Legend says that in 3000 B.C., the Chinese Emperor Shennong accidentally dropped a few leaves into boiling water and found the resulting drink to be restorative. He didn’t know it at the time, but those errant tea leaves started a world-wide love of energy drinks.

Today, one only needs to walk through a city block to understand our love affair with coffee, soda and caffeine in general. Caffeinated drinks are as ubiquitous as water.

Why does caffeine make you feel so good? Why is it so hard for many people to make it through the day without a cup of coffee? Let’s explore some of these questions to better understanding what caffeine does to our bodies — in particular, how it can affect sleep.

Caffeine and Your Brain

To understand why caffeine makes you feel awake, let’s take a journey deep into your brain. While your brain is awake, it is continuously producing a substance called adenosine. Adenosine arises from the breakdown of the energy molecule called adenosine triphosphate, or ATP.

Since the brain needs a great deal of energy, the adenosine keeps building up in your brain while you’re awake. Your brain constantly monitors how much adenosine is floating around, and the more adenosine it sees, the sleepier it feels.

Caffeine works by tricking your brain into thinking there is less adenosine present by inhibiting your brain’s ability to determine how much adenosine has built up. When you have caffeine in your system, your brain thinks it’s been awake for far shorter than it really has, so you feel more awake.

Unfortunately, caffeine doesn’t do anything to help get rid of adenosine in your brain. Only one thing can do that — sleep. Eventually, once the caffeine is out of your body, the sleepiness will return.

Caffeine: Good or Evil?

So, is caffeine good or bad for your health? It depends on the mode of delivery and timing.

Many studies report health benefits with coffee, such as decreased risk of diabetes, Parkinson’s disease and even some forms of cancer. But coffee is also a source of high levels of caffeine, which may cause sleep disruption and worsen underlying heart arrhythmias.

Sodas can provide caffeine, but typically also include unhealthy levels of sugar. Energy shots and other forms of high dose caffeine can be abused and cause serious health problems.

Just as important as mode of delivery is timing of caffeine use. Your body clears about half of the caffeine in your system every 4 to 7 hours.

Although most of the coffee from your day is out of your system by bedtime, some caffeine may still be present at night, even if you drink caffeine in the morning. For those that have difficulty sleeping, the ideal amount of caffeine is none.

If you drink to stave off the effects of a poor night’s rest with lots of caffeine spread throughout the day, you are doomed to have a poor night of sleep again, followed by a similar feeling of fatigue the next day. This can be a difficult cycle to break.

Remember that while caffeine can have its advantages, everything is best in moderation. No amount of caffeine can take the place of a great night’s sleep.