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. Caffeine symptoms appear to be dose related. Most people experience no behavioral affects with less than 300 mg caffeine. Sleep is more sensitive and can be disrupted by 200 mg caffeine.