Eleventh century Arabians were known to have coffee beverages. And while exploring the New World, Spanish conquistadors were treated to a chocolate drink by Aztec Emperor Montezuma in 1519. The longstanding popularity of beverages that naturally contain caffeine attests to its appealing qualities. In some soft drinks, caffeine is added in small amounts as a key ingredient in the subtle flavor profile that provides each product's unique taste. Because caffeine consumption is so widespread, it is one of the most well-studied ingredients in the food supply.
Caffeine is a mild stimulant.
People differ greatly in their innate sensitivity to caffeine. Whereas many individuals can drink several cups of coffee within an hour and notice no effects, others may feel some effect after one serving. Caffeine does not accumulate in the bloodstream or body and is normally excreted within several hours following consumption. In sensitive individuals, tests show that caffeine can quicken reaction time and prolong vigilance of various demanding tasks. Many people, such as shift workers and college students studying late at night, find caffeine-containing beverages can help them stay alert to finish their work.