Route in the body
Within 45 minutes after consuming caffeine it enters the blood stream. Caffeine readily flows through the many available membranes, beginning in the mouth, throat, and stomach. After an hour caffeine reaches its peak concentration in the body, and typically after six hours it is excreted out of the body. Because caffeine has such as short half-life, and is not stored for later use; individuals typically reach for another source of caffeine two to three hours after their original cup or snack.
Caffeine is metabolized in the liver, producing three metabolites; Paraxanthine, Theobromine, and Theophylline.
Paraxanthine is the chief metabolite of caffeine. It has the same adenosine antagonistic effect that caffeine has in the brain. When binding to adenosine receptors, the metabolite directly raises blood pressure and epinephrine levels. Additionally, Paraxanthine promotes lipolysis, fat break down, directly increasing the amount of free fatty acids and glycerol in the blood, these compounds are used in the muscles for energy.
Theobromine is the metabolite that acts as a vasodilator and myocardial stimulator. This compound promotes artery dilation helping to maximize blood flow and nutrient delivery to cells which improves their function.
Theophylline is a common muscle relaxer, often prescribed to those with asthma to reduce constriction of airways. When consumed with caffeine this metabolite puts one at ease, and helps with concentration.
The consumption of too much caffeine can impact the effectiveness of these metabolites. As a tolerance is built for caffeine and its by-products the cycle of “caffeinism” begins and more caffeine is needed to reach a stimulated state.