甲硫氨酸

甲硫氨酸

甲硫氨酸的功能

甲硫氨酸是必需氨基酸之一，它不能由机体自身合成，必需从食物中获得。它提供硫和其他人体正常新陈代谢和生长所需的成分。甲硫氨酸也是一种防治脂肪肝的药物，可以帮助肝脏代谢脂肪。这类药物还包括胆碱、肌醇和甜菜碱。

患有艾滋病的人体内甲硫氨酸水平较低。许多研究者认为这可以解释这一疾病的一些症状，^{[1 2 3]}尤其是发生在神经系统的症状，包括痴呆^{[4 5]}。以前的一项试验证实服用甲硫氨酸（每天6克）可以改善艾滋病相关性神经系统退化导致的记忆减退。^[6]

其他一些试验也证实甲硫氨酸(每天5克)可以帮助治疗帕金森氏病。可是，另一形式的甲硫氨酸，腺苷甲硫氨酸会加重帕金森氏病，因此应该避免。^{[8 9 10 11 12]}在一项小样本量试验中发现，甲硫氨酸（每天2克）联合一些抗氧化剂可以减轻疼痛和胰腺炎的复发。^[13]

甲硫氨酸的分布

鱼类、肉类、豆类和乳制品含有丰富的甲硫氨酸。素食者可以通过食用谷类来获得甲硫氨酸，但豆类中甲硫氨酸含量较少。

甲硫氨酸认为与以下疾病有关（以下所有信息适用于个体化健康情况）：

哪些人可能会缺乏甲硫氨酸？

大多数人通过正常饮食可以获得足够的甲硫氨酸。在怀孕期摄入过低会导致新生儿神经管缺陷，但其机理还不清楚。^[14]

一般需要多少甲硫氨酸？

不同体重的人甲硫氨酸的需要量不同。可是，平均体重的成人每天大约需要800～1000毫克的甲硫氨酸，这在西方国家的日常饮食中很容易获得。

是否有副作用和药物相互作用？

动物试验证实在B族维生素缺乏的情况下，过多摄入甲硫氨酸会增加动脉粥样硬化的危险，因为它会增加血液中胆固醇和同型半胱氨酸的水平。^[15]这一现象还未在人类试验中得到证实。在摄入叶酸、维生素B6和维生素B12不足的情况下，过多摄入甲硫氨酸会增加甲硫氨酸向同型半胱氨酸（一种与心脏疾病和中风有关的物质）转化。试验证实大剂量服用甲硫氨酸（每天7克）会增加血液中同型半胱氨酸的水平。^[16]这一改变是否会引起明显的危害，目前在服用甲硫氨酸补充剂中还需进一步证实。每天服用2克甲硫氨酸补充剂维持较长时间还未见任何引起严重负反应的报道。^[17]

到目前为止，还不知道甲硫氨酸与其他药物间的相互作用。

参考文献

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