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How Long Before Bedtime Should I Have My Last Coffee?

By Jeremy Chin
Posted on 25 Aug, 2015

How Long Before Bedtime Should I Have My Last Coffee
Each day, coffee saves many a student, defibrillates working adults and resurrects depleted parents. But coffees’ most valued attribute as a picker upper can morph into a nightmare, especially when it’s bedtime and you discover you’re too wound up to wind down.

But how long does coffee eddy in your system? It’s different for everyone. Some can go from chatty to comatose right after coffee. Some end up being the host of an all-night sheep-counting soiree. For the average healthy person, it takes 5.7 hours for caffeine to reach its half life. Which means, if you drank 200 mg at noon, you’d still have 100 mg in your blood at 6 pm.


Understanding CYP1A2

CYP1A2 may sound the offspring of C3P0 and R2D2, but it’s not. It’s actually the gene required by the liver to demethylate caffeine molecules. Simply explained, it transforms caffeine into other substances, chiefly paraxanthine, which is ultimately excreted in the urine. More simply explained, it turns caffeine into pee.

The speed with which caffeine is cleared from the body is proportional to the amount of available CYP1A2 in a person. And this changes based on genetic disposition, substances in your body at the time and your overall physical condition.


Things That Prolong Caffeine Half Life

Oral Contraceptives
Birth control pills cripple the body’s ability to break down caffeine. As such, the staying power of caffeine for women on the pill is approximately 12 to 15 hours.


Grapefruit Juice
Narigenin, the chemical that makes grapefruit juice bitter, inhibits the production of CYP1A2. This can prolong the life of caffeine in your body by more than 30%.


Maternal metabolism of caffeine is slowed during pregnancy. As a result, the half-life of caffeine is 10-20 hours for pregnant women. Caffeine can also cross the placenta from the maternal to fetal bloodstream. The caffeine half-life in newborns can be as long as 4 days.


Being Asian
Asians metabolize caffeine slower than Caucasians. However, more studies in non-Caucasian ethnicities are needed to complete our understanding of these genotype effects.


Liver Disease
Because caffeine is broken down in the liver, the half-life of caffeine for someone with liver disease can be as long as 96 hours.


Alcohol is a strong inhibitor of caffeine metabolism and increases caffeine half-life by 72%. There have been many who have spoken out against combining alcohol with caffeinated beverages. They say it disturbs the peace; chiefly because the result is usually “the wide-awake drunk”.


Coffee With Milk
Because your body metabolises milk slower, the caffeine in a milky cappuccino will work through your system slower than a cup of black filter coffee or an espresso.



Things That Speed Up Caffeine Disposal

Nicotine doubles the rate at which caffeine is depleted, which may offer insight into why many smokers are also heavy coffee drinkers. Because caffeine flushes from their system at twice the speed, they tend to double their dosage to obtain the same effect of a non-smoker.


It has been found that eating broccoli and other cruciferous vegetables induces the production of CYP1A2, allowing caffeine to be metabolized quicker.



Wonder why half life is used as a measurement?
Before caffeine can be flushed from the system, it needs to be broken down. This process doesn’t happen all at once, but at an exponential rate. Half life is perhaps the most common measurement for the decay of an entity.


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