Caffeine is found naturally in or added to many foods and beverages, from sodas and teas to coffee, chocolate and sports drinks. Many people consuming these products depend on the inherent “buzz” factor associated with caffeine, a known stimulant. Understanding the mechanics of how the drug enters the brain may help those with sensitivities understand their tolerance levels.
Ingestion
Caffeine’s effect and rate of absorption is dependent largely on the quantity the individual consumes and his particular sensitivity. For example, a person with mild tolerance may find caffeine’s noted side-effects, such as nervousness and hyper-alertness, too much to bear after drinking as little as one 8-oz. cup of regular coffee. Conversely, a regular coffee drinker may not experience the same effect until he's consumed more than a cup. This is due to brain receptors that absorb caffeine on a molecular level and the amount of the chemical adenosine in the brain at the time of consumption.
Reception
The human body regularly produces adenosine as a byproduct of any of the thousands of neurons that fire during the course of the day. Adenosine isn’t a waste product, however; according to the book “Nutrition: Concepts & Controversies,” certain receptors are in charge of making sure adenosine maintains a certain manageable level. When adenosine levels rise, the receptors trigger the brain’s sleep response. One such receptor named A1 is the receptor on which caffeine has the highest and most dramatic impact.
Caffeine
Once a person consumes a cup of coffee, caffeine quickly enters the bloodstream and makes headway toward the brain, where it’s intercepted by receptors such as A1. A1 interprets caffeine as adenosine and “accepts” it as real adenosine, allowing it enter into all the receptors. Once in, caffeine quickly "snuggles up" to all the receptors it encounters and plugs the receptor’s abilities. For tolerant persons, however, this may take higher levels of caffeine and a longer period of time. Other chemicals that act opposite of adenosine, such as dopamine, roam around unchecked, leading to increased feelings of alertness and excitability.
Aftereffect
The length of time caffeine stays in the brain and continues to act as an “imposter” is dependent on whether or not the consumer drinks more caffeine. Generally speaking, as the receptors discover they’ve been duped by caffeine’s imposter-like effects, the blood filters it away and the receptors return to normal, according to Washington State University. Caffeine is filtered out by the kidneys and flushed away as waste usually an hour after ingestion, then all receptors and adenosine levels return to normal.
References
- "Nutrition: Concepts & Controveries, 7th Ed."; Frances Sizer Webb & Ellie Whitney; 2006
- Washington State University: Caffeine Overview
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