For many, it keeps us awake and moving through our busy days.

對很多人來說，咖啡讓我們保持清醒，好讓我們在忙碌的日子中奔波。

But how does it work? What exactly does coffee do to your brain?

但原因是什麼呢？咖啡對你的大腦到底做了什麼事？

Whenever you're awake, a chemical called adenosine slowly accumulates in your brain.

當你清醒的時候，一個化學成分─腺苷 (adenosine) 會慢慢地累積在你的大腦中。

And this adenosine binds to receptors which slow down brain activity.

腺苷會和受體黏合來減緩腦部活動。

Ultimately, the more adenosine there is, the more tired your brain feels.

因此，腺苷越多，你的大腦就會越覺疲憊。

Which makes sense, as the longer you're awake, the more fatigued you become.

相當的，你清醒的時間越長，你越覺得疲憊。

Conversely, while you sleep, the concentration of adenosine declines, gradually promoting wakefulness.

相反的，當你睡覺時，腺苷的濃度會下降，漸漸讓你清醒。

But it turns out that the caffeine in your coffee is incredibly similar to adenosine in structure.

而其實，咖啡中的咖啡因結構與腺苷極為相似。

The caffeine works its way through your bloodstream and into your brain.

咖啡因是透過你的血液進入腦部。

Where it starts to compete and bind with adenosine receptors.

並開始與腺苷受體競爭、黏合。

But because it is not adenosine, the sleepiness effect isn't felt.

但因為它不是腺苷，所以我們不會有想睡的感覺。

Adenosine can no longer bind, meaning it's calming properties are diminished, which is great for you when you're feeling tired!

但因腺苷無法黏合，表示其平靜性能將縮減，這對於我們感到疲憊的時候是一件很棒的事情！

However, with long term use of caffeine, your brain responds by creating more adenosine receptors, which means more caffeine is required to elicit the same response.

但長期使用咖啡因，會讓我們的大腦製造更多腺苷來做為反應，這表示你需要更多的咖啡因來引出相同反應。

It also means that when you try to quit drinking coffee or miss your daily intake, you might experience some withdrawal symptoms and feel more tired than you would have before you ever drank coffee!

這也表示，當你嘗試著戒除咖啡，或減少每日攝取量，你可能會遇到一些戒斷症狀，且在你沒喝咖啡以前更感到疲憊！

But the caffeine doesn't stop there!

但咖啡因不只這樣！

It also stimulates the production of adrenaline.

他也會刺激腎上腺素的產生。

You know, the fight-or-flight hormone.

你懂得，那個「打」或「逃」的激素。

This increases your heart rate, gets your blood pumping, and even opens up your airways.

這會讓你心跳加速、血脈噴張，甚至打開你的呼吸道。

Furthermore, it affects Dopamine levels by preventing its reabsorption in the brain, which makes you feel happy!

此外，咖啡因還會影響多巴胺水平，防止其在大腦裡再吸收，讓你感到快樂！

In fact, this is the exact same thing that cocaine does, just to a lesser degree.

事實上，他的效應與古柯鹼一樣，只是較輕微而已。

It's a drug, after all!

它畢竟也算是種毒品！

This dopamine stimulation is also the aspect of coffee that makes it moderately addictive.

多巴胺刺激也是為什麼咖啡會讓人輕微上癮的原因。

So can you drink too much coffee?

所以，你可以喝過量的咖啡嗎？

It turns out there is a lethal dose of caffeine which is somewhere around 150 mg of caffeine per kilogram of our body.

原來，咖啡因有個致命劑量，即身體每公斤有 150 毫克的咖啡因。

This means if you weigh 70kg, you would require 14,000 mg of caffeine to overdose.

意思是如果你的體重為 70 公斤，那你需要 14,000 毫克才會咖啡因中毒。

Put into perspective, an average cup of coffee contains roughly 150mg of caffeine, meaning if you are 70kg, approximately 70 cups of coffee would kill you.

整體來說，一杯咖啡平均大約有 150 毫克的咖啡因，這表示如果你 70 公斤，約 70 杯咖啡會致命。

However, you'd have to drink those cups all at once making it effectively impossible to overdose on caffeine from coffee, since you wouldn't be able to physically fit that much in your stomach.

但前提是你必須一口氣全部喝下那些咖啡，這讓你幾乎無法因咖啡因過量而死亡，因為你的胃無法無法一次裝下這麼多東西。

You'd also start experiencing mania and hallucinations before getting to this point.

你也會在死亡前感受到躁狂與幻覺。

Caffeine also has a half life of around 6 hours.

此外，咖啡因也會有大約六小時的半衰期。

So if you drank a standard coffee with around 150mg of caffeine, after about 6 hours there will only be 75 mg left in your system and you'll be feeling half of the effect.

所以如果你喝了一杯大約有 150 毫克咖啡因的的咖啡，約六小時後，你的體內將只會剩下 75 毫克，讓你感受到一半的效果。

And 6 hours after that, you'll have 37.5 mg, leaving more room for adenosine to jump back into action.

再 6 小時候，體內只剩下 37.5 毫克，這讓腺苷有更多活躍空間。

Which is why you may reach for another cup throughout the day.

這是為什麼在一天中，你需要更多的咖啡。

To maintain that glorious, alert and energetic feeling.

來保持這種愉快、機敏、充滿活力的感覺。

So drink up! And enjoy the buzz while it lasts!

所以喝吧！享受咖啡因的好處......在他消失之前！

And for all of you in school, while we know caffeine is key, so are good deals on textbooks!

給所有就學的人，雖然我們知道咖啡因很重要，但教科書的優惠也很重要！

So we've teamed up with SlugBooks.com to get you the cheapest prices for the books you need.

我們與 SlugBooks.com 聯手來給你最便宜的教科書價格。

All you have to do is head to SlugBook.com/AsapSCIENCE and search the ISBN number of the books you're looking for.

你所需要做的，就是到 SlugBook.com/AsapSCIENCE 尋找你的 ISBN 書籍號碼。

SlugBooks will then compare prices from all across the net. Seriously, we know how expensive textbooks can be, so hopefully this will save you some money!

接著，SlugBooks 會幫你在網路上進行比價。說真的，我們知道教科書多貴，所以希望這可以幫你多省點錢。

Got a burning question you want it answered? Ask it in the comments or on Facebook and Twitter. And subscribe for more weekly science videos!

你有極想知道答案的問題嗎？請在下面留言，或是在臉書、推特上留言。