In a healthy person, caffeine promotes cognitive arousal and fights fatigue. These same activating properties can produce symptomatic distress in a small subset of the population. It pharmacologically stimulates the CNS, the heart, voluntary muscles, and gastric acid secretion and induces diuresis. Caffeine is rapidly absorbed. Peak plasma levels are achieved in about 1 hour.
Caffeine saturates all body tissues and fluids, including breast milk.
The amount of caffeine in coffee and tea varies based on brewing times and methods. The average daily US consumption ranges between 200-250 mg per day. Adults receive two-thirds of their daily caffeine from coffee. Children receive one-half of their caffeine from soft drinks. Individuals worldwide consume about 76 mg caffeine per day.