How It Works
Caffeine occurs naturally in the seeds, leaves, and fruits of different plants, such as coffee, tea, and cacao. Caffeine is structurally similar to adenosine, a neurotransmitter that tells us we're tired. The more adenosine in our nervous system, the more fatigued we feel. Caffeine actually bonds to our adenosine receptors, inhibiting the neurotransmitter's ability to bind there — thus tricking our bodies into feeling energetic.
How Much Do We Use?
How much caffeine are you actually consuming? It's hard to tell, partly because there is no standard cup of coffee or tea. A modest six-ounce cup of coffee might have some 70 milligrams of caffeine, while a Starbucks "grande" (16 ounces) packs 560 milligrams — as much as seven cans of Red Bull. And, different people feel the effects of caffeine differently, depending on both genetics and behavior. Women on birth control metabolize caffeine twice as slowly, which means they get double the jolt from the same cup of coffee. Meanwhile, smokers metabolize caffeine twice as fast as nonsmokers and so need twice the dosage to feel the same effect.
What happens when we consume more than the norm? About 1/16 of a teaspoon is a solid caffeine dose for a regular coffee drinker; a quarter teaspoon of caffeine will lead to unpleasantness. That can mean a racing heart, sweating, and acute anxiety. A tablespoon of caffeine? It'll kill you. Don't worry, though — that’s the equivalent of about 50 cups of coffee or 200 cups of tea. The danger of ODing on caffeine arises when you go straight to the hard stuff, in the form of powder or pills.
Surprisingly, the effects of caffeine also depend on an individual's personality: Extroverts get more cognitive enhancement from caffeine than introverts do. A 2013 study tested extroverts’ and introverts’ abilities to recall letters they had seen earlier and found that caffeine enhanced memory for the extroverts, but not for the introverts.
The Pause That Refreshes
Soda has been America’s favorite beverage since 1975, when it overtook coffee. Coca-Cola certainly leads the pack: If you put all the Coke ever produced into eight-ounce bottles and stacked them lengthwise, they would reach to the moon and back more than 2,000 times. Worldwide, people consume nearly 20,000 Coca-Cola beverages per second, or 1.7 billion a day. Most of the caffeine in modern sodas and energy drinks is not extracted from coffee or tea but is chemically synthesized in overseas labs.