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11 things you should know about caffeine

  • What caffeine does to the body

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    Once you ingest caffeine, it enters the bloodstream through the stomach and small intestine and can begin to take effect within 15 minutes.

    Caffeine blocks the action of the brain chemical adenosine, which is associated with sleep, according to Harvard Medical School. However, because caffeine looks like adenosine to a nerve cell, it binds to adenosine receptors. When this happens, the cells speed up, causing blood vessels to constrict. Caffeine also triggers the release of adrenaline, the "fight or flight" hormone. The release of adrenaline causes muscle tightening and an increased heart rate and blood pressure.

    The physical effects of caffeine largely wear off within hours.

    Occasional low doses of caffeine have been found to produce "positive mood effects such as increased well-being, happiness, energetic arousal, alertness, and sociability," Johns Hopkins researchers report. Regular users build up a tolerance and may not experience the same positive effects; they need that morning caffeine infusion just to help overcome sleepiness and lethargy.