What are is the physiologic effects of caffeine consumption?

Updated: Jun 14, 2018
  • Author: Jasvinder Chawla, MD, MBA; Chief Editor: Nicholas Lorenzo, MD, CPE, MHCM, FAAPL  more...
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Caffeine, or 1,3,7-trimethylxanthine, is related structurally to uric acid. It is metabolized by demethylation and oxidation. The major human pathway results in paraxanthine (1,7-dimethylxanthine), leading to the principal urinary metabolites, L-methylxanthine, 1-methyluric acid, and an acetylated uracil derivative. Minor degradation pathways involve the formation and metabolism of theophylline and theobromine. No evidence exists to suggest that methylxanthines are converted to uric acid or that their ingestion can exacerbate gout.

The rate of elimination of methylxanthines varies from one individual to another, depending on both genetic and environmental factors, and 4-fold differences are not uncommon. In most cases, metabolism obeys first-order elimination kinetics within the therapeutic range. At higher concentrations, however, zero-order kinetics occur with the saturation of metabolic enzymes. This prolongs the decline of caffeine concentrations.

The metabolism of methylxanthines is also influenced by the presence of other agents or specific diseases. For example, cigarette smoking and oral contraceptives produce a small but appreciable increase in methylxanthine clearance. The half-life of theophylline can be prolonged significantly in patients with hepatic cirrhosis, congestive heart failure, or acute pulmonary congestion; values exceeding 60 hours have been reported.

Caffeine has a half-life in plasma of 3-7 hours; this increases approximately 2-fold in women who are in the later stages of pregnancy or are long-term users of oral contraceptive steroids.

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