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咖啡因为何能振奋精神
Millions of Americans use caffeinated beverages every day as a pick me up.
数百万美国人每天都饮用咖啡因饮料来振作精神。
It is after all the world's most popular drug and with new caffeine infused products like energy drinks, gum and even beef jerky hitting the shelves,our love affair with caffeine shows absolutely no signs of slowing down.Caffeine is an interesting drug because when enters the body it breaks up into three different yet very similar molecules.
咖啡因毕竟是世界上最受欢迎的药物，而且现在还推出了加入咖啡因的产品，比如能量饮料，口香糖甚至牛肉干，我们与咖啡因的情缘没有任何减退的迹象。咖啡因是一种很有趣的药物，因为进入人体时它会分解成三种不同，但是非常相似的分子。
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:Theobromine. Paraxanthine. Theopylline.
在肝脏中新陈代谢的时候，酶凿掉三个甲基中的一个，形成对身体有着三种不同效果的三种代谢产物：可可碱，1，7-二甲基黄嘌呤和茶碱。
While in the brain, this caffeine party crashes adenosine receptors blocking the normal guest,adenosine from doing its job.
在大脑中的时候，这些咖啡因产物与腺甙受体碰撞，阻止正常的客体腺苷发生作用。
Adenosine is responsible for slowing down your back giving our brains giving us the cue to calm down and take a nap.
腺苷负责减缓背部向大脑发送平静下来，小睡一会儿的暗号。
Also adenosine is responsible for regulating neurotransmitters in the brain such as dopamine.
腺苷还负责调控大脑中的神经传递素，比如多巴胺。
As you can see, adenosine is also quite similar to caffeine in structure, which is why caffeine binds so easily to the adenosine protein receptors.
你可以看到，腺苷在结构方面与咖啡因非常相似，这也是咖啡因如此容易和腺苷蛋白质受体结合的原因。
Once connected, caffeine increases the activity in neurotransmitters like dopamine ultimately leading to heightened brain activity.
一旦结合，咖啡因会增加在多巴胺等神经传递素中的活动，最终导致大脑活动增加。
Then the three metabolites perform their own specific functions.
然后，三种代谢产物发挥自己的功能。
Theobromine increases oxygen and nutrient flow to the brain.
可可碱增加氧气和营养向大脑的流动。
Paraxanthine enhances your body's athletic performance by increasing the rate a fat breakdown to fuel muscle activity.
1，7-二甲基黄嘌呤加速脂肪的分解，为肌肉活动提供燃料，从而增强身体的运动表现。
Theopylline increase your heart rate and reinforces your ability to concentrate.
茶碱增强心率，让你更加集中精力。
And although these effects come together to produce a state of wakefulness,too much caffeine can turn sour pretty quick.
尽管所有这些效果结合起来会让你达到清醒状态，过多咖啡因很快就会让你的身体感到疲惫。
At higher doses caffeine is known to cause jitters, anxiety and just general all-around
discomfort.
过量咖啡会造成颤抖，焦虑和全身不适。
For this reason scientists have found four hundred milligrams is the safest average dose of caffeine for adults.
由于这个原因，科学家发现，对成年人来说，平均400毫克是最安全的剂量。
To put that into perspective, that'll be around three eight-ounce cups of coffee,five eight-ounce Red Bulls or a whopping eight cups black tea.
为了更好地理解，也就是大约3杯八盎司每杯的咖啡，5瓶八盎司每瓶的红牛和8杯红茶。
And on a side note site it’s also found that caffeine becomes toxic around 10 grams,which works out to be about seventy five cups of coffee, or 180 cups black tea.
另外，科学家还发现，当达到10克的时候，咖啡因就会产生毒害作用，也就是大约75杯咖啡，或者180杯红茶。
However, in the lethal limit does vary widely from person to person.
然而，致命量因人而异。
Hey thanks for watching folks.
感谢收看本期节目。
