Relationship to caffeine? It’s complicated.

For some people, caffeine is the perfect, lowkey spark to get them going in the morning. For others, it sends them over the edge with jitters and anxiety. And then there are folks that say caffeine does nothing for them — what’s up with that?

When we started looking into it, we realized that it’s pretty complicated! Your caffeine tolerance is affected by everything from what you had for breakfast to your genetics.

The science behind it goes way deeper, but basically, this is what happens when you drink coffee: Caffeine enters your bloodstream through your stomach and intestines, and as it circulates your body, it joins up with a number of “receptors,” most of which are in your brain. Each person’s adenosine receptors are different due to genetics, and caffeine might not bind well with them. Folks who say caffeine does nothing to them probably do not have very “sticky” receptors.

After joining up to your receptors, caffeine travels to your liver, where it’s metabolized. That’s the second point where genetics come into play. In your liver, there’s a cocktail of enzymes that are designed to tackle different substances. The CYP1A2 enzymes are the ones that metabolize caffeine, and some people produce less of the one that knocks out caffeine quickly (the CYP1A2*1F (rs762551) enzyme, to be exact). If a coffee at 11am still has you wired at 4pm, you’re probably a slow caffeine metabolizer.

Okay, so genetics are the main reason caffeine affects people differently, but what else?

Well, one big factor is how much coffee you drink on the daily. Even if someone is a fast-metabolizer of caffeine, they may still feel the effects more strongly if they don’t drink it regularly. Those who have been drinking coffee for a long time develop a tolerance and caffeine doesn’t quite have the edge it used to.

And then there’s everything else you’re eating and drinking. Food, beverages, medicine, drugs, anything you ingest affects the way other things are metabolized. Some enzymes metabolize multiple substances, so each one has to “wait its turn,” which slows down the process and keeps the substance in your system longer. Oppositely, smoking cigs speeds up the rate at which caffeine is metabolized, which explains why smokers stereotypically drink a lot of coffee — it’s leaving their system faster.

So, what about you? Is it a love/hate relationship with caffeine, or something else entirely?

Written by Philly Coffee Writer, Kate Kelly.

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