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Millions of Americans use caffeinated beverages every day as a pick-me-up.
每天有上百萬的美國人使用含咖啡因的飲料來提神。
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It is, after all, the world's most popular drug.
這畢竟是全世界最流行的藥品。
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And with new caffeine infused products like energy drinks, gum, and even beef jerky hitting the shelves,
再加上新的含咖啡因產品如提神飲料、口香糖甚至是牛肉乾的上市，
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our love affair with caffeine shows absolutely no signs of slowing down.
我們對咖啡因的愛完全沒有要停下來的意思。
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Caffeine is an interesting drug because when it enters the body it breaks up into three different yet very similar molecules.
咖啡因是一個有趣的藥，因為當它進入體內的時候會分解成三種不同但結構相似的分子。
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When metabolized in the liver, enzymes chisel off one of three methyl groups to form these three metabolites with three different effects on your body:
被肝臟代謝時，酵素會切斷三個甲基中的一個甲基來形成這三種對身體會產生不同影響的代謝物：
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Theobromine, paraxanthine, and theophylline.
可可鹼、尿可可豆素以及茶鹼。
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While in the brain, this caffeine party crashes adenosine receptors, blocking the normal guest, adenosine, from doing its job.
當在腦部時，這些咖啡因產物會干擾腺苷受體，使原本的腺苷不能作用。
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Adenosine is responsible for slowing down nerve activity in your brains, giving us the cue to calm down and take a nap.
腺苷負責減緩我們腦中神經的活動量，讓我們知道應該要靜下來小睡一下了。
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Also, adenosine is responsible for regulating neurotransmitters in the brain such as dopamine.
腺苷也負責調控腦中的神經傳導物質，如多巴胺。
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As you can see, adenosine is also quite similar to caffeine in structure,
如你所見，腺苷和咖啡因的結構很類似，
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which is why caffeine binds so easily to the adenosine protein receptors.
也就是為什麼咖啡因可以很容易地和腺苷受體結合。
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Once connected, caffeine increases the activity in neurotransmitters like dopamine,
一旦結合後，咖啡因會增加像是多巴胺這類神經傳導物質的活性，
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ultimately leading to heightened brain activity.
最終讓腦袋更清醒。
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Then, the three metabolites perform their own specific functions.
然後，這三個代謝物都有自己特定的功能。
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Theobromine increases oxygen and nutrient flow to the brain.
可可鹼會增加腦中氧氣和養分的流量。
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Paraxanthine enhances your body's athletic performance by increasing the rate of fat breakdown to fuel muscle activity.
尿可可豆素藉由增加脂肪燃燒量來驅使肌肉活動增加，以強化你身體的肌肉效能。
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Theophylline increases your heart rate and reinforces your ability to concentrate.
茶鹼會加快心跳和加強你注意力集中的能力。
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And, although these effects come together to produce a state of wakefulness,
雖然這些效果加起來會讓我們更清醒，
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too much caffeine can turn sour pretty quick.
但太多咖啡因很快就會變成一件壞事。
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At higher doses, caffeine is known to cause jitters, anxiety, and just general all-around discomfort.
在高劑量的咖啡因下，會導致緊張、焦慮和全身性不適。
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For this reason, scientists have found that four hundred milligrams is the safest average dose of caffeine for adults.
因為這個原因，科學家發現 400 毫克的咖啡因對成人來說是最安全的平均劑量。
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To put that into perspective, that'll be around three eight-ounce cups of coffee,
更清楚地說，大約就是三杯8盎司的咖啡，
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five eight-ounce Red Bulls, or a whopping eight cups black tea.
五杯 8 盎司的 Red Bull，或是高達八杯的紅茶。
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And on a side note, scientists have also found that caffeine becomes toxic around 10 grams,
另外科學家也發現，當咖啡因的量到 10 克時會具毒性，
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which works out to be about seventy five cups of coffee, or 180 cups black tea.
大約等於是 75 杯咖啡或是 180 杯紅茶的量。
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However, the lethal limit does vary widely from person to person.
然而，致命的劑量會因人而異。
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Hey, thanks for watching folks.
嘿，謝謝大家的收看！
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Stay tuned next week, we've got more science coming your way that can only make you smarter.
下禮拜要繼續喔，我們還有準備更多科普知識，會讓你變得更聰明。
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And if you haven't already, make sure to subscribe, so that you don't miss anything.
如果你還沒訂閱，請記得訂閱，這樣你才不會錯過任何訊息。
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Oh, and if you have any chemistry themed questions, make sure you post them in the comments; they might be answered in upcoming videos.
對了，如果你有任何和化學相關的問題，記得在下面留言；接下來的影片可能會回答。
