I. Biochemistry
II. Effects

TABLE I Levels of Caffeine in Common Beverages and Foods
GLOSSARY
arrhythmia general term for irregularity or rapidity of the
heartbeat, an abnormal heart rhythm. cardiac output the volume of blood pumped by the ventricle
per unit time expressed in liters per minute; it is a function of
the stroke volume multiplied by the heart rate. heart failure failure of the heart to pump sufficient blood from
the chambers into the aorta; inadequate supply of blood
reaches organs and tissues.
CAFFEINE IS A PSYCHOACTIVE DRUG THAT OCCURS naturally in many foods and beverages including coffee, tea, chocolate, and cocoa. It has found its way into many commercial soft drinks because of its proven mild stimulant effect and relative safety when consumed in small amounts. But caffeine can produce beneficial effects in one individual and potentially harmful effects in another. Many pain relievers contain caffeine added to aspirin or acetaminophen to potentiate the effects of these agents. Levels of caffeine in common beverages and foods are shown in Table 1 and levels of caffeine in common drugs are listed in Table 2.
Caffeine is the most widely used psychoactive substance. More than 100 billion doses of caffeine are consumed annually in North America. Caffeine occurs naturally in more than 60 plant species worldwide, and the drinking of tea in China dates back to around 2500 BC.

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• I. BIOCHEMISTRY
  Caffeine is a xanthine derivative — 1, 3, 7-trimethyl-xanthine. Other naturally occurring xanthines include the well-known theophylline (the major constituent in tea) and theobromine. Coffee is a major source of caffeine and chlorogenic acid and also contains a substantial amount of magnesium and other micronutrients. Caffeine is a powerful central nervous stimulant and moderate doses of 200 mg contained in two cups of coffee activate the cerebral cortex sufficiently to slow changes in an individ¬ual’s electroencephalogram (EEG). Caffeine is also a mild cardiac stimulant.
• II. EFFECTS A. Cardiovascular
  Caffeine has mild and variable effects on the heart rate, the heart muscle, blood pressure, blood flow, and blood cholesterol.
• BIBLIOGRAPHY
  Blount, J. P., and Cox, W. M. Caffeine. Encyclopedia of Human Biology,