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Caffeine
Pronunciation
Definition 1
A substance found in the leaves and beans of the coffee tree, in tea, yerba mate, guarana berries, and in small amounts in cocoa. It can also be made in the laboratory, and is added to some soft drinks, foods, and medicines. Caffeine increases brain activity, alertness, attention, and energy. It may also increase blood pressure, heart rate, breathing rate, and the loss of water from the body in urine. (NCI Dictionary)
Definition 2
A naturally occurring xanthine derivative with central nervous system (CNS) stimulating activity. Due to the structural similarity to adenosine, caffeine binds to and blocks adenosine receptors, thereby preventing the inhibitory effects of adenosine on nerve cells. This leads to stimulation of medullary, vagal, vasomotor, and respiratory centers in the brain; and the release of epinephrine. Physiologic responses can include bradycardia, tachycardia, vasoconstriction, CNS excitablility, increased respiratory rate, increased blood pressure, increased blood flow to muscles, decreased blood flow to skin and inner organs, and release of glucose by the liver. Due to the interaction between adenosine A2A and dopamine D2 receptors, caffeine can also indirectly increase the levels of dopamine in the brain. (NCI Thesaurus)
Definition 3
An alkaloid stimulant having a purine double-ring structure composed of eight carbons and four nitrogen atoms with methyl groups attached to the nitrogen atoms at the 1, 3, and 7 positions and having double bonds at the carbons in positions 2 and 6. (NCI Thesaurus/CRCH)
More information
Caffeine is a bitter substance found in coffee, tea, soft drinks, chocolate, kola nuts, and certain medicines. It has many effects on the body's metabolism, including stimulating the central nervous system. This can make you more alert and give you a boost of energy.
For most people, the amount of caffeine in two to four cups of coffee a day is not harmful. However, too much caffeine can cause problems. It can
• Make you jittery and shaky
• Make it hard to fall asleep or stay asleep
• Cause headaches or dizziness
• Make your heart beat faster or cause abnormal heart rhythms
• Cause dehydration
• Make you dependent on it so you need to take more of it. If you stop using caffeine, you could get withdrawal symptoms.
Some people are more sensitive to the effects of caffeine than others. They should limit their use of caffeine. So should pregnant and nursing women. Certain drugs and supplements may interact with caffeine. If you have questions about whether caffeine is safe for you, talk with your health care provider. (Food and Drug Administration)
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