Ask a Scientist

Courtesy of The University of Tennessee, Knoxville.

If you’re like me, a cup or two of coffee in the morning is customary, comforting, but also outright necessary to get a day started. 

Perhaps, also like me, there was once a deadline or an urgent need for wakefulness that drove you to overdo the caffeine, causing the jittery, shakey, heart-fluttering sensation of 6+ cups of coffee drunk in far too short a period of time (my excuse: exams).

So why is there a point where more caffeine doesn’t give us more of the effects we want? The simple reason for why more isn’t better is that caffeine, in many ways, acts like a drug.

The U.S. Food and Drug Administration (FDA) does not officially classify caffeine itself as a drug (unless you’re consuming caffeine in a pill form), but does require that foods containing it be labelled. They also discourage children, adolescents and pregnant women from consuming caffeine. And there are fairly good reasons for this.

To summarize, caffeine acts as an adenosine receptor antagonist, which means it blocks receptors in your brain that bind to a substance (adenosine) which causes you to feel sleepy. Since caffeine binds to nerve cells where adenosine would, nerve cell firing ramps up instead. All this hubbub in your brain makes your pituitary gland notice; to combat what it perceives as a weird emergency stimulus, the pituitary produces adrenaline.

If you’ve ever been startled and felt that kind of jolt like sensation through your body - that’s adrenaline. Biologically, adrenaline stimulates a litany of nifty effects that culminate in the wide-awake feeling caffeine gives: rapid heart rate, sugar released into the blood from your liver for energy, tightening muscles, and more. This neural stimulation may have negative effects on developing brains like in the case of children or pregnant women. However, in general, adults drinking caffeine moderately suffer little or not at all and gain alertness and small improvements of energy.

There are a few other buzz-worthy effects of caffeine that may entice you to drink more. Caffeine can literally make you feel happy because, like cocaine, it alters dopamine reabsorption, a neurotransmitter popularly associated with pleasure. Also like cocaine, caffeine can be addictive: abruptly ceasing regular caffeine consumption can result in headaches, anxiety and nervousness. Moderate consumption of caffeine (~400 mg) results in that temporary rush of pleasant energy, but taking too much caffeine (>400 mg) can ramp up these effects so they become markedly negative. Here are some of the potential side-effects if you take in too much caffeine: insomnia, nausea, headache, rapid heart rate and interestingly, a sense of unease or feeling of unhappiness, sometimes called dysphoria.

These effects are not fully understood, but likely stem from an overstimulated nervous system producing anxiety and dysphoria in some individuals, combined with negative effects of exhaustion resulting from adrenaline overstimulating the body. Feeling tired and depressed after the caffeine leaves your system is common, as the activity it incites takes up energy. If you really overdose and take (an estimated) 1200 mg of caffeine in a single sitting, outcomes like seizures and death can result.

Good news though: it’s extremely uncommon to die from caffeine. The average amount of caffeine in a standard eight-ounce cup of coffee is around 100 mg. To overdose on caffeine, you’d have to chug twelve cups, or three-quarters of a gallon, in a single sitting. Are you at risk? Unlikely.

Knowing that, if you’re drinking a reasonable amount of caffeine, it can have some notable benefits. What qualifies as reasonable? Well, the FDA’s dietary guidelines recommend up to 400 milligrams of caffeine a day, roughly equivalent to 4 cups of coffee.

This threshold varies for each individual, but on average, if you drink about that much per day as an adult, caffeine can actually provide benefits. There are links between (moderate) caffeine consumption and good health, including potentially lower risk of diabetes and Parkinson’s disease. Like most things, however, you should consume caffeine in moderation because too much can seriously kill your buzz.

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