Caffeine keeps people alert—a prized quality in an always-on world. It also stimulates the brain's pleasure centers, and it is mildly addictive—two possible reasons to add it to foods and drinks.

The burgeoning caffeinated-foods industry has raised eyebrows at the U.S. Food and Drug Administration. Although the fda does not regulate caffeine—and says less than 400 milligrams a day “is not generally associated with dangerous, negative effects”—it is reconsidering regulation because manufacturers are putting caffeine in many products, at high doses (vertical axis) and large serving sizes (horizontal axis). (Coffees rank highest, yet energy drinks may pack a bigger punch because they contain a cocktail of other ingredients.) The fda is concerned about the cumulative intake of caffeine throughout the day, which could lead to dependency. Also, the American Academy of Pediatrics warns that consumption by children may be linked to neurological and cardiovascular problems.

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