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Caffeine: how it works in the body

by Josephine Andrews
Published: Last Updated on 301 views

After getting up, first a coffee – for many people, nothing works in the morning without the daily boost of caffeine. The substance, which stimulates nerves and circulation, is consumed in a wide variety of forms: as tea, in chocolate or in energy drinks. But how much caffeine per day is considered safe? Read everything about the positive and negative effects of caffeine, the duration of the effect and the content of different foods here.

How does too much caffeine work?

Caffeine is part of everyday life for most adults and is very popular. The per capita consumption of coffee in Germany is now 168 liters per year. Caffeine is not only found in coffee and cola, but also in black or green tea – here we speak of theine – or cocoa. For many, however, it is not just about the taste, but about the invigorating effect. Caffeine is supposed to wake you up – and it does.

However, if you drink too many drinks with caffeine, this has a negative effect: migraine and headache attacks occur from an amount of around 5.3 mg/kg body weight. Other possible side effects are:

  • increased urination
  • incontinence (in men)
  • Stomach problems (increased gastric acid production)
  • Trouble falling asleep, insomnia
  • inner restlessness to the point of anxiety
  • sweats
  • cardiac arrhythmias
  • nervousness
  • irritability

What is caffeine?

Basically, caffeine is a psychoactive substance, an alkaloid that occurs naturally in various plants. Caffeine acts as a defense against pests in plants. It is contained, for example, in:

  • Guarana tree seeds
  • coffee beans
  • Kakaofrüchten
  • nuts of the cola tree
  • Leaves of tea bushes and mate plants

In humans, caffeine, which can also be produced synthetically, has a stimulating effect on the nervous system and increases concentration. This works even with small amounts of about 100 milligrams, i.e. about a cup of filter coffee. In this country, the brown bean brew is the main source of caffeine for adults.

What positive effects does caffeine have?

The most well-known effect of caffeine is that it helps to stay or become awake. It does this by docking onto the so-called adenosine receptors in nerve tissue and blocking them. The messenger substance adenosine regulates brain activity and acts as a tiredness signal.

A dose of 100 to 600 milligrams of caffeine also accelerates the ability to think, increases physical coordination and relaxes the bronchi.

In addition, caffeine constricts the blood vessels, including those of the head arteries, which widen in migraines, for example. The feeling of pain decreases. It also increases the concentration of neurotransmitters such as serotonin and dopamine in the brain . For these reasons, caffeine is also recommended as a remedy for migraines and headaches .

As for coffee itself, there is evidence that it may protect against type 2 diabetes, Parkinson’s disease, depression and liver disease. Coffee consumption also supports cognitive abilities in old age. In addition to caffeine, other substances contained in coffee are also responsible for this, for example antioxidants.

Caffeine: This is what happens in the body

But what happens in the body when it gets caffeine? Caffeine works by stimulating the release of the stress hormones cortisol and adrenaline. This increases blood pressure and the heart beats faster. It takes 15 to 30 minutes for the caffeine to get into the bloodstream and take effect. It then takes an average of four hours to be broken down and excreted from the body via the urine.

How strongly someone reacts to the substance depends, on the one hand, on how regularly they consume it. Caffeine has a habituation effect, the awakening effect then wears off. On the other hand, it is also crucial how sensitive someone reacts to caffeine and how quickly or slowly the metabolism removes the stimulant again.

Caffeine: recommended daily amount

For healthy adults, single doses of up to 200 milligrams (i.e. about 3 mg/kg body weight) and daily rations of up to 400 milligrams (5.7 mg/kg body weight) are considered harmless. For your orientation: A cup of filter coffee (200 ml) contains around 90 milligrams of caffeine. Negative effects may occur from a dose of 5.3 mg/kg body weight of caffeine. But that’s not an overdose.

Caffeine in children and the sick

It becomes harmful when children and sick people, for example with cardiac arrhythmias, take in too much caffeine – even in combination with some medications, little or no caffeine should be taken in. There is a risk of cardiovascular problems. For children and adolescents, the following values ​​apply as a limit for tea, cocoa and chocolate, depending on age: 0.2 (3-10 years) to 1.4 (10-18 years) milligrams per kilogram of body weight and day.

pregnancy and caffeine

Pregnant women also need to keep an eye on their caffeine consumption because caffeine penetrates the placenta unhindered. Caffeine affects the growth of the fetus because it doesn’t yet have the enzymes that break it down. According to the European Food Safety Authority, expectant mothers are therefore recommended not to drink more than 200 milligrams per day. That’s about two cups of coffee.

Athletes and caffeine

Athletes are also careful with the stimulant – at least during exercise. It is no longer on the list of banned substances. You do not consume more than one to two milligrams of caffeine per kilogram of body weight during competitions and training, otherwise there is a risk of dizziness and tachycardia, all the more likely if you are not used to caffeine.

Special case energy drinks and energy shots

Energy drinks, i.e. drinks containing caffeine, which often also contain taurine, glucuronolactone or inositol, and high-dose energy shots are popular pick-me-ups for young people, at work and for the party night.

If such a very high amount of caffeine is ingested, it is not uncommon for side effects to occur. However, moderate consumption of energy drinks is considered harmless. Pay attention to the consumption and consumer information. After all, a can only contains around 80 milligrams of caffeine – a little less than a cup of coffee.

A special feature is the combination with alcohol: the drink “Wodka Energy” is very popular with young people and young adults. In one evening, one person quickly consumes large amounts of more than a liter of energy drink. This age group therefore has an increased risk of diseases of the cardiovascular system. Serious cases with cardiac arrhythmias and kidney failure up to fatalities are known.

Food contains a lot of caffeine

In order to keep an eye on your consumption, it is good to know how much caffeine is in which foods. There are lists from specialist bodies such as the European Food Safety Authority (EFSA).

groceries caffeine content
Cappuccino Caffeine per cup (200 ml): 90 mg
Energy Drink Caffeine per can (250 ml): 80 mg
Espresso Caffeine per cup (60 ml): 80 mg
Mate Tee Caffeine per cup (200 ml): 80 mg
Black tea Caffeine per cup (200 ml): 45 mg
Cola Caffeine per can (330 ml): 35 mg
Green tea Caffeine per cup (200 ml): 30 mg
Cocoa Caffeine per cup (200 ml): 8-35 mg
chocolate Caffeine per half bar (50 g): 25 mg (dark); 10 mg (whole milk)


Caffeine: withdrawal symptoms

Caffeine is part of everyday life for many people – their body is used to the daily dose. Withdrawal may then be accompanied by withdrawal symptoms, as are also known from other addictive substances.

Possible symptoms are tiredness, exhaustion, nausea and, above all, headaches. The cause of the headache is an increased blood flow rate in the brain after stopping the caffeine. So if you want to reduce your consumption, it is better to gradually phase out the caffeine or, if necessary, accept a headache for a few days.

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