caffeine is a
methylxanthine present in tea and coffee, and therefore probably is the most common drug, regularly taken, in the world. Three very similar compounds — all in this same group of alkaloids — are present in common beverages, namely caffeine,
theophylline, and
theobromine. The first two are found mainly in tea and coffee, and the third in cocoa. Cola beans, used in the manufacture of well-known soft drinks, also contain caffeine. The three compounds differ very little from each other: simply the number and disposition of methyl groups about the xanthine nucleus is variable. Weight for weight, the caffeine content of coffee beans (0.7–1.5%) and tea leaves (2–3%) is similar, but generally a coffee infusion is stronger than that used for tea. Thus the dose of alkaloid per usual portion of tea or coffee is very similar, namely 50–150 mg, depending on taste.
Infusions made from the leaves of
Camellia sinensis (i.e. tea) have been consumed in the East for almost two millenia, and the practice reached Europe in the sixteenth century. The demand grew, and plantations were started in the Indian subcontinent. The British remain the most constant tea drinkers, with an average annual consumption of 4.5 kg, equivalent to a daily caffeine intake of 300 mg. In Japan tea is made from powdered green leaves. An elaborate tea ceremony is sometimes performed in which the tea maker performs a series of ritualized procedures in a very precise way. The green tea served at these ceremonies is usually bitter in taste.
Coffee cultivation began in the Yemen in the ninth century, the beans being obtained from a bush,
Coffea arabica, and they were introduced into Europe alongside tea in the sixteenth century. The major source of coffee is now in the state of Sao Paulo, Brazil. Coffee is supposed to have been discovered by an Ethiopian holy man whose goats had eaten the berries, allowing them to frisk all night long. It was claimed that coffee ‘quickens the spirits and makes the heart lightsome’ and is ‘good against the dropsy’, but a distinguished professor of medicine at Cambridge around 1900 claimed coffee caused
tremors and agitation. Explanations for all these claims can be made, particularly when allowance is made for ‘dose’. However, assuming the effects are due to caffeine, tea drinkers as well as coffee drinkers will benefit, or suffer, alike. While lethargy and irritability often result from withdrawal in drinkers, it is doubtful whether true caffeine dependency exists.
The pharmacological effects of caffeine are widespread and various. By inhibition of certain
enzymes, it allows an increase in the concentration of the ‘second messenger’, cyclic AMP, within cells, enhancing in turn the systems which this activates. Since caffeine penetrates the
blood–brain barrier it is assumed that the central stimulant effects that enhance alertness and counteract feelings of
fatigue, are due to this action. Caffeine also acts on the
kidneys as a mild diuretic; this combined with its stimulant actions on heart muscle provide good evidence for the claim that it is ‘good for the dropsy’, both by strengthening the force of the heart beat and by removing accumulated body fluid.
Alan W. Cuthbert
