Caffeine is also often used medically for both drowsiness and in a number of neonatal medicines.
Caffeine is a naturally occurring substance, being found in over 60 plants in the world. The most common are cacao pods (most commonly used for chocolate products), kola nuts (used for the preparation of cola drinks), the ilex plant (from whose leaves the popular south American beverage yerba mate is prepared), and in guarana seeds (an ingredient in some soft drinks). Due it being readily available, it is rarely artificially manufactured. However it may be made from a complicated mix of dimethyl urea and malonic acid.
The prevalence of caffeine is very different over the spectrum of beverages:
- An average cup of coffee (200ml) contains approximately 180mg of caffeine.
- Decaf coffee of the same volume on contains 2mg of caffeine.
- A cup of tea (200ml) contains about 80mg of caffeine.
- A bottle of coca cola (360ml) contains 64mg of caffeine.
- An average block of chocolate (50g) contains about 20mg of caffeine.
Humans have consumed caffeine since the Stone Age (chow p.19 – 20(Czech edition). It is known that the original consumption was by chewing the bark and leaves of certain plants.
In humans, there are four types of adenosine receptors. They all have different functions although they all overlap. They are named A1, A2A, A2b, and A3.
The functions of the first three are the most effected by the input of caffeine. The receptors are known to be throughout the entire body but the caffeine only has effect on the ones found in the brain. Caffeine also has a major increase on the amounts of the neurotransmitter, dopamine. This particular neurotransmitter is found throughout the brain but originate mainly in the hypothalamus, as well as in the substantia nigra pars compacta, and the ventral tegmental area which are both found in the mid brain.
The primary function of dopamine is in behaviour and cognition, motor activity, motivation and reward, sleep, mood, attention, and learning. The adenosine receptors play an important role in regulation the amount of dopamine produced.
Caffeine, when consumed, is believed to work by blocking adenosine receptors in the brain and other organs. The result is the reduced ability to slow down cellular activity. The resulted stimulated nerve cells produce adrenaline, which increases heart rate, increases blood flow to muscles, but decreases blood flow to the skin and organs. The blocked adenosine receptors also allow more production of dopamine which results in an elevated mood along with the usual symptoms of the intake of caffeine. Caffeine, however, only blocks out the first two types of adenosine receptors. A chemical called theophylline has effect on all four types. Theophylline is found in tea in small amounts along with caffeine so, although it is only slight, tea has a broader effect on the body.
