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紐時摘譯:人體需要維他命 自己不會製造
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Depending on Vitamins Our Bodies Don’t Make
人體需要維他命 自己不會製造

By Carl Zimmer

In 1602, a Spanish fleet was sailing up the Pacific coast of Mexico when the crew became deathly ill. “The first symptom is pain in the whole body that makes it sensitive to touch,” wrote Antonio de la Ascensión, a priest on the expedition. “Purple spots begin to cover the body, especially from the waist down; then the gums become so swollen that the teeth cannot be brought together, and they can only drink, and finally they die all of a sudden, while talking.”
1602年,一支西班牙船隊沿著墨西哥的太平洋岸北上時,部分船員突然得到了會致命的疾病。隨隊教士亞桑森記錄道:「最初的症狀是碰不得的全身疼痛。全身開始出現紫色斑塊,尤其是腰部以下。接著牙齦腫大到牙齒無法咬合,導致生病的船員只能食用流質食物。最後,他們在講話時突然死亡。」

The crew was suffering from scurvy, a disease that was both familiar and mysterious. No one knew how to cure it. But Ascensión witnessed what he considered a miracle. While the crew was ashore burying the dead, one sick sailor picked up a cactus fruit to eat. He felt better. “They all began to eat them and bring them back on board so that, after another two weeks, they were all healed,” the priest wrote.
這些船員罹患人們既熟悉卻又不明所以的壞血病。沒有人知道如何治療。然而亞桑森親眼目睹他認為的一項奇蹟。船員上岸掩埋死者時,其中一名水手撿食一個仙人掌果實。他感覺好了些。亞桑森記錄道:「這些船員全都開始食用仙人掌果實,並將部分仙人掌果實帶到船上。兩個星期後,他們全部都痊癒了。」

It gradually became clear that scurvy was caused by a lack of fruits and vegetables. But it wasn’t until 1928 that the Hungarian biochemist Albert Szent-Gyorgyi discovered the ingredient that cured scurvy: vitamin C.
人們此後逐漸明白,壞血病是因為缺少蔬果所引起。然而直到1928年匈牙利生化學家森特喬治才發現,治癒壞血病的關鍵是維他命C

Szent-Gyorgyi’s experiments were part of a wave of early-20th-century research on vitamins. Scientists discovered that the human body required minuscule amounts of 13 organic molecules. A deficiency of any of the vitamins led to different diseases – a lack of vitamin A to blindness, vitamin B12 to severe anemia, vitamin D to rickets. But how did we end up dependent on these peculiar little molecules?
20世紀初出現了一波研究維他命的熱潮,森特喬治的實驗是其中之一。科學家發現,人體需要微量的13種有機分子。缺少其中任何一種都會引起不同的疾病:缺少維他命A會導致失明,缺少維他命B12會引起嚴重貧血,缺少維他命D則會引起軟骨病。然而我們又怎麼會變得必須依賴這些特定的微小分子呢?

It appears that vitamins were essential to life from its beginning some four billion years ago. Early life-forms could make their own vitamins, but some species later lost that ability. Species began to depend on each other for vitamins, creating a complex flow of molecules that scientists have named “vitamin traffic.”
打從大約40億年前生命開始形成起,維他命似乎就不可或缺。早期的生命形式或許可以自製維他命,然而部分物種後來失去了這種能力。不同物種開始相互仰賴以取得所需維他命,造就科學家稱為「維他命轉運(或傳遞)」的分子複雜流動。

Every vitamin is made by living cells. Vitamin D is produced in our skin, for example, when sunlight strikes a precursor of cholesterol. A lemon tree makes vitamin C out of glucose. While a protein may be made up of thousands of atoms, a vitamin may be made up of just a few dozen. And yet, despite their small size, vitamins expand our chemical versatility. A vitamin cooperates with proteins to help them carry out reactions they couldn’t manage on their own.
每種維他命皆由活體細胞製造。例如,陽光照射膽固醇的前驅物,我們的皮膚就會製造維他命D。檸檬樹會以葡萄糖製造維他命C。一個蛋白質分子可能由數千個原子組成,而一個維他命分子則可能只由數十個原子組成,維他命體積雖小,卻可擴大人體的化學多功能性。維他命會與蛋白質合作,幫助蛋白質完成自己辦不到的各種反應。

“If you talk about bacteria, fungi, plants, humans – everybody needs them,” said Harold B. White III, a biochemist at the University of Delaware.
德拉瓦大學生化學家懷特說:「舉凡細菌、菌類、植物、人類,個個都需要它。」

Once the ability to make vitamins evolved, some species became especially good at making them. Plants, for example, evolved into vitamin C factories, packing their leaves and fruits with the molecule. At first, vitamin C probably defended plants against stress – a function it carries out in other species.
製造維他命的能力開始演化之後,部分物種變得特別擅長製造維他命。以植物為例,它們最後演化為製造維他命C的工廠,並以這種分子填塞它們的葉子與果實。維他命C最初可能有助於植物對抗壓力。它目前在其他物種上發揮了這種功能。

Our own ancestors needed just thousands of years to alter their production of vitamin D. When humans left equatorial Africa and spread to higher latitudes, the sun was lower in the sky and supplied less ultraviolet light. By evolving lighter skin, Europeans and Asians were able to continue making a healthy supply of vitamin D.
我們自己的祖先只消幾千年就改變了他們製造維他命D的方法。人類祖先離開赤道非洲,向較高緯度地區遷徙時,太陽比較低,供應的紫外線比較少。歐洲人與亞洲人演化出比較淺色的皮膚,因而可以繼續製造足量的維他命D

Aside from vitamins D and K, we can’t make any of the vitamins we need to stay healthy. In some cases, our ancestors could make them, but lost that ability.
除維他命DK外,我們無法自行製造保持健康所需的其他維他命。在部分例子中,我們的祖先可以製造這些維他命,最後卻失去了這種能力。

Many vertebrates can make vitamin C. “We should be able to make it, too, since we have all the genes,” said Rebecca Stevens of the French National Institute for Agricultural Research. But we have mutations in one of those genes, known as GULO. Unable to make the GULO protein, we cannot produce vitamin C.
許多脊椎動物會自製維他命C。法國國立農業研究所的蕾貝卡史蒂芬說:「我們應該也可以自製維他命C,因為我們擁有必要的全部基因。」然而其中一個代號GULO的基因出現突變。我們因為無法製造GULO蛋白質而無法製造維他命C

“It’s not just us – it goes back a long time,” said Guy Drouin, a biologist at the University of Ottawa. Apes and monkeys also have disabled GULO genes. Dr. Drouin said the common ancestor we share with them lost the ability to make vitamin C around 60 million years ago.
渥太華大學生物學家德洛殷說:「不只是我們。這種現象由來已久。」猿猴也具有失能的GULO基因。德洛殷指出,我們與猿猴的共同祖先約於6000萬年前失去製造維他命C的能力。

Humans can’t make vitamin B12, either, so we need to get it from food. One way is to eat meat. It turns out that the animals that we consume don’t make B12 in their own cells. Instead, the bacteria in their guts manufacture it.
人類也無法自製維他命B12,必須從食物中攝取。食用肉類是方法之一。我們食用的動物自身細胞不會製造維他命B12。牠們腸內的細菌會製造。

We are also home to thousands of species of bacteria, which synthesize vitamins as they eat our food. Does that mean we depend on our internal vitamin traffic?
我們的體內有數千種細菌。它們食用我們的食物後,會合成多種維他命。這是否意味,我們仰賴自己體內的維他命轉運?

“It’s still theoretical,” said Douwe van Sinderen, of the University College Cork in Ireland. “But evidence is building that bacteria can provide some vitamins that we need.”
愛爾蘭科克大學的辛德倫說:「目前這還只是理論。然而有越來越多的證據顯示,細菌可提供我們需要的部分維他命。」

原文參照:
http://www.nytimes.com/2013/12/10/science/vitamins-old-old-edge.html

2014-01-21聯合報/G5/UNITEDDAILYNEWS 陳世欽 原文參見紐時週報十版左


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