|MadSci Network: Medicine|
Caffeine is a stimulant. It belongs to the class of chemical compounds referred to as methylxanthines. The naturally occurring methylxanthines found in plants act as pesticides against many kinds of insects. In you and me caffeine merely gives us a buzz; that extra little perk to get going in the morning. It does so by binding to adenosine receptors at certain sites in the body. The result of this stimulation leads to heightened mental awareness, increased heart rate and other effects.
As for being a source of energy -- it depends what you mean.
If you light powdered caffeine with a match it will combust, releasing energy in the form of heat. However, our bodies do not use combustion to generate energy. Instead we use the process of respiration whereby cells in our body derive energy from the electrons in certain chemical compounds, commonly sugars and fats. As far as I am aware no higher animal or plant has the necessary enzymatic machinery to use caffeine as a source of energy. There are many species of microbes that can eat 'strange' things, and I'm certain caffeine would be on the list. Our increase in 'energy' after eating or drinking things with caffeine in them comes about from the effects of caffeine on cellular receptors in the body, not from its direct use as a source of energy.
Thanks for your question!
-Lynn Bry, MadSci Admin
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