Caffeine in the body

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Absorption and metabolism of caffeine

Following oral consumption, caffeine is absorbed into the blood and body tissues and absorption is virtually complete about 45 minutes after ingestion. The peak plasma caffeine concentration is reached 15-120 minutes after ingestion. Caffeine has a half-life of approximately four hours1, although this timescale may be reduced or extended in certain groups of consumers. Smokers typically break down caffeine more quickly than non-smokers, while pregnancy tends to slow down the rate at which caffeine is broken down, particularly during the later stages. Elimination of caffeine from the body is accomplished mainly through metabolism in the liver and hence liver diseases might impact on the rate of caffeine elimination. This may also happen in individuals taking some medical treatments that are metabolized by the liver.

Genetic variation in absorption and metabolism of caffeine

Genetic variability can also impact on the effects of caffeine. The spontaneous consumption of caffeine is suggested to be influenced by a polymorphism of the adenosine A2A receptor5, the probability of having the ADORA2A 1083TT genotype decreases as habitual caffeine consumption increases, meaning there could be a biological basis for caffeine consumption behaviour and that individuals with this genotype may be less sensitive to the effects of caffeine. The metabolism of caffeine could be influenced by various expressions of the gene coding for the enzyme responsible for 95% of caffeine metabolism (cytochrome P450 1A2 isozyme). This variability could divide the population into slow and fast caffeine metabolizers6.

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