Update on caffeine consumption, disposition and action
Introduction
To evaluate any possible toxic effects associated with caffeine, described in the following reports, it is desirable to have an indication as to the normal levels of exposure to caffeine from various sources. Coffee undoubtedly serves as the primary source of caffeine in the adult, but caffeine is also contained in tea and cocoa, many soft drinks and several drug preparations, including many over-the-counter products. Caffeine intake varies widely, since half the population does not drink coffee, and some individuals consume very substantial amounts. Therefore, knowledge of the range of caffeine consumption is helpful in evaluating the relevance of experimental studies intending to duplicate the human situation.
After its oral ingestion, caffeine is absorbed, is distributed to various tissues, and broken down to metabolites with variable pharmacological actions, which are then excreted. Pharmacokinetics describes these various processes as a function of time after caffeine intake, and may provide an explanation as to the duration and magnitude of biological effects observed. Caffeine is believed to interact with receptors for which adenosine is the normal substrate.
Investigators frequently have reported their observations on caffeine following the ingestion of coffee, under the assumption that any effect observed must be due to caffeine. However, there are several hundreds of other components in coffee, and it is vital to ascertain that these effects are indeed due to caffeine. Although caffeine probably is the most physiologically active ingredient of coffee, these other components can provide additional pharmacological effects. Obviously, this complication can be overcome by the administration of pure caffeine; however, this approach may be impractical. As decaffeinated coffee is extremely low in caffeine, a comparison with regular coffee could further substantiate that any observed effect is related to caffeine. However, the removal of caffeine from coffee may also lead to the extraction of other components with biological activity. The supplementation of decaffeinated coffee with an exact amount of caffeine is a more precise way of measuring the effects of caffeine (Denaro et al., 1990).
Section snippets
Caffeine content of caffeine in its most common sources
The preparations of coffee commonly used are anything but uniform. Coffees grown in different parts of the world differ genetically in their composition, so that the amount of caffeine per gram of bean will not be identical. There are numerous preparations of coffee, such as percolation, filtration, boiling, instant, espresso, etc., each of which will extract different amounts of caffeine per gram of coffee bean. The quantity of coffee beans employed, the degree of roasting, the fineness of
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