Caffeine use in sports, pharmacokinetics in man, and cellular mechanisms of action.
Level 5 - mechanism / opinion, no new human data
Narrative review of pharmacokinetics and cellular mechanisms without systematic methodology
PubMed 16371327 · doi:10.1080/1040-830491379245
What was done
This narrative review synthesized evidence on caffeine use in sports, human pharmacokinetic parameters, and cellular mechanisms of action identified across in vitro and in vivo studies.
What was found
Caffeine is rapidly and completely absorbed in the gastrointestinal tract and distributed across all body tissues. Peak plasma concentrations reach approximately 50 microM, and elimination half-lives range from 2.5 to 10 hours. Hepatic microsomes metabolize caffeine into more than 25 derivatives, while less than 5% is excreted unchanged in urine. In vitro mechanisms include potentiation of muscle contractility through sarcoplasmic reticulum calcium release, phosphodiesterase inhibition, glycogen phosphorylase inhibition, sodium/potassium pump stimulation, phosphoinositide metabolism impairment, and non-selective adenosine receptor antagonism. Adenosine receptor blockade is identified as the primary physiologically relevant mechanism accounting for in vivo effects.
Why it matters
The paper outlines the pharmacokinetic profile and cellular actions of caffeine, clarifying the biological basis for its established role as an ergogenic aid in athletic performance.
Limits
As a narrative review, it lacks systematic search criteria, quality appraisal, and meta-analytic synthesis. The abstract provides no sample sizes or count of included studies. Several discussed biochemical actions derive from in vitro experiments that may not reflect physiological conditions in vivo.
Cited by
- supports It takes approximately 25 to 30 minutes for ingested caffeine to be absorbed and digested before it kicks in.