Caffeine in plants: effects, benefits and risks

Every coffee drinker knows caffeine, but it actually occurs in many plants. Here we look at where caffeine comes from, how it acts in the body and when it’s time to put the brakes on your cup.

Caffeine in plants: why does it matter?

Caffeine-containing plants are plentiful in nature, with the number of species reaching sixty. Coffee cherries, tea bush leaves, cocoa tree seeds, cola nut extract and sea squill bulbs are only part of the list. These plants don’t grow wild in Estonia, but caffeine-rich drinks are certainly consumed here.

Chemically, caffeine is a plant alkaloid. Alkaloids are nitrogen-containing plant compounds with a strong physiological effect on animal organisms, and more than two thousand of them are known today. For plants, these compounds are a kind of defense; for humans, they can be a medicine, a stimulant or a poison. The difference comes down to the amount and the situation.

Caffeine was first isolated as a plant alkaloid in 1819 by the German chemist F. Runge. The compound’s chemical structure was established in 1897 and is associated with the work of E. Fischer. Caffeine has the general formula C8H10N4O2 and is a white crystalline powder with a molecular weight of 194. Its melting point is 234236 oC. Caffeine dissolves poorly in cold water and much better in hot water.

Caffeine in drinks and in the body

Most people associate caffeine with coffee, but it is also found in tea, cocoa, cola drinks and energy drinks. A medium-sized cup of coffee contains 60140 mg of caffeine, depending on how it is prepared. A cup of tea provides about 2590 mg, a mug of cocoa 530 mg, a glass of cola 1030 mg, and an energy drink 1132 mg per 100 ml.

On the palate, we taste caffeine as bitterness. In the body, though, its effect is far stronger than a bitter aftertaste. Caffeine is absorbed quickly: within 45 minutes, 99% of it has been absorbed. About 20% is absorbed from the stomach and the rest from the small intestine. Caffeine concentrations between the blood and the brain even out in about 30 minutes.

The half-life of caffeine in the human body is 35 hours. This means that in that time roughly half of the caffeine that has entered the body is broken down. After consumption, caffeine has been found in saliva, bile, semen and breast milk. A small share, 0.54%, is excreted in urine unchanged. The remaining 96% is broken down in metabolism.

So what actually happens? Caffeine’s stimulating effect on the brain shows up quickly, within about 2040 minutes. It can raise alertness, shorten reaction time and help you overcome drowsiness. At the same time, caffeine doesn’t make anyone smarter. When the body is exhausted or stress runs deep, a large amount can have the opposite result: anxiety, restlessness and poor sleep.

How does caffeine affect the body?

At the cellular level, caffeine acts through adenosine receptors. This influences the synthesis of cyclic adenosine monophosphate, or cAMP. cAMP helps mobilize the body’s energy stores, such as the breakdown of glycogen, and boosts cellular metabolism.

At the organ level, the effects are easier to notice. Coffee can strengthen and speed up heart contractions, raise blood pressure, affect breathing and stimulate overall metabolism. Kidney activity also speeds up and sweating increases. That is why coffee is not the best thirst quencher in hot weather or after heavy fluid loss.

Caffeine dilates the blood vessels of skeletal muscles and may improve blood supply. At the same time, the blood vessels of many internal organs may actually narrow. This is why one person feels pleasantly clear-headed after coffee, while another gets heart palpitations.

Caffeine dependence doesn’t usually develop overnight. Even so, it is believed that around sixty percent of people who drink coffee every day have developed a caffeine dependence, and roughly eighty percent find it hard to stop enjoying coffee. The degree of dependence usually goes hand in hand with the amount of coffee drunk day after day.

Caffeine: who should be careful?

Caffeine can irritate the digestive tract, especially the stomach. It can trigger heartburn and pain. In ulcer disease, coffee and caffeine-rich drinks are contraindicated. Caution is also advisable for people predisposed to osteoporosis, that is, bone thinning caused by calcium loss. A moderate amount, no more than three cups a day, of coffee with cream does not usually cause osteoporosis.

People who have trouble falling asleep should avoid caffeine, especially in the evening hours. The same goes for those with heart disease or marked hyperexcitability. Large amounts of caffeine, 0.5 g and even more, can cause poisoning-like conditions. About ten grams can prove fatal, although it is not realistic to drink such a large amount through ordinary beverages.

Athletes should approach caffeine-containing products with a level head. If a competitor’s urine contained more caffeine than the permitted 12 mg/l, under IOC rules the athlete could risk disqualification. Athletes in some countries were warned not to drink more than 23 cups of coffee or tea right before competitions and doping tests.

Caffeine-rich drinks don’t belong on a child’s menu. A child’s nervous system is already easily excitable and tires quickly. Too much coffee can simply wear the body out.

Practical tips for consuming caffeine

• When you brew coffee, about 8590% of the caffeine in the ground coffee dissolves into the drink.
• With tea, about 7580% of the caffeine in the tea leaves makes it into the infusion.
• If you want a stimulating tea, let it steep for only 12 minutes. That gives the caffeine time to be released, while the tannins don’t yet bind much of it.
• For a more calming tea, let the leaves steep for 57 minutes. That gives the tannins more time to dissolve, and the effect of the caffeine is weaker.
• Keep in mind that you get caffeine from cola drinks, chocolate and cocoa too, not just from coffee.
• If you need a quick boost, black coffee without sugar hits harder than coffee with cream and sugar.
• Coffee grounds, sugar and cream weaken the effect of caffeine. Cream is especially effective, because in the stomach the curdled milk proteins bind the caffeine.
• The caffeine in tea usually acts more gently but for longer, because the tannins slow down absorption and breakdown.

Caffeine can also be found in cosmetic products, mainly skincare creams. Caffeine absorbed into the skin stimulates circulation, revs up the metabolism of fat cells and helps clear excess fluid and waste products. Still, it’s wise to take the promises with a grain of salt. A cream is no substitute for exercise, sleep or sensible nutrition.

FAQ: caffeine and everyday consumption

Does caffeine make me smarter?

No. Coffee can improve alertness, attention and reaction time, but it doesn’t add knowledge or replace rest.

Is caffeine good for quenching thirst?

Not when you’ve lost a lot of fluid. Caffeine may increase urine output and sweating, so water is the safer choice.

When should you avoid caffeine?

In the evening, if you have trouble falling asleep, if you have heart disease, during periods of strong anxiety, and if you have peptic ulcer disease, you should be very careful with caffeine.

Author: Marek Morozov

Source: WHO – physical activity.

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