Caffeine Metabolism and Health Effects
Caffeine (1,3,7-trimethylxanthine) is the main psychoactive compound in coffee, acting as a stimulant of the central nervous system by means of antagonism to adenosine receptors. The metabolism of caffeine is reasonably well known. A number of studies have reported that after consumption and absorption (about 99%), caffeine is rapidly and extensively metabolized in humans. Caffeine metabolism in the liver is performed by phase I (citochrom P450) enzymes, mainly CYP1A2, which appears to be polymorphically distributed in human populations. Paraxanthine is the major caffeine metabolite in plasma, while methylated xanthines and methyluric acids are the main metabolites excreted in urine. In this chapter, the pharmacokinetics, metabolism and toxicology of caffeine and minor methylxanthines are discussed. Effects on health will also be approached.