If you learned that your genes make you a slow caffeine metabolizer, would you drink less coffee? It sounds obvious. A team at the Poznań University of Life Sciences (Bulczak and Chmurzynska, Nutrients, October 2025) tested it in a randomized trial with a three-year follow-up, and the answer is more interesting than a simple yes.
The caffeine gene in brief
Most of the caffeine you drink is broken down in the liver by an enzyme called CYP1A2. A common variant, rs762551, changes how quickly that enzyme works: people with two A copies tend to clear caffeine faster, while carriers of the C version clear it more slowly. In a well-known 2006 study in JAMA (Cornelis et al.), slow metabolizers who drank two to three cups a day had a higher risk of a non-fatal heart attack, and the risk rose further from four cups, while fast metabolizers showed no such increase.
The trial
The researchers recruited 94 adults aged 18 to 60, all carriers of the slow C version and all drinking at least 200 mg of caffeine a day, about two cups of coffee. Everyone received personalized nutrition advice on cutting down. The intervention group was also told their genotype: that they were slow metabolizers and that, in heavy coffee drinkers, this profile has been linked to a higher risk of heart attack. The program lasted 20 weeks, and intake was measured with a food questionnaire and a smartphone app. Participants were contacted again three years later.
The result: the gene added nothing measurable
- With genotype: from 381 to 154 mg of caffeine a day.
- Without genotype: from 394 to 170 mg a day.
- Difference between the groups: not significant, at 20 weeks or at three years.
Both groups cut their caffeine by more than half. Knowing the gene did not make people cut more. About half of the participants could be reached at three years, so the long-term figures are less precise.
Why?
The authors' explanation is simple: being told clearly that you should reduce caffeine, with a plan to do it, was enough of a trigger. The genotype acted as a supplement rather than the deciding factor. This fits a 2016 review in the BMJ (Hollands et al.), which found that communicating genetic risk has little or no effect on behavior on its own. Knowing is not doing: habits change through practical steps.
What to do with your CYP1A2 result
- Treat it as a reason to have a plan, not as a verdict. Your genotype tells you which side of the curve you are likely on; the plan is what changes your intake.
- If you are a slow metabolizer, keep intake moderate. In the Cornelis study the higher risk appeared from two to three cups a day.
- Move your last caffeine earlier. Slow clearance means caffeine stays in your system longer, which matters for sleep.
- Count every source: tea, cola, energy drinks, pre-workout powders and some painkillers contain caffeine too.
- Clearance is not sensitivity. How jittery or sleepless caffeine makes you also depends on other genes such as ADORA2A.
How we use it in our reports
That is exactly why our reports never stop at the genotype: each CYP1A2 result comes with concrete targets, timing and the sources to watch, and the Sport report adds how caffeine fits around training. See the reports.
Important: this article is educational and is not medical advice. If you have a heart condition, high blood pressure, are pregnant or take medication, ask your doctor what caffeine intake is right for you.