Wikipedia:Reference desk/Archives/Science/2019 October 10

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October 10

When is the very last molecule of coffee cleared from the body?

Popular sources on sleep say that caffeine has a half-life of 6 hours. So my cousin read this and cheekily pointed out that this would imply traces of caffeine will still be in our bodies millions of years from now. I have tried to find some serious answer to this, but most people just talk about when the effect of coffee wears off. So, according to this paper, "caffeine's elimination half-life may range between 1.5 and 9.5 hours, while the total plasma clearance rate for caffeine is estimated to be 0.078 L/h/kg". Based on this, if I drink one cup of coffee now, when would the very last molecule of caffeine be cleared from my body? Vesal (talk) 11:58, 10 October 2019 (UTC)

Apparently you're talking specifically about Caffeine rather than coffee, which has a significant amount of water in it. What's unclear to me is whether a caffeine molecule remains intact or whether it is broken down by digestion. I don't see that in the article. ←Baseball Bugs ^{What's up, Doc?} carrots→ 12:30, 10 October 2019 (UTC)

Almost 100% of the caffeine makes it into your circulation in tact. This is seen in the bioavailability listed in our article. Someguy1221 (talk) 12:39, 10 October 2019 (UTC)

Yes, but a small portion of the caffeine doesn't make it inside tactfully, but rather rudely, in the form of a coffee enema. SinisterLefty (talk) 02:03, 12 October 2019 (UTC)

(edit conflict) If we make the probably naive assumption that caffeine's elimination follows a simple exponential decay, and assume that our subject has consumed a single cup of coffee containing 95mg of the good stuff, then from the molar mass of the molecule and avogadro's number, we can conclude that after 68 half lives, there is only a single molecule expected to remain. Again, assuming simple exponential decay, this one molecule has a 50% chance of still being around after one half life, ad infinitum, but once it's gone it's gone. Someguy1221 (talk) 12:33, 10 October 2019 (UTC)

Wow. 68 half lives of c.6 hours is a seriously long time. So why is it that caffeine addicts feel the need for more in massively less than one half life? --Dweller (talk) Become old fashioned! 12:49, 10 October 2019 (UTC)

Typically one cup of coffee gives you a plasma concentration of caffeine of about 4uM. From rodent studies, by 1uM you're already down to undetectable effects on brain activity. It also matters which type of brain activity you're focused on. Caffeine has a half life of typically four hours in a rat, but some effects of caffeine are already gone in less than two after a dose of caffeine. See [1] for example. Someguy1221 (talk) 13:23, 10 October 2019 (UTC)

{{ec}} Is there some threshhold of effect? (ec: I see Someguy1221 addresses this). If one thrives on having the effect of the caffeine-level gotten after a single cup, after ca. 6 hours, you're already down by half and need a booster shot. And even after 1 hour, you're already down from where you started. I'm not sure which of our steady state articles is relevant to pharmacology and drug-dosing. And this is all assuming there is no lag after ingestion. If the caffeine level were to gradually rise or have a delayed effect, the 10 minutes after the first cup "I don't feel more awake, better drink another". Which reminds me, it's been 10 minutes since my last cuppa... DMacks (talk) 13:25, 10 October 2019 (UTC)

I'm assuming in addition to the matter of threshold, there is likely also a degree of short term desensitization. Someguy1221 (talk) 13:36, 10 October 2019 (UTC)

Caffeine#Dependence and withdrawal mentions tolerance and the subarticle caffeine dependence discusses the physiological basis of it in more detail. DMacks (talk) 13:46, 10 October 2019 (UTC)

Atoms and molecules are incredibly tiny. For a fun illustration, to a zeroth-order approximation a human head contains 456000000000000000000000000 atoms (4.56×10²⁶). 100 mg of caffeine, very roughly an average dose, consists of around 310120000000000000000 molecules (3.1012×10²⁰). Way before you get down to a few molecules of caffeine, you're going to lose any effect. The molecules might not even be in your brain, which they need to be to have any psychoactive effect. Your body contains random amounts of lots of things, but mostly in too low an amount to have any real effect. --47.146.63.87 (talk) 23:07, 10 October 2019 (UTC)

This thread is why I still read Reference Desk. It quantifies the unquantifiable and unscrews the inscrutable.Edison (talk) 23:52, 11 October 2019 (UTC)

Also, it's about coffee! --Stephan Schulz (talk) 00:09, 12 October 2019 (UTC)