YOU may have heard adults say they can’t get going in the morning without a cup of coffee. One reason they may feel that way is that coffee contains caffeine (咖啡因), something known to give an energy boost (提升). Caffeine occurs naturally in coffee, tea and cocoa beans, which are used to make chocolate. But now food makers are adding the stimulant (兴奋剂) to many products, from popcorn and potato chips to waffles (华夫饼) and water. “It’s possible for all of this caffeine consumption to add up and become dangerous,” says Virginia Stallings, a doctor at the Children’s Hospital of Philadelphia.