一般的描述

幾乎所有的動物和植物綜合有像人類和少數的其他動物這樣的一些例外的他們自己的維他命 C., 包括, 猿，天竺鼠, 紅色發泄的夜鶯, 一個吃水果的蝙蝠和一個鱒魚的種。 這已經引導一些科學家, 包括保羅假定的林諾斯這些種或遺失了 (或者從不有了) 能力生產他們自己的維他命 C, 而且如果他們的飲食與對在確實綜合他們自己的維他命 C 的動物種被生產的數量的許多營養的比例項一起補充,較好的健康會產生。

維他命 C 首先在 1928 年被隔離，而且在 1932 年它被證明當避免壞血病的代理人。 艾伯特 Szent-Gy?rgyi 對于這一個壯舉在醫學被頒發 1937 諾貝爾獎。

維他命 C 是一種弱的酸, ascorbic 酸或含鹽的甜 ascorbate 叫做。 它是 L-ascorbic 酸的 enantiomer D-enantiomer 沒有表示生物學的活動。 兩者都是反映相同化學的分子結構的圖像表格, 見到光學的異構體).

物質的活躍部份是 ascorbate 離子, 能表達它本身如中立的或些微基本的一種酸或 ascorbate 的鹽。 商業的維他命 C 時常是一個 ascorbic 酸的混合, 鈉 ascorbate 及[或] 其他的 ascorbates 。 一些補充物部份地包含 D-enantiomer, 是無用的和無害處的。 為分子的化學特性的完全描述見到 ascorbic 酸文章。

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在身體中動作

如 hydroxylation 的一個叁加者，維他命 C 在連接著薄的紗織品中是對膠原蛋白的生產的需要。 這些纖維在身體各處是到處存在的,除了有柔性的結構之外提供公司。 一些薄的紗織品有膠原蛋白的較棒的百分比, 尤其: 剝皮, 黏液的薄膜，牙齒和 [硬]骨。

維他命 C 為神經系統或腎上腺的神經傳導物質， noradrenaline 和腎上腺素的綜合被需要。

維他命 C 也被需要綜合 carnitine, 重要的在能源的移動方面對細胞 mitochondria。

和最好的百分比的維他命 C 的薄紗織品 - 在血漿中的超過 100 次水平 - 腎上腺，垂體，胸腺，集成 luteum 和視網膜是。

腦，脾，肺，睪丸，淋巴結，肝，甲狀腺，小的腸黏膜，白血球，胰, 腎和唾液的腺通常有 10 到 50 在血漿中乘集中禮物。

維他命 C 是對于 ascorbate peroxidase 如一個基體的一個抗氧化物和行為。

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維他命 C 缺乏

沒有身體的器官儲存如一個主要的功能 ascorbate, 而且因此如果新鮮的補給沒被消耗過消化的系統，身體很快 ascorbate 耗盡它本身, 最后帶領如果維他命 C 的消費及時沒被重新開始，對即是壞血病 (一種維他命缺乏癥的形式) 的缺乏疾病，這造成疾病和死亡。

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敏銳的壞血病

敏銳的壞血病有:的特點

容易的打傷, 或以沒有明顯的因素打傷

釋放牙齒

表面出血

血管的脆弱

貧窮的痊愈

妥協處理免疫

溫和的貧血

對巨大的內在出血帶領, 壞血病最后致命, 而且是在水手之中的一種通常的情況和在冬天期間。 敏銳的壞血病在工業化的國家中現在非常稀有。

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每日的需求和劑量家眷效果

為在人類中維持最佳的健康有在維他命 C 的最好的劑量時間表 (數量和攝取的頻度) 上的科學群落里面的連續的辯論。[1]

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政府機關推薦攝取水平

沒有補充的一種均衡的飲食包含充足的維他命 C 在一個平均的健康成體中避免敏銳的壞血病。 因為吸煙的人, 那些在壓迫力之下, 和孕婦它些微地多拿。

對于維他命 C 攝取的忠告依下列各項已經被各種不同國家的代理商設定:

一天 40個毫克: 食物標準代理商 (英國)[2]

一天 60-95個毫克 , 飲食的叁考攝取 (DRI),推薦每日的津貼 (RDA) ，美國食物和營養董事會 2004[3] 。

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獨立的劑量忠告

一些科學家已經在下列的理由上批評政府機關劑量忠告。[引證需要]

他們不考慮個別的不同 , 像是年齡，重量, 等等舉例來說，較沈重的個體通常需要較多的維他命 C。

身材表現 , 數量需要避免敏銳形式的缺乏疾病, 當次臨床水平的時候疾病不是甚至公認。

數量需要避免其他的疾病不是考慮過的。

最佳的健康不是考慮, 因為健康的程度對準是那哪一個邊緣地比那哪一個被視為營養不良的好。

一些研究員已經計算數量對一個成人的人類需要達成如依下列各項綜合哺乳動物的維他命 C 的相似血清水平:

每一天 - 林諾斯的 Pauling 的每日推薦的 6000-18000個毫克

每一天 - 湯姆斯的征稅 6000-12000個毫克, 科羅拉多統合的醫生集中推薦。

在疾病或懷孕 (達 300g 對于一些疾病) 期間的一天 3000個毫克或更多 - 維他命 C 基金會的推薦。 [8]

一天 400個毫克 - 林諾斯保羅學會 & 美國國家衛生局 (NIH) 推薦。

從 3000個毫克到以被羅勃特 Cathcart 描述的一個記錄為基礎的一天 200,000個毫克 [即是擴大維他命 C 的劑量的維他命 C 流溢 wherin 的 4] 有，直到腹瀉發展, 然后選擇不引起腹瀉 (腸寬容閾值) 的最高的劑量. 高的劑量 (數以千計毫克) 可能造成腹瀉,如果劑量立刻被減少，這是無害處的。 一些研究員[4] 要求腹瀉的攻擊是身體的真實維他命 C 需求躺臥的地方指示。 兩者的 Cathcart[4] 和卡梅倫已經示范非常不舒服患有癌的病人或流行性感冒一點也不顯示任何對于腹瀉的證據直到 ascorbate 攝取到達水平高達 200 克 (? 強烈打擊).

然而，給維他命 C 的生物學的 halflife 相當短, 大約 30 分鐘在血漿中, 哪些 NIH 和 IM 研究員一種事實仍然沒有認識。 NIH 研究員建立 , 現在的 RDA 基于 , 測試在消費之后引導了 12 小時 (24個半的生命) 。 是鈍的 , 說機械， NIH 給予了被等候的一份維他命 C 的劑量直到它已經被排泄 , 然后測量了血[液] 水平 .[9]

為維他命 C(見到下面的擁護爭論) 的大劑量有一次強烈的擁護運動,雖然不是所有的謠傳利益被醫學建立支援。 許多贊成維他命的 C 組織促進很好超過現在的飲食叁考攝取 (DRI) 的用法水平。

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治療的申請和劑量

維他命 C 在飲食被需要避免壞血病,然而, 從當它以 1930 年代的純粹形式變成可得了的時候，一些開業者為壞血病之外的疾病以如治療的維他命 C 作實驗了。 大多數的著名人士在 Reidsville ，北卡羅萊那州中大體上是佛烈德 R. Klenner ，一位醫生練習。 他利用了口頭的和靜脈內的維他命 C 對待一個各類型的傳染和毒藥。他在 1949 年出版了一張紙 , 那描述了他如何已經見到對充分大的劑量維他命 C 的小兒麻痹癥生產量。

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心臟病

維他命 C 在為心臟病, 另外二存在含氨基的酸離氨酸和 nicotinic 酸 (一種維他命 B 3 的形式) 被請準專利治療的林諾斯 Pauling 是三種成分的主要部份。

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濾過性毒菌的疾病 , 和毒藥

當作為一個低成本和保險箱方法的時候， Orthomolecular 藥和科學意見的少數見到維他命 C 治療濾過性毒菌的疾病并且處理各類型的毒藥。

維他命 C 為在寒冷和感冒的治療中是有用的有增加的名譽,由于顯著生物化學家的它的推薦林諾斯保羅。 自從 Pauling 的流行書以后在數年中，有關維他命 C ，關于在健康和藥的大于維他命 C 的 RDA 數量的醫學主管當局的一般協議已經保持難懂。 Ascorbate 用法在研究決定于一些一天克, 然而, 已經與減少的寒冷期間和嚴重的癥狀有關, 可能地抗組織胺劑效果的結果 [10]. 最高的劑量治療,出版了被醫生提倡的特定 orthomolecular 治療政權的臨床結果。 Klenner(重復的 4 治療,400-700+ 毫克/公斤/日子 ) 和 Cathcart(對腸寬容的口試使用[4], 向上到 ~一天 150 克 ascorbate 對于感冒),已經實驗式地保持被傳統醫學的主管當局不演說長達數十年之久。

維他命 C 基礎每 20-30 分鐘推薦維他命 C 的達 8 克的開始用法 [13] 為了要在進步方面的寒冷傳染的癥狀上表示效果。表現簡直沒有效果的大部份的研究 ascorbate, 像是 100個毫克對藉著維他命 C 提倡者被視為 小的 的一天 500個毫克雇用劑量。 相等地重要地, 血漿高的劑量 ascorbate 的一半生活是大約 30 分鐘, 暗示大部分高的劑量研究已經方法有缺陷而且會被期望表示一種最小的利益。 分開劑量補充的臨床實驗,在藥理學理由上預測是有效的, 只有很少地沒有被在文學報告。 對于高劑量維他命 C 的本質上所有要求保持合乎科學地被駁倒。 維他命 C 的大的和時常發生劑量的臨床效力是一個開著的科學疑問。

在 2002 年 meta-在有傳染性疾病的治療中進入在 ascorbic 酸的效力方面的所有的被出版的研究之內學習和毒素被引導, 在～手邊湯姆斯征稅, 在丹佛的科羅拉多統合的醫生中心的醫學指導者。他要求證據為一個各類型的濾過性毒菌的傳染的它的治療角色存在而且對于蛇的治療咬。

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帶領中毒

也有證據那一粒維他命 C 是有用的在避免鉛中毒，可能地對螯狀來自身體的有毒的重金屬幫助方面。 [14]

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巨蟹座

在 2005 年在國家衛生局的 vitro 研究方面指出對癌細胞的一些菌株，被在藥理學集中 (也就是靜脈內的) 方面先取地管理的維他命 C 是有毒的。 作家注意: 這些調查結果把似有道理給癌治療的靜脈內的 ascorbic 酸, 而且有 H2 O2 可能是有益的對于傳染的治療的料想不到的含意 . 這一個研究似乎支援林諾斯 Pauling 的宣稱維他命 C 能用來對抗癌。[5]

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大瀑布

它也被建議維他命 C 可能避免大瀑布的形成。 [6]

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其他的效果

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禁止征候

給一個 25 歲男性的美國規定的食物叁考攝取可容忍的上面攝取水平 (UL) 是 2,000個毫克/日子。 維他命 C 被辨認出是為藥所知的最沒有有毒的物質之一。 給鼠的它的 LD50 是 11,900 毫克公斤-1[15],[16],[17].

主要的關心是人由于不尋常的或者向鐵超載情況,包括 hemochromatosis不演說。 維他命 C 提高鐵吸收。 如果鐵的受難者超載，情況帶 , 克按規定尺寸制作維他命 C 的劑量了, 他們由于可提高的鐵吸收可能使更壞 , 鐵超載。

不充分的葡萄糖 -6-磷酸鹽的 dehydrogenase 酵素 (G6 PD) 水平 , 一種遺傳基因的情況,可能使一些個體偏愛一些食物和藥物的特定氧物質禮物的攝取后的 hemolytic 貧血。 這包括重復的, 那里的維他命 C. 的非常大靜脈內的或者口頭藥量是 G6 PD 缺乏可用的一個測試 [18]. 高的劑量維他命 E 已經被計劃如一個潛在的給予保護的因素。

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副作用

如果接受量超過對個體的變數的一個界限，維他命 C 引起每個人的腹瀉。 Cathcart[4] 已經呼叫這限制腸寬容界限而且觀察它在患有重病的人中比那些健康良好者更高。 它在嚴重地生病的人中排范圍從在健康的個體一天 5 到 25 克到一天 300 克, 像是那些用愛滋病和癌。 雖然它可能是不便的，腹瀉副作用是無害處的。 腹瀉將會停止一旦劑量被減少就。

維他命 C 的大劑量可能引起酸的消化不良 (顛復的胃), 特別地當接受一個空的胃。 這個不愉快的但是無害處的副作用能被連同一餐一起藉由服用維他命避免, 或藉由彌補它的酸味藉由帶抗酸劑 , 像是碳酸氫鈉。

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聲稱的有害效果

維他命 C 的有害效果的報告容易接受全球的棒突起媒體。 同樣地，這些報告容易產生 , 很多的辯論和深入對維他命 C. 的較多研究在下面被描述的一些有害效果已經被證明在較遲的研究是無理由的而其他的效果仍然正在遭受較進一步的分析。

在 1998 年四月，日記自然報告維他命 C. 的過度劑量的聲稱致癌和產生畸形效果效果被在測試管實驗方面和在只有自由基的傷害 DNA 的 20個作記號的人中二個身上注意。 他們沒有被來自活的生物的較進一步的證據支援。 [7]

在 2000 年四月，南加州研究員的大學在帶高的維他命 C 劑量的人中報告脖子的動脈的一個使厚。 它稍后被這能被綜合對更厚和更強壯的動脈墻壁帶領的角色的維他命 C 的膠原蛋白解釋的維他命 C 提倡者指出了。 (裁判員。6個帕拉 10)

在 2004 年六月, 公爵大學研究員向 osteo 報告一種增加的感受性的事-在天竺鼠的關節炎然而喂了一種富含維他命 C. 的飲食, 一項 2003項研究在 Ume? 在瑞典的大學, 發現 維他命 C 的血漿水平, retinol 和尿的酸對被講到風濕性關節炎疾病活動的變數反的是有相互關系的 .

被深思的腎結石的增加危險可能是在大于常態數量 (>1 g) 中服用維他命 C 的副作用。行動的潛在機制透過維他命 C(ascorbic 酸) 的代謝對 dehydroascorbic 酸, 然后被使物質交替到醋漿草的酸[被需要的引證], 一個腎結石的已知成份。 然而，這一個議題仍然是爭論的, 藉由被呈現的證據為 [8] 和反對 [9] 這邊效果的可能性。 維他命 B 6 可能藉由減退草酸鹽生產鎮靜這危險 [10]. 另外地， thiamine 可能禁止草酸鹽形成。 此外, 改正任何的鎂缺乏 [11] 可能藉由減退草酸鹽結晶減少腎結石的危險。 增加一個流動的攝取也幫助到在腎中避免草酸鹽結晶。 有證據一個人的腸植物將會影響多少維他命 C 被轉換到草酸鹽。 病人用 predispostion 形成草酸鹽石頭或者或者那些在 hemodialysis 上應該避免維他命 C 的過度使用。

[12][13][14]

彈回壞血病 是理論上,不曾觀察, 可以發生的情況當維他命 C 的每日攝取從非常大的數量到相對低的數量快速地被減少的時候。提倡者建議這是發生的重捆效果的夸張因為 ascorbate-在攝取被降低, 而且用光沒有在被再補足的維他命 C 之后，依賴的酵素反應繼續 24-48 小時。 效果是對對短量的時間小于常態的較低的漿液維他命 C 血[液] 集中。 在這個時間的期間，透過減少的抵抗有寒冷或感冒傳染的微小危險。在一些天被停工的酵素反應和血清回返里面到正常水平的某人不采取大的補充物。 這不是下流, 哪一個拿零維他命 C 消費的數個星期生產癥狀。 它是某事服用大的維他命 C 的人補充需要知道為了要逐漸地減少藥量而不愿離開突然服用維他命 C。 (裁判員。6個帕拉 4) 這是那些動人的補充物的理論上的危險 - 舉例來說如果他們嚴重地有害地找他們自己, 和在沒有補充物的一所醫院中, 每次何時他們需要正常的或者比較好水平的維他命 C 對抗疾病 (裁判員。[4] 和尋找 主要的問題 ). 在這次，許多醫生和醫院職員不更加大約知道也不管理補充物的 megadosing, 所以病人可能必須仰賴朋友或者親戚帶給他們他們的補充物。

一些作家 [15] 已經識別來自維他命 C 的高劑量的貧窮銅吸收的理論上危險,雖然一點的實驗證據支援這。 然而， ceruloplasmin 水平明確地似乎被高的維他命 C 攝取降低。 在一項研究，維他命 C 的 600 毫克每日在年輕的男人中沒有減少銅吸收或者全部的身體銅狀態, 但是導致了與由銅缺乏所引起的那些類似的比較低度的 ceruloplasmin[16]. 在另外的, ceruloplasmin 水平重要地被減少 [17].

有能在懷孕的在 4 之下的女人數個星期中引誘一個流產的在維他命 C 的一天大約 12 克配的一些民間療法 proponants 之中流通的故事。 [18] 這然而不是被科學研究支援的。 [19]

最近的研究進入如可能的幫忙維他命 E 和 C 的使用之內在阻止氧化的壓迫力對前子間帶領方面仍然沒有表示任何的利益,[20] 但是確實增加被忍受一項研究的低 birthweight 的寶貝的比率。[21]

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維他命 C 的來源

維他命 C 被獲得過相當多世界的種群的飲食。 最富有的天然來源是水果和蔬菜, 和那些， camu camu 水果和 billygoat 李子包含維他命的最高集中。 它也存在于肉的一些削減, 尤其肝。 維他命 C 是那最廣泛地帶營養副食品和從平板和純粹的 ascorbic 酸水晶的飲料混合以多種表格是可得的在被膜中或如平原粉。

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種植來源

蘿絲臀部是一個維他命 CCitrus 水果 (橘色，檸檬，柚子, 石灰) ，蕃茄和馬鈴薯的特別地富有來源是維他命 C. 的好通常來源包括木瓜，綠花椰菜的維他命 C 的好來源的其他的食物, brussels 使發芽, 黑色的葡萄干，草莓，花椰菜，菠菜，香瓜， kiwifruit, 蔓越橘和紅色的胡椒粉。

當印度的醋栗樹, 是維他命 C 的最富有已知來源之一的時候， Emblica officinalis 時常提及 (新鮮果肉或缺少汁的達 900個毫克/100g 的 720個毫克/100g.)- 它包含 30 次在柳橙被發現的數量。

在植物起源的食物的維他命 C 的數量仰賴:

植物的精確變種,

土壤情況

它成長的氣候,

時間的長度自從它之后被挑選,

儲藏情況,

準備的方法。 在個別項目中煮時常被說破壞維他命 C- 但是在食物準備上見到派。

下列的桌形體是大約的而且在不同的生肉廠來源中表示親戚豐度。 數量被屈服水果或者蔬菜的每 100 miligrams 克。 (在比較中, 一茶匙純粹的維他命 C 秤重 4,500 miligrams)。。

植物來源數量

比利山羊李子 3150

Camu Camu 2800

Wolfberry 2500

蘿絲臀部 2000

Acerola 1600

Amla 720

Seabuckthorn 600

棗樹 500

寶貝樹 400

黑醋栗 200

紅色的胡椒粉 190

荷蘭芹 130

番石榴 100

Kiwifruit 90

綠花椰菜 90

大楊莓 80

Redcurrant 80

布魯塞爾使發芽 80

Lychee 70

柿子 60

木瓜 60

植物來源數量

草莓 60

橘色 50

檸檬 40

甜瓜, 香瓜 40

花椰菜 40

柚子 30

懸鉤子 30

橘子 30

過于文雅的橘色 30

強烈的感情水果 30

菠菜 30

卷心菜生的綠色 30

以石灰處理 20

芒果 20

甜瓜, honeydew 20

蕃茄 10

越橘 10

鳳梨 10

Pawpaw 10

葡萄 10

種植酸的

維生素C又叫抗壞血酸，是一種水溶性維生素。在所有維生素中，維生素C是最不穩定的。在貯藏，加工和烹調時，容易被破壞。它還易被氧化和分解。

一、維生素C主要生理功能

1、 促進骨膠原的生物合成。利于組織創傷口的更快愈合；

2、 促進氨基酸中酪氨酸和色氨酸的代謝，延長肌體壽命。

3、 改善鐵、鈣和葉酸的利用。

4、 改善脂肪和類脂特別是膽固醇的代謝，預防心血管病。

5、 促進牙齒和骨骼的生長，防止牙床出血。；

6、 增強肌體對外界環境的抗應激能力和免疫力。

二、維生素C缺乏和疾病

維生素C缺乏時，其癥狀表現為：

1． 牙齦腫脹出血，牙床潰爛、牙齒松動。

2． 骨骼畸形、易骨折。

3． 傷口難愈合等。進一步則引起壞血癥、貧血。

4． 大出血和心臟衰竭，嚴重時有猝死的危險。

5． 肌肉纖維衰退，包括心肌衰退。

維生素C是無毒的營養素，但每天攝入量超過八克會有害，癥狀包括：惡心，腹部痙攣，腹瀉，鐵的過量吸收，紅血球破壞，骨骼礦物質代謝增強，防礙抗凝劑的治療，血漿膽固醇升高，并可能對大劑量維生素C形成依賴。

三、維生素C主要食物來源有哪些？

獼猴桃、櫻桃、柑橘類水果、番石榴、青椒或紅辣椒、西紅柿、芥菜、菠菜、草莓、卷心菜、土豆、葡萄以及番茄等.

藥物作用

維生素C在體內參與多種反應，如參與氧化還原過程，在生物氧化和還原作用以及細胞呼吸中起重要作用。從組織水平看，維生素C的主要作用是與細胞間質的合成有關。包括膠原，牙和骨的基質，以及毛細血管內皮細胞間的接合物。因此，當維生素C缺乏所引起的壞血病時，伴有膠原合成缺陷，表現為創傷通難以愈合，牙齒形成障礙和毛細血管破損引起大量瘀血點，瘀血點融合形成瘀斑。

General description

Almost all animals and plants synthesize their own vitamin C. There are some exceptions, such as humans and a small number of other animals, including, apes, guinea pigs, the red-vented bulbul, a fruit-eating bat and a species of trout. This has led some scientists, including Linus Pauling to hypothesize that these species either lost (or never had) the ability to produce their own Vitamin C, and that if their diets were supplemented with an amount of the nutrient proportional to the amount produced in animal species that do synthesize their own Vitamin C, better health would result.

Vitamin C was first isolated in 1928, and in 1932 it was proved to be the agent which prevents scurvy. Albert Szent-Gy?rgyi was awarded the 1937 Nobel Prize in Medicine for this feat.

Vitamin C is a weak acid, called ascorbic acid or a salt ascorbate. It is the L-enantiomer of ascorbic acid The D-enantiomer shows no biological activity. Both are mirror image forms of the same chemical molecular structure, see optical isomers).

The active part of the substance is the ascorbate ion, which can express itself as either an acid or a salt of ascorbate that is neutral or slightly basic. Commercial vitamin C is often a mix of ascorbic acid, sodium ascorbate and/or other ascorbates. Some supplements contain in part the D-enantiomer, which is useless and harmless. See the ascorbic acid article for a full description of the molecule's chemical properties.

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Functions in the body

As a participant in hydroxylation, vitamin C is needed for the production of collagen in the connective tissue. These fibers are ubiquitous throughout the body, providing firm but flexible structure. Some tissues have a greater percentage of collagen, especially: skin, mucous membranes, teeth and bones.

Vitamin C is required for synthesis of dopamine, noradrenaline and adrenaline in the nervous system or in the adrenal glands.

Vitamin C is also needed to synthesize carnitine, important in the transfer of energy to the cell mitochondria.

The tissues with greatest percentage of vitamin C — over 100 times the level in blood plasma — are the adrenal glands, pituitary, thymus, corpus luteum, and retina.

The brain, spleen, lung, testicle, lymph nodes, liver, thyroid, small intestinal mucosa, leukocytes, pancreas, kidney and salivary glands usually have 10 to 50 times the concentration present in plasma.

Vitamin C is an antioxidant and acts as a substrate for ascorbate peroxidase.

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Vitamin C deficiency

No bodily organ stores ascorbate as a primary function, and so the body soon depletes itself of ascorbate if fresh supplies are not consumed through the digestive system, eventually leading to the deficiency disease known as scurvy (a form of avitaminosis), which results in illness and death if consumption of vitamin C is not resumed in time.

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Acute scurvy

Acute scurvy is characterized by:

easy bruising, or bruising with no apparent cause

loose teeth

superficial bleeding

fragility of blood vessels

poor healing

compromised immunity

mild anemia

Leading to massive internal hemorrhaging, scurvy is eventually fatal, and was a common condition among sailors and during winter. Acute scurvy is now very rare in industrialized countries.

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Daily requirements and dose dependant effects

There is continuing debate within the scientific community over the best dose schedule (the amount and frequency of intake) of Vitamin C for maintaining optimal health in humans.[1]

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Government agency recommended intake levels

A balanced diet without supplementation contains enough Vitamin C to prevent acute scurvy in an average healthy adult. For people who smoke, those under stress, and pregnant women it takes slightly more.

Recommendations for vitamin C intake have been set by various national agencies as follows:

40 mg per day: Food Standards Agency (UK) [2]

60–95 mg per day, Dietary Reference Intake (DRI), Recommended Daily Allowance (RDA), U.S. Food and Nutrition Board 2004 [3].

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Independent dose recommendations

Some scientists have criticised governmental agency dose recommendations on the following grounds.[citation needed]

They don't take into account individual differences such as age, weight, etc. For example, heavier individuals generally need more vitamin C.

The figures represent the amount needed to prevent the acute form of deficiency disease, while subclinical levels of the disease are not even acknowledged.

The amount needed to prevent other diseases is not considered.

Optimal health is not a consideration, as the level of health targeted is that which is marginally better than that which is considered malnourished.

Some researchers have calculated the amount needed for an adult human to achieve similar blood serum levels as Vitamin C synthesising mammals as follows:

6000-18000 mg per day – Linus Pauling's daily recommendation

6000-12000 mg per day – Thomas Levy, Colorado Integrative Medical Centre recommendation.

3000 mg per day or more during illness or pregnancy (up to 300g for some illnesses) – Vitamin C Foundation's recommendation. [8]

400 mg per day – Linus Pauling Institute & US National Institutes of Health (NIH) Recommendation.

from 3000 mg to 200,000 mg per day based on a protocol described by Robert Cathcart [4] known as a vitamin C flush wherin escalating doses of Vitamin C are given until diarrhea develops, then choosing the highest dose that does not cause diarrhea (bowel tolerance threshold). High doses (thousands of mg) may result in diarrhea, which is harmless if the dose is reduced immediately. Some researchers[4] claim the onset of diarrhea to be an indication of where the body’s true vitamin C requirement lies. Both Cathcart[4] and Cameron have demonstrated that very sick patients with cancer or influenza do not display any evidence of diarrhea at all until ascorbate intake reaches levels as high as 200 grams (? pound).

However, the biological halflife for vitamin C is quite short, about 30 minutes in blood plasma, a fact which NIH and IM researchers have failed to recognize. NIH researchers established the current RDA based upon tests conducted 12 hours (24 half lives) after consumption. To be blunt, says Hickey, the NIH gave a dose of vitamin C, waited until it had been excreted, and then measured blood levels.[9]

There is a strong advocacy movement for large doses of Vitamin C (see Advocacy arguments below), although not all purported benefits are supported by the medical establishment. Many pro-Vitamin C organizations promote usage levels well beyond the current Dietary Reference Intake (DRI).

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Therapeutic applications and doses

Vitamin C is needed in the diet to prevent scurvy, however, from the time it became available in pure form in the 1930s, some practitioners experimented with vitamin C as a treatment for diseases other than scurvy. Most notable was Fred R. Klenner, a doctor in general practice in Reidsville, North Carolina. He utilized both oral and intravenous vitamin C to treat a wide range of infections and poisons. He published a paper in 1949 that described how he had seen poliomyelitis yield to vitamin C in sufficiently large doses.

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Heart disease

Vitamin C is the main of the three ingredients in Linus Pauling's patented cure for heart disease, the other two being the amino acid lysine and nicotinic acid (a form of Vitamin B3).

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Viral diseases, and poisons

Orthomolecular medicine and a minority of scientific opinion sees vitamin C as being a low cost and safe way to treat viral disease and to deal with a wide range of poisons.

Vitamin C has a growing reputation for being useful in the treatment of colds and flu, owing to its recommendation by prominent biochemist Linus Pauling. In the years since Pauling's popular books about vitamin C, general agreement by medical authorities about larger than RDA amounts of vitamin C in health and medicine has remained elusive. Ascorbate usage in studies of up to several grams per day, however, have been associated with decreased cold duration and severity of symptoms, possibly as a result of an antihistamine effect [10]. The highest dose treatments, published clinical results of specific orthomolecular therapy regimes pioneered by Drs. Klenner (repeated IV treatments, 400-700+ mg/kg/day [11][12]) and Cathcart (oral use to bowel tolerance[4], up to ~150 grams ascorbate per day for flu), have remained experimentally unaddressed by conventional medical authorities for decades.

The Vitamin C Foundation recommends an initial usage of up to 8 grams of vitamin C every 20-30 minutes [13] in order to show an effect on the symptoms of a cold infection that is in progress. Most of the studies showing little or no effect employ doses of ascorbate such as 100 mg to 500 mg per day, considered small by vitamin C advocates. Equally importantly, the plasma half life of high dose ascorbate is approximately 30 minutes, which implies that most high dose studies have been methodologically defective and would be expected to show a minimum benefit. Clinical studies of divided dose supplementation, predicted on pharmacological grounds to be effective, have only rarely been reported in the literature. Essentially all the claims for high dose vitamin C remain to be scientifically refuted. The clinical effectiveness of large and frequent doses of vitamin C is an open scientific question.

In 2002 a meta-study into all the published research on effectiveness of ascorbic acid in the treatment of infectious disease and toxins was conducted, by Thomas Levy, Medical Director of the Colorado Integrative Medical Centre in Denver. He claimed that evidence exists for its therapeutic role in a wide range of viral infections and for the treatment of snake bites.

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Lead poisoning

There is also evidence that Vitamin C is useful in preventing lead poisoning, possibly helping to chelate the toxic heavy metal from the body. [14]

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Cancer

In 2005 in vitro research by the National Institutes of Health indicated that Vitamin C administered in pharmacological concentrations (i.e. intravenous) was preferentially toxic to several strains of cancer cells. The authors noted: These findings give plausibility to intravenous ascorbic acid in cancer treatment, and have unexpected implications for treatment of infections where H2O2 may be beneficial. This research appeared to support Linus Pauling's claims that Vitamin C can be used to fight cancer.[5]

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Cataracts

It has been also suggested that Vitamin C might prevent the formation of cataracts. [6]

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Other effects

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Contraindications

The U.S. Dietary Reference Intake Tolerable Upper Intake Level (UL) for a 25-year old male is 2,000 mg/day. Vitamin C is recognized to be one of the least toxic substances known to medicine. Its LD50 for rats is 11,900 mg kg-1 [15], [16], [17].

A primary concern is people with unusual or unaddressed iron overload conditions, including hemochromatosis. Vitamin C enhances iron absorption. If sufferers of iron overload conditions take gram sized doses of Vitamin C, they may worsen the iron overload due to enhanced iron absorption.

Inadequate Glucose-6-phosphate dehydrogenase enzyme (G6PD) levels, a genetic condition, may predispose some individuals to hemolytic anemia after intake of specific oxidizing substances present in some food and drugs. This includes repeated, very large intravenous or oral dosages of vitamin C. There is a test available for G6PD deficiency [18]. High dose Vitamin E has been proposed as a potential protective factor.

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Side-effects

Vitamin C causes diarrhea in everyone if taken in quantities beyond a limit which is variable to the individual. Cathcart[4] has called this limit the Bowel Tolerance Limit and observed that it is higher in people with serious illness than those in good health. It ranges from 5 to 25 grams per day in healthy individuals to 300 grams per day in the seriously ill persons, such as those with AIDS and cancer. The diarrhea side-effect is harmless though it can be inconvenient. The diarrhea will cease as soon as the dose is reduced.

Large doses of vitamin C may cause acid indigestion (stomach upset), particularly when taken on an empty stomach. This unpleasant but harmless side-effect can be avoided by taking the vitamin along with meals, or by offsetting its acidity by taking an antacid such as baking soda.

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Alleged harmful effects

Reports of harmful effects of vitamin C tend to receive great prominence in the world's media. As such, these reports tend to generate much debate and more research into Vitamin C. Some of the harmful effects described below have been proven to be unfounded in later studies, while other effects are still undergoing further analysis.

In April 1998 the journal Nature reported alleged carcinogenic and teratogenic effects of excessive doses of vitamin C. The effects were noted in test tube experiments and on only two of the 20 markers of free radical damage to DNA. They have not been supported by further evidence from living organisms. [7]

In April 2000, University of Southern California researchers reported a thickening of the arteries of the neck in persons taking high vitamin C doses. It was later pointed out by vitamin C advocates that this can be explained by vitamin C's collagen synthesising role leading to thicker and stronger artery walls. (ref.6 para 10)

In June 2004, Duke University researchers reported an increased susceptibility to osteo-arthritis in guinea pigs fed a diet high in vitamin C. However, a 2003 study at Ume? University in Sweden, found that the plasma levels of vitamin C, retinol and uric acid were inversely correlated to variables related to rheumatoid arthritis disease activity.

A speculated increased risk of kidney stones may be a side effect of taking Vitamin C in larger than normal amounts (>1g). The potential mechanism of action is through the metabolism of Vitamin C (ascorbic acid) to dehydroascorbic acid, which is then metabolized to oxalic acid[citation needed], a known constituent of kidney stones. However, this issue is still controversial, with evidence being presented for [8] and against [9] the possibility of this side effect. Vitamin B6 may mitigate this risk by decreasing oxalate production [10]. Additionally, thiamine may inhibit oxalate formation. Furthermore, correcting any magnesium deficiency [11] may decrease the risk of kidney stones by decreasing oxalate crystallization. Increasing one's fluid intake also helps to preventing oxalate crystallization in the kidney. There is evidence that a person's intestinal flora will influence how much vitamin C is converted to oxalate. Patients with a predispostion to form oxalate stones or or those on hemodialysis should avoid excess use of vitamin C.

[12][13][14]

Rebound scurvy is a theoretical, never observed, condition that could occur when daily intake of Vitamin C is rapidly reduced from a very large amount to a relatively low amount. Advocates suggest this is an exaggeration of the rebound effect which occurs because ascorbate-dependent enzyme reactions continue for 24-48 hours after intake is lowered, and use up vitamin C which is not being replenished. The effect is to lower one's serum vitamin C blood concentration to less than normal for a short amount of time. During this period of time there is a slight risk of cold or flu infection through reduced resistance. Within a couple of days the enzyme reactions shut down and blood serum returns to the normal level of someone not taking large supplements. This is not scurvy, which takes weeks of zero vitamin C consumption to produce symptoms. It is something people who take large vitamin C supplements need to be aware of in order to gradually reduce dosage rather than quit taking Vitamin C suddenly. (ref.6 para 4) This is a theoretical risk for those taking supplements - e.g. if they find themselves severely ill, and in a hospital without the supplements, at a time when they need normal or better levels of vitamin C to fight the disease (ref.[4] and search for The major problem). At this time, many doctors and hospital staff do not know much about nor administer megadosing of supplements, so that patients may have to rely on friends or relatives to bring them their supplements.

Some writers [15] have identified a theoretical risk of poor Copper absorption from high doses of Vitamin C, although little experimental evidence supports this. However, ceruloplasmin levels seem specifically lowered by high vitamin C intake. In one study, 600 milligrams of Vitamin C daily did not decrease copper absorption or overall body copper status in young men, but led to lower ceruloplasmin levels similar to those caused by copper deficiency [16]. In another, ceruloplasmin levels were significantly reduced [17].

There are stories circulating among some folk remedy proponants that doses of around 12 grams per day of Vitamin C can induce an abortion in women under 4 weeks of pregnancy. [18] This is not supported by scientific research however. [19]

Recent studies into the use of both Vitamin E and C as possible help in preventing oxidative stress leading to pre-eclampsia has failed to show any benefit,[20] but did increase the rate of babies born with a low birthweight in one study.[21]

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Sources of vitamin C

Vitamin C is obtained through the diet by the vast majority of the world's population. The richest natural sources are fruits and vegetables, and of those, the camu camu fruit and the billygoat plum contain the highest concentration of the vitamin. It is also present in some cuts of meat, especially liver. Vitamin C is the most widely taken nutritional supplement and is available in a variety of forms from tablets and drink mixes to pure ascorbic acid crystals in capsules or as plain powder.

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Plant sources

Rose hips are a particularly rich source of vitamin CCitrus fruits (orange, lemon, grapefruit, lime), tomatoes, and potatoes are good common sources of vitamin C. Other foods that are good sources of vitamin C include papaya, broccoli, brussels sprouts, black currants, strawberries, cauliflower, spinach, cantaloupe, kiwifruit, cranberries and red peppers.

Emblica officinalis often referred to as Indian gooseberry, is one of the richest known sources of vitamin C (720 mg/100g of fresh pulp or up to 900 mg/100g of pressed juice.)– it contains 30 times the amount found in oranges.

The amount of vitamin C in foods of plant origin depends on:

the precise variety of the plant,

the soil condition

the climate in which it grew,

the length of time since it was picked,

the storage conditions,

the method of preparation. Cooking in particular is often said to destroy vitamin C - but see the section on Food preparation.

The following table is approximate and shows the relative abundance in different raw plant sources. The amount is given in miligrams per 100 grams of fruit or vegetable (in comparison, one teaspoon of pure vitamin C weighs 4,500 miligrams)...

Plant source Amount

Billy Goat plum 3150

Camu Camu 2800

Wolfberry 2500

Rose hip 2000

Acerola 1600

Amla 720

Seabuckthorn 600

Jujube 500

Baobab 400

Blackcurrant 200

Red pepper 190

Parsley 130

Guava 100

Kiwifruit 90

Broccoli 90

Loganberry 80

Redcurrant 80

Brussels sprouts 80

Lychee 70

Persimmon 60

Papaya 60

Plant source Amount

Strawberry 60

Orange 50

Lemon 40

Melon, cantaloupe 40

Cauliflower 40

Grapefruit 30

Raspberry 30

Tangerine 30

Mandarin orange 30

Passion fruit 30

Spinach 30

Cabbage raw green 30

Lime 20

Mango 20

Melon, honeydew 20

Tomato 10

Blueberry 10

Pineapple 10

Pawpaw 10

Grape 10

Plant sour

維生素C基本知識

維生素C又叫L-抗壞血酸，是一種水溶性維生素，能夠治療壞血病并且具有酸性，所以稱作抗壞血酸。在檸檬汁、綠色植物及番茄中含量很高。抗壞血酸是單斜片晶或針晶，容易被氧化而生成脫氫壞血酸，脫氫壞血酸仍具有維生素C的作用。在堿性溶液中，脫氫壞血酸分子中的內酯環容易被水解成二酮古洛酸。維生素C可輔助治療多種疾病，維生素C不僅能預防和減輕感冒癥狀，還能增強免疫力預防心臟病發生。

維生素C（Vitamin

C

，Ascorbic

Acid）又叫L-抗壞血酸，是一種水溶性維生素。食物中的維生素C被人體小腸上段吸收。一旦吸收，就分布到體內所有的水溶性結構中，正常成人體內的維生素C代謝活性池中約有1500mg維生素C，最高儲存峰值為3000mg維生素C。正常情況下，維生素C絕大部分在體內經代謝分解成草酸或與硫酸結合生成抗壞血酸-2-硫酸由尿排出；另一部分可直接由尿排出體外。一、維生素C主要生理功能1、

促進骨膠原的生物合成。利于組織創傷口的更快愈合；2、

促進氨基酸中酪氨酸和色氨酸的代謝

標簽：維生素有關資料