(Originally published by The Naked Scientists, January 23, 2015)
Apart from the buzz, what does caffeine actually do to us?
Do you consider yourself a drug addict? You just might be. There is a psychoactive drug that billions of people are addicted to, and it’s called caffeine. Coffee, tea, chocolate and energy drinks keep our planet buzzing. But do we really know what we are putting into our bodies, and what effects this might be having on us?
A brief history of caffeine:
Long before humans discovered its awakening and addicting powers, plants had been producing caffeine as a weapon against insect attack. The dose of caffeine in plant leaves is toxic to insects, keeping them from munching. When these leaves wilt and drop to the ground, caffeine spreads in the soil, hindering the growth of plants nearby. In addition to warding off insects and crippling plant peers, scientists found that plants are using their slightly caffeinated nectar to seduce bees. The ability to produce caffeine didn’t evolve just once; tea and chocolate both converged upon it separately, and recently it’s been discovered that coffee came upon it in a third evolutionary route. This shows caffeine is indeed a valuable commodity across many types of plant.
Then people enter the picture. Caffeine was discovered around five thousand years ago, simultaneously by the Chinese and the Native Americans. In China a legendary ruler called Shennong, the father of Chinese medicine, reputedly discovered it in tea. On the other side of the world, Native Americans drank it in their yaupon holly-based “black drink.”
As people around the world discovered caffeine in their native vegetation, various cultures concocted drinks or chewed on the plants’ leaves to experience its effects. More recently, caffeine is placed in a whole slew of products: energy drinks, pills and gels. These provide a wide range of caffeine concentrations ranging from just a few milligrams to over a hundred per ounce. Now caffeine is a multibillion-dollar global industry. 90% of the world consumes caffeine daily and in each of those billions of humans, caffeine spread itself throughout their bodies and enters their brains.
What does caffeine actually do to us?
Take a sip of your hypothetical cup of coffee. About 15-45 minutes after the caffeine has hit your stomach, it is absorbed by the small intestine. Depending on which form you consume it in, caffeine is absorbed at different speeds and with different efficiency. The fastest, most effective form of caffeine is liquid, like in tea or an energy drink. This form saturates the blood faster than a capsule and is more efficient (more caffeine actually makes it into your system) than gum. Once in your bloodstream, caffeine is quickly and evenly distributed throughout your body (heart, lungs, brain, breast milk, and even semen). The reason it distributed so quickly is because it is soluble in both fat and water.
As you’re sending sad glances to your empty mug, the caffeine in your body is being broken down by the blood-purification organ, your liver. If you are cramming for a test all night, you want that caffeine to be floating around in your body beyond the hour you spend procrastinating on Facebook. So how long does caffeine stick around in the body? The half-life of caffeine, or the time it takes of half of it to be broken down, is between five and six hours on average in adults. Pregnant women, women on oral birth control, and anyone who has alcohol in their system take longer to break down caffeine, whereas regular smokers feel the effects for a shorter time.
After failing to accomplish your task at hand in five hours, you pour yourself another steaming cup of Joe. Should you be worried about your health if this is your fourth cup of the day? An average eight fluid ounce cup of coffee contains between 65-120 mg of caffeine (although instant coffee has a much higher amount), an eight-ounce serving of brewed tea has 20-90 mg, and a 12-ounce can of fizzy drink has 30-60 mg. According to the FDA, a daily dose of 400 mg is safe, leaving anyone drinking four cups of coffee in the clear. But you may be surprised that 1 gram, or 10 cups, is toxic to the human body. And 10 grams (2 teaspoons) or 100 cups is lethal. Comparing that to cocaine, which is lethal at 1 gram, means cocaine is only 10 times more potent than caffeine!
As the caffeine gets broken down, what does it become? Pure caffeine is a powerfully bitter white powder. It is part of large group of naturally occurring compounds called alkaloids, which includes a handful of other popular hard drugs like psilocybin (shrooms) and lysergic acid diethylamide (LSD). Many alkaloids, such as atropine and quinine, are used for medical purposes. Within alkaloids, caffeine is a xanthine. Interestingly, xanthine has a similar in structure to two of four letters of the DNA alphabet. When the liver metabolizes caffeine, it either pulls off one of three dangling methyl groups (a carbon atom surrounded by three hydrogens), creating one of three new stimulants: theophylline, theobromine or paraxanthine, or it oxidizes caffeine into uric acid. To what degree and in what ways caffeine’s metabolites are responsible for its effects is unclear.
Caffeine jumps the fence that protects the brain, the blood brain barrier, as if it weren’t there. Caffeine is a sneaky con artist that resembles one of the signaling molecules in the brain: adenosine. Adenosine normally takes drowsiness messages between brain cells, but when caffeine is around, adenosine can no longer signal to the blocked adenosine receptors. In other words, caffeine doesn’t press the gas; it blocks the brake!.
Knowing this mechanism of action is fine and dandy, but it does not tell us which signaling systems this is disrupting in the brain. Blocking adenosine receptors means a downstream effect on many different neurotransmitters and this is important for caffeine’s ultimate effect on us. Researchers haven’t completely pieced together caffeine’s molecular effects, but the drug is purported to boost dopamine, adrenaline, acetylcholine, and serotonin.
So if caffeine is affecting the brain in so many ways, why isn’t caffeine powder being snorted alongside coke or shot alongside heroine? Caffeine does cause dependence, as the brain creates extra adenosine receptors. When you make a resolution to give up coffee, you feel extra drowsy because adenosine has more receptors to act on. Caffeine withdrawal kicks in, causing headaches, fatigue, irritability and other glorious symptoms.
In order to be considered a drug of abuse, caffeine also needs to cause clinical dependence. This is up for debate. Although caffeine encourages sustained use and causes positive subjective effects such as euphoria and energy, these are less pronounced than for drugs of abuse. Does caffeine create a compulsion and involvement that takes over peoples’ lives? Probably not. But does it have reinforcing and harmful effects on users? That’s less clear. Caffeine does also differ from hard drugs on a molecular level because it causes dopamine release in an area less crucial for addiction, making it less addictive. The newest version of the DSM, the American manual of mental disorders, does not include caffeine use disorder because, although caffeine causes withdrawal and “there is sufficient evidence to support this as a condition,” “it is not yet clear to what extent it is a clinically significant disorder.”
Now that you have some awareness of what caffeine is doing to your brain and body, try not to overdue your intake. On a societal level, perhaps we should emulate John Oliver’s #showusyourpeanuts and call for regulations that clearly label caffeine content.