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(theguardian.com)

How much is too much caffeine?

a/Science & Technology by

Coffee is often a welcomed friend during the semester. According to folklore, the bean’s energizing properties were first discovered by an Ethiopian goat herdsman, who found his flock frolicking after eating coffee berries from nearby bushes. It’s not just goats that enjoy the effects of caffeine, however. According to the Food and Drug Administration (FDA), at least 80 per cent of adults in the U.S. consume various forms of the stimulant every day. But the caffeine addiction does not stop there—some proclaim their love of the chemical by displaying its structure on T-shirts, mugs, and laptop cases.

However, the five deaths linked to Monster Energy drinks and 13 linked to 5-Hour Energy shots in the U.S. last year,  according to FDA records and an interview with an agency official, suggest caffeine might not be such a nice friend. Bertil B. Fredholm, emeritus professor of pharmacology at the Karolinksa Institute in Sweden told Chemical & Engineering News (C&EN) that caffeine is a popular stimulant that triggers alertness in the body at low doses. Once absorbed by the bloodstream, the compound is metabolized in the liver, where it is transformed into three different primary metabolites (molecules produced during metabolism): paraxanthine, theophylline, and theobromine. Subsequently, these metabolites bind to two adenosine receptors, A1 and A2a, which are located throughout the body. These are proteins that regulate different physiological functions when activated by the neurochemical adenosine.

In normal circumstances, adenosine is produced by neurons—brain cells—throughout the day. The adenosine receptors are responsible for regulating nerve cell activity, and the release of neurotransmitters—brain chemicals that communicate information between the brain and body—such as dopamine. The interaction of the adenosine molecule with its receptors also promotes drowsiness. As adenosine binds to its  receptors to activate them, it slows down nerve cell activity, causing sleep.

However, when caffeine enters the bloodstream, the interaction of adenosine with its corresponding receptors is interrupted. Caffeine and its metabolites look like adenosine to nerve cells, but do not cause resulting response in receptors. Therefore, these metabolites bind instead to the adenosine receptors and prevent adenosine from doing its job. Consequently, dopamine and other neurotransmitter levels increase, resulting in a surge of nerve activity in the brain and on the heart. Furthermore, although caffeine looks like adenosine, it is not a neurochemical. Therefore, instead of slowing down the nerve cell’s activity, it speeds it up, causing you to feel more awake.

These effects might all seem harmless, but when taken in excessive quantities, caffeine can cause anxiety, irritation, and general mental discomfort. Importantly, caffeine can also have many negative physiological effects on the body, including increased blood pressure, rapid heart rate—and  in extreme cases, death.

Chances are, one cup of coffee is not going to kill you. The toxic level of caffeine in humans, about 10 g, is roughly equivalent to guzzling 75 cups of brewed coffee (in eight ounce mugs), or 120 cans of Red Bull over a few hours. However, this lethal limit is hardly a guideline. The tolerable amount of caffeine varies widely from person to person. Factors such as genetics, smoking, and age, all have an influence, although scientists are still unsure what exactly causes death by caffeine before the lethal limit.

Due to the variability in caffeine sensitivity among people, the FDA does not recommend a consumption limit for the entire population. However, the agency states on its website that 600 mg (four to seven cups of coffee) of caffeine is too much. While it is difficult to regulate the caffeine content of food and drink—since beverage manufacturers claim the compound is a necessary flavour enhancer for their products—the FDA puts a limit of 0.02 per cent (6 mg per oz) on the amount of the chemical allowed in cola-type beverages.

Unfortunately, beverage limitations do not apply to energy drinks, which are sold as dietary supplements. Drinks like 5-Hour Energy Shots may contain caffeine levels that exceed 6 mg per oz. Furthermore, beverage manufacturers often include caffeine as part of the “energy blend,” on the label. These contain multiple ingredients, none of which are broken down individually by milligrams. As a result, it is unclear how much of a contribution to the “energy blend” is made by energy-boosting compounds.

Despite the dangers of a caffeine overdose, it seems a caffeine craze has caught on in the marketing industry. Cracker Jack has switched out its caramel corn for Cracker Jack’d—two ounce packages of “power bites” jammed with 70mg of caffeine. It will join a market of many other caffeine-infused products, such as Water Joe—a bottle of water with the same amount of caffeine as a cup of coffee—caffeinated pancakes, and marshmallows.

While the marketing industry makes it easy to get caught up in the hype surrounding caffeinated food and beverages, everyone’s body metabolizes this chemical differently. While it is unlikely that a morning cup of coffee will do you any harm, it serves as an important reminder that there is no fixed threshold for the amount of caffeine your body can tolerate. With finals looming in the future, it might make more sense to swap out that 5-Hour Energy Shot for some sleep.

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