If the first thing you reach for in the morning is a cup of coffee or soda and the quick surge of energy that jolts you awake, you might want to think twice. Most of us know that caffeine is addicting, but do you have any idea how much caffeine you actually take in each day?

• How caffeine acts in our body
• Negative effects of caffeine
• Caffeine in 10 foods
• How much is too much?

How caffeine acts in our body

Caffeine is a mild central nervous system stimulant. It "wakes up" the brain, stimulates the digestive tract, speeds up metabolism and raises brain levels of serotonin, a neurotransmitter that affects mood. Athletes sometimes use caffeine to help release additional free fatty acids for energy, sparing precious glycogen for later use. Caffeine is also found in many supplements advertised as "fat-burners" because of its effect on metabolism.

Negative effects of caffeine

In high doses, caffeine can cause:

• Rapid heartbeat
• Irritability
• Insomnia
• Anxiety and nervousness
• Dehydration from diuresis (that irksome need to pee in large quantities)
• Indigestion
• Lack of concentration
• Muscle twitching