維生素的性質

 

黃思賢醫學博士  著

收錄於【古今科學養生法】2006年5月初版

Mechanism of Vitamin

 

維生素執行許多不同的生化功能

維生素是有機營養素，需要量少，生化功能多，大多數機體不能合成，必須由食物提供。人每天僅需要毫克或微克級的維生素。維生素主要分成兩類：水溶性維生素和脂溶性維生素。

 

Vitamins Perform A Variety Of Biochemical Functions

Vitamins are organic nutrients that are required in smallquantities for many different biochemical functions, generallycannot be synthesized by the body, and must therefore be suppliedby the diet. Humans require either milligram or microgramquantities of each vitamin per day. Vitamins are classified intotwo main groups: water-soluble vitamins and lipid-solublevitamins.

 

水溶性維生素包括B族維生素（硫胺素、核黃素、尼克酸、泛酸、維生素B₆、生物素、維生素B₁₂和葉酸）和抗壞血酸（維生素C）。食物中的水溶性維生素經門靜脈吸收入血，其代謝產物經尿排泄，也有極少量游離維生素被貯存，絕大多數則需要經常由食物補充。葉酸可貯存在肝臟。幾個月不攝入維生素C或幾年不食維生素B₁₂會導致其缺乏。過量攝入一般可耐受，大劑量的尼克酸、維生素C、維生素B₁₂則發生副作用。

 

The water-soluble vitamins include the vitamin B complex(thiamin, riboflavin, niacin, pantothenic acid, vitaminB₆, biotin, vitamin B_12, and folic acid) andascorbic acid (vitamin C). Water-soluble vitamins are absorbed intothe hepatic portal vein, and any surplus of most of them isexcreted in the urine. There is thus little storage of the freevitamin, which in most instances needs to be continually suppliedin the diet. Some storage of folic acid occurs in the liver.Depletion may take several months for ascorbic acid and severalyears for B₁₂ (also stored in the liver). Excess intakeis generally well tolerated except for side effects occurring withlarge doses of niacin (in the form of nicotinic acid), ascorbicacid, or pyridoxine (vitamin B₆).

 

 

 

脂溶性維生素（維生素A、D、K、E）即存在於植物也存在於動物的脂類食物中，隨脂肪一起由小腸消化吸收，進入乳糜微粒，首先轉運到肝臟。維生素A、D、K主要貯存在肝臟，維生素E主要貯存在脂肪組織。脂溶性維生素不經尿排泄，故攝取過多會中毒（尤其是維生素A、D）。

 

The fat-soluble vitamins (vitamins A、D、E, and K), presentin food lipids of both plant and animal origin, are digested withfat and absorbed by the intestine and incorporated intochylomicrons. They are consequently transported mainly inchylomicron remnants, initially to the liver, which serves as amajor store of vitamins A, D and K. Adipose tissue is the majorstorage source of vitamin E. Fat-soluble vitamins are not excretedin the urine and, if taken in excess, are toxic(particularlyvitamins A and D).

 

某些疾病與輔助因數代謝有關，可用特異的維生素治療。因飲食中的食物缺乏維生素或其他原因（如吸收不良）引起的維生素不足，會導致缺乏綜合症。礦物質的重要性，在本書後面再討論。

 

Some diseases concerned with cofactor metabolism respond totreatment with specific vitamins.  Nonavailabilityof vitamins, whether due to dietary or other reasons (i.e. defectsin absorption), results in characteristic deficiency syndromes. Theimportance of minerals will be discussed about later in thebook.