In 2026, there’s almost nothing we don’t know about our bodies. From how we sleep to how the food we eat interacts with our microbiome to exactly what our blood sugar gets up to throughout the day, rare is the metric that remains a mystery. And I recently decided to take things a step further: I completed the 10X Health System genetic test, to learn what secrets were lurking in my genes and how I could positively harness the information for the benefit of my health.
Besides having a slightly dubious detoxification system, the main takeaway from my results was my body’s genetic inability to process caffeine. I’d long suspected I had a systemic intolerance to coffee, matcha and caffeinated tea, largely because of how off-kilter it makes me feel.
You may not want to know whether or not your body is particularly adept at processing caffeine and I respect that – so long as you’re not pounding a dozen espressos a day, you should be fine (current guidelines suggest adults should not exceed 400mg of caffeine a day, which is the equivalent of four to five cups of coffee or matcha). If you are interested, though, read on.
How your genes determine your caffeine intolerance
Prepare yourself for some unpronounceable genetic terms. “The CYP1A2 enzyme gene in the liver is responsible for breaking down roughly 95 percent of all caffeine consumed,” Dr Pascale Ricci, head of precision nutrition at Reviv Global, a brand that works alongside 10X Health, tells me. “The rs762551 SNP (single-nucleotide polymorphism) determines how fast or slow it occurs.”
Right, let’s break that down: rs762551 is a variation of the CYP1A2 enzyme gene. It’s what determines how quickly or slowly your body can break down caffeine. Committing either term to memory is not important, but understanding the role they play in your caffeine tolerance is. A genetic test, like the one I did, produces one of three results: you’re either an AA, AC or CC.
AA: the fast metaboliser
Approximately 41 percent of people are AA or fast metabolisers of caffeine, meaning their CYP1A2 enzyme works efficiently. “Caffeine is cleared relatively quickly, with a typical half-life of around two and a half to four and a half hours,” Ricci explains. If you know someone who can have a fresh cup of coffee at 6pm and still sleep soundly, chances are they’re an AA.
AC: the intermediate metaboliser
Join me in the middling club, along with around 43 percent of the population! An AC gene variant suggests that one of your parents gave you a functioning gene and one gave you a defective one. This makes us okay at metabolising caffeine: not brilliant, not terrible.
CC: the slow metaboliser
Finally, 16 percent of the population are estimated to be slow caffeine metabolisers, with two copies of the slower gene variant. “This means caffeine lingers in the bloodstream for significantly longer and leads to higher plasma caffeine levels after a cup of coffee,” when compared to someone with an AA variant, Dr Ricci explains.
“In simple terms, if two people drink the same latte, the slow metaboliser (CC) will have caffeine circulating in their body for much longer than the fast metaboliser (AA), meaning the effects (both the good and the bad) last longer and feel stronger.”
How to tell which type of caffeine metaboliser you are
Short of a genetic test, Dr Ricci has a few pointers of things to look out for when thinking about how well you metabolise caffeine.
Sleep disturbances
Difficulty falling asleep and poor sleep quality, even when keeping caffeine consumption to the morning, can indicate slow caffeine metabolisation.
