咖啡因究竟對你的身體做了什麼

Is marijuana now the most widely used psychoactive substance? Nope. And it's not alcohol or nicotine, either. It's actually caffeine, that little gem lurking in your morning cup of coffee. Caffeine is known to be a stimulant; people use it most often to get a little boost of energy. But exactly what is happening in your body when you consume caffeine, either in coffee, tea, or energy drinks, or in foods like chocolate, hasn't been totally figured out yet.

現在大麻是不是被普遍用作精神刺激物質呢？答案是否定的。酒精和尼古丁也不是。實際上，答案是咖啡因，那個潛伏在清晨咖啡中的小精華。衆所周知，咖啡因是一種興奮劑；人們喝咖啡經常是爲了讓自己更精神。但當你攝入咖啡因（不管是在咖啡、茶、能量飲料還是在巧克力等食物中）時，人們還未完全明白當時你的身體究竟在發生什麼。

Researchers currently think that the caffeine buzz has something to do with the inhibitory neurotransmitter adenosine. When adenosine receptors are normally activated, they tend to cause sedative effects, such as reducing your heart rate and suppressing the release of other neurotransmitters (including glutamate and dopamine).

目前，研究員們認爲咖啡因陶醉感與抑制性神經遞質腺苷有關。當腺苷受體被正常激活時，它們往往會引起鎮靜作用，比如降低心率和抑制其它神經遞質（包括穀氨酸和多巴胺）的釋放。

But caffeine may work by binding to (and blocking) adenosine receptors in your brain and throughout your body. And once those adenosine receptors are blocked, the other neurotransmitters excite your system. Caffeine messes with our daily rhythms in other ways, too.

但咖啡因可以通過與大腦和整個身體內的腺苷受體結合而起作用。一旦腺苷受體被阻，其它的神經遞質就會使人體系統興奮。咖啡因也會以其它的方式打亂我們的日常節奏。

For one, it affects the way our bodies release cortisol, commonly known as the "stress hormone." Caffeine actually causes a pretty solid increase in cortisol levels in those who aren't normally coffee-drinkers. But in those who enjoy their daily caffeinated beverages - and have thus built up at least a partial tolerance to the chemical - the effects are a little less clear.

一方面，咖啡因影響着身體釋放俗稱爲"應激激素"的皮質醇的方式。實際上，對於那些不經常喝咖啡的人來說，咖啡因會導致他們的皮質醇水平顯著升高。但對於那些每天都喜歡來點含咖啡因飲料的人說--因此他們對這種物質至少已經有了一定的耐受性--咖啡因的影響就不那麼清楚了。

But we do know they last for a long time. Even cutting off your caffeine six hours before bedtime may not be enough to ensure you doze off easily. And that's important because those aforementioned adenosine receptors also play a role in keeping our circadian rhythms humming along. So, if you're a regular coffee-drinker, you might want to be extra careful about sticking to your routine. An ill-timed coffee break or - even worse - a skipped one, could make it hard to get back into your normal sleep-wake cycle.

但我們清楚咖啡因會持續很長一段時間。即使在睡前六小時不喝咖啡也不能確保你能快速入睡。因爲上述的腺苷受體也在保持我們的晝夜作息正常方面起着一定的作用，因此這一點是很重要的。所以，如果你經常喝咖啡，那在堅持自己的日常習慣方面，你要額外注意哦。在不合時宜的時間喝咖啡--或更糟--直接不喝，都會讓你在重回正常的睡眠週期方面變得困難。

On top of all that, we know that different people react to coffee (and its caffeine) differently. While it is pretty much a requirement for some, others complain that it makes them far too jittery to get anything done. And researchers are now learning that difference may depend at least partly on your genes.

除此之外，我們知道不同人對咖啡（和其咖啡因）的反應不同。雖然，對於有些人來說，咖啡是必備的，但有些人卻抱怨咖啡使他們過度緊張，搞得什麼事都做不成。研究員們目前得知這個差異可能取決於人們的基因。