All over the web people are talking about the Caffeine Zone 2 app, which supposedly lets you keep track of how much caffeine is in your system.  It considers factors such as how much caffeine you’re consuming, the caffeine source (e.g., coffee or tea), and how long it takes you to consume it.  The app generates a chart that supposedly indicates your predicted caffeine level for 24 hours.  The chart includes a green cognitive active zone, during which time caffeine is supposed make most people feel active, and a blue sleep zone, during which time most people will be able to sleep.

Caffeine Zone iphone app

Unfortunately, this caffeine app does not work!  The reason is that there are well over a dozen pharmacokinetic factors that affect the way that caffeine is metabolized and the speed at which it is metabolized.  This little app doesn’t even attempt to take into account most of these factors, and, therefore, is completely incapable of doing its job!
To see how complex the process of caffeine metabolism actually is, consider the following handful of factors that affect the speed and extent that caffeine is metabolized:  Women generally metabolize caffeine faster than men.  Smokers process it twice as quickly as  non-smokers do.  Women taking birth-control pills metabolize it at perhaps one-third the rate that women not on the pill do.  Asians may do so more slowly than people of other races.  Obese people metabolize caffeine more slowly than lean people.  And introverts are significantly less affected by caffeine than extroverts.  Genetic predispositions also dramatically alter the effects of identical doses of caffeine on different people.
If you consider even these few additional factors, you might not be surprised to learn a non-smoking, fat Japanese man drinking his coffee with an alcoholic beverage — another slowing agent — would be likely to feel caffeine about five times longer than a skinny Englishwoman who smoked cigarettes but did not drink or use oral contraceptives!  (For a more complete presentation of factors affecting caffeine metabolism see our page on “Drug and Food Interactions with Caffeine.“)
So, nice try, but no cigar for this silly and useless app.


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