How late is too late in the day to drink caffeine?

There's definitely a lot of individual variation here,

but knowing the half-life of caffeine would be useful,

especially if you actually understood what the half-life of a substance actually means.

Hello, I'm Monica Rineagle, and this is The Nutrition Diva Podcast, a show where we take a closer look at nutrition news, research, and trends, and answer your food and nutrition questions.

And a listener recently wrote to me after reading that caffeine has a half-life of six hours and wondering what that actually means. This is such a good

question because while most of us are familiar with that term, half-life, few of us have a good

grasp on what it does actually mean. You usually hear it applied in the

context of medications, and not foods, or even nutrients. But even though it is a natural compound,

caffeine is actually a drug. And that means that the tools that we use to measure how drugs move through the

body apply here as well. So let's get into this. When scientists talk about the half-life of a substance,

they are describing how long it takes for the level of that substance in your bloodstream

to drop by half.

Now, that clock does not start the minute you swallow a pill, or in the case of caffeine,

take a sip of coffee, there is a short delay while your body absorbs it.

But once it is fully absorbed and circulating, then half-life refers to the speed at which your liver and kidneys will clear it from your system.

So if something has a two-hour half-life, that means that once that substance has peaked in your bloodstream, it will take about two hours for your body to reduce that concentration

by half. Now, at this point, you might be wondering why we don't just measure the total time it

takes to leave the body altogether. That does seem simpler, doesn't it? And the reason that we don't

do this is that the decline is not

linear. So if the half-life of a substance is two hours, it might sound like it should then take

four hours to eliminate it completely. But in fact, it'll take eight to ten hours before it's completely out of your system.

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