咖啡可以让人保持清醒，达到一个兴奋状态，这都要归结于它内含的咖啡因。那么咖啡因是如何作用我们的神经，让我们保持兴奋的呢？

    Caffeine interrupts our daily sleeping patterns by altering the chemical reactions in our brain.

    An addictive drug that 90% of Americans consume every day, caffeine prevents us from getting our by increasing nerve activity in our bodies-keeping us alert and hyperactive.

    After drinking a hot cup of caffeinated coffee, the caffeine causes three different chemical reactions that boost our energy levels:

    It energizes us by pumping the hormone adrenaline into our systems.

    It increases dopamine levels within our bodies. Dopamine is a neurotransmitter that stimulates our "pleasure areas" in our brain making us feel good.

    It blocks the connection ofadenosine to nerve cells. Adenosine is the chemical that attaches to receptors in the brain and causes drowsiness by slowing down nerve cells activity.

    The addictive and mood altering effects caused by caffeine consumption has had an increasing impact on the soft drink industry. Over the past 25 years, the amount of soda consumed by Americans has doubled. For instance, Americans spent $54 billion on 15 billion gallons of soda in 1998.
Fifteen billion gallons of soda is the equivalent to every American chugging down 58512-once cans per year!

    Today, 70% of all sodas in the United States contain caffeine. Teenagers especially have become dependent on caffeinated sodas or what many refer to as "liquid candy." Teenage boys and girls drink about twice as much "liquid candy" as milk, whereas twenty years ago they drank twice as much milk as soda.

    While many soda companies argue that caffeine is necessary to a soft drink's flavor, many researchers have shown that most people are hooked to a soda's caffeine content-NOT its taste. Most people can't tell the difference between caffeinated and uncaffeinated soft drinks. Soda guzzlers prefer the soft drink brands that contain caffeine because the caffeine stimulates alertness and boosts of energy.

    adrenaline: 肾上腺素

    dopamine: 多巴胺

    neurotransmitter: 神经传递素

    adenosine: 腺苷