How Caffeine Works, by Marshall Brain

Something like 90% of Americans consume caffeine in one form or another every single day. More than half of all American adults consume more than 300 milligrams (mg.) of caffeine every day, making it America's most popular drug by far. The caffeine comes in from things like coffee, tea, cola, chocolate, etc.
Have you ever wondered what it is that makes caffeine so popular? What does this drug do that causes its use to be so widespread? If you have ever wondered about the caffeine you consume, then this edition of How Stuff Works will enlighten you! It may also change, at least slightly, the way you think about this drug in your own life.

What is caffeine?
Caffeine is known medically as trimethylxanthine, and the chemical formula is C8H10N4O2 (see this page for an image of the molecular structure). When isolated in pure form, caffeine is a white crystalline powder that tastes very bitter. The chief source of pure caffeine is the process of decaffeinating coffee and tea.

Medically, caffeine is useful as a cardiac stimulant and also as a mild diuretic (it increases urine production). Recreationally, it is used to provide a "boost of energy" or a feeling of heightened alertness. It's often used to stay awake longer - college students and drivers use it to stay awake late into the night. Many people feel as though they "cannot function" in the morning without a cup of coffee to provide caffeine and the boost it gives them.

Caffeine is an addictive drug. Among its many actions, it operates using the same mechanisms that amphetamines, cocaine and heroin use to stimulate the brain. On a spectrum, caffeine's effects are more mild than amphetamines, cocaine and heroin, but it is manipulating the same channels and that is one of the things that gives caffeine its addictive qualities. If you feel like you cannot function without it and must consume it every day, then you are addicted to caffeine.

Caffeine in the diet
Caffeine occurs naturally in many plants, including coffee beans, tea leaves and cocoa nuts. It is therefore found in a wide range of food products. Caffeine is added artificially to many others, including a variety of beverages. Here are the most common sources of caffeine for Americans:

Typical drip-brewed coffee contains 100 mg per 6-ounce cup. If you are buying your coffee at Starbucks or a convenience store or drinking it at home or the office out of a mug or a commuter's cup, you are consuming it in 12, 14 or 20 ounce containers. You can calculate the number of milligrams based on your normal serving size.
Typical brewed tea contains 70 mg per 6-ounce cup.
Typical colas (Coke, Pepsi, Mountain Dew, etc.) contain 50 mg per 12-ounce can. Things like Jolt contain 70 mg per 12-ounce can.
Typical milk chocolate contains 6 mg per ounce.
Anacin contains 32 mg per tablet. No-doz contains 100 mg per tablet. Vivarin and Dexatrim contain 200 mg per tablet.
By looking at these numbers and by knowing how widespread coffee, tea and cola are in our society, you can see why half of all American adults consume more than 300 mg of caffeine per day. Two mugs of coffee or a mug of coffee and a couple of Cokes during the day are all you need to get you there. If you sit down and calculate your caffeine consumption during a typical day, you may be surprised! Many people consume a gram or more every single day and don't even realize it.

How caffeine works
Why do so many people consume so much caffeine? Why does caffeine wake you up? By understanding the drug's actions inside the body you can see why people use it so much.

In the HSW article entitled How Sleep Works, the action of adenosine was discussed. As adenosine is created in the brain, it binds to adenosine receptors. The binding of adenosine causes drowsiness by slowing down nerve cell activity. In the brain, adenosine binding also causes blood vessels to dilate (presumably to let more oxygen in during sleep).

To a nerve cell, caffeine looks like adenosine. Caffeine therefore binds to the adenosine receptor. However, it doesn't slow down the cell's activity like adenosine would. So the cell cannot "see" adenosine anymore because caffeine is taking up all the receptors adenosine binds to. So instead of slowing down because of the adenosine level, the cells speed up. You can see that caffeine also causes the brain's blood vessels to constrict, because it blocks adenosine's ability to open them up. This effect is why some headache medicines like Anacin contain caffeine - if you have a vascular headache, the caffeine will close down the blood vessels and relieve it.

So now you have increased neuron firing in the brain. The pituitary gland sees all of the activity and thinks some sort of emergency must be occurring, so it releases hormones that tell the adrenal glands to produce adrenaline (epinephrine). Adrenaline is, of course, the "fight or flight" hormone and it has a number of effects on your body:

Your pupils dilate
Your breathing tubes open up (this is why people suffering from severe asthma attacks are sometimes injected with epinephrine)
Your heart beats faster
Blood vessels on the surface constrict to slow blood flow from cuts and also to increase blood flow to muscles. Blood pressure rises.
Blood flow to the stomach slows
The liver releases sugar into the bloodstream for extra energy
Muscles tighten up ready for action
This explains why, after consuming a big cup of coffee, your hands get cold, your muscles tense up, you feel excited and you can feel your heart beat increasing.
Caffeine also increases dopamine levels in the same way that amphetamines do (heroine and cocaine also manipulate dopamine levels by slowing down the rate of dopamine re-uptake). Dopamine is a neurotransmitter that, in certain parts of the brain, activates the pleasure center. Obviously caffeine's effect is much lower than heroin's, but it is the same mechanism. It is suspected that the dopamine connection contributes to caffeine addiction.

So you can see why your body might like caffeine in the short term, especially if you are low on sleep and need to remain active. Caffeine blocks adenosine reception so you feel alert. It injects adrenaline into the system to give you a boost. And it manipulates dopamine production to make you feel good.

The problem with caffeine is the longer-term effects, which tend to spiral. For example, once the adrenaline wears off you face fatique and depression. So what are you going to do? You take more caffeine to get the adrenaline going again. As you might imagine, having your body in a state of emergency all day long isn't very healthy, and it also makes you jumpy and irritable.

The most important long-term problem is the effect that caffeine has on sleep. Adenosine reception is important to sleep, and especially to deep sleep. The half-life of caffeine in your body is about 6 hours. That means that if you consume a big cup of coffee with 200 mg of caffeine in it at 3:00 PM, then by 9:00 PM about 100 mg of that caffeine is still in your system. You may be able to fall asleep, but your body probably will miss out on the benefits of deep sleep. That deficit adds up fast. The next day you feel worse, so you need caffeine as soon as you get out of bed. The cycle continues day after day.

This is why 90% of Americans consume caffeine every day. Once you get in the cycle, you have to keep taking the drug. Even worse, if you try to stop taking caffeine, you get very tired and depressed and you get a terrible, splitting headache as blood vessels in the brain dilate. These negative effects force you to run back to caffeine even if you want to stop.

It has been said that the reason so many sodas and colas contain added caffeine is to get you hooked. In the same way that addiction to nicotine makes cigarettes such a great consumer product for the companies that produce cigarettes, added caffeine in colas causes addiction that boosts sales. It's not a pretty thought, but if you think about it you can see a pattern...

If you are interested in breaking the caffeine cycle in your own life, the book Caffeine Blues (especially Chapter 10) can be very helpful.

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