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

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

It energizes us by pumping thehormoneadrenalineinto our systems.

It increasesdopaminelevels within our bodies. Dopamine is aneurotransmitterthat stimulates our "pleasure areas" in our brain making us feel good.

It blocks the connection ofadenosineto 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 billion on 15 billion gallons of soda in 1998.