Many people enjoy a few cups of coffee each day, often without giving much thought to how it might affect their health. But a recent study from the University of Toronto and other research teams suggests that the impact of coffee on your kidneys may depend on more than just how much you drink — your genes could play a big role too.
The researchers focused on a gene called CYP1A2, which controls how quickly your body breaks down caffeine. Some people have a version of this gene that makes them slow metabolizers of caffeine, meaning caffeine stays in their system longer. Others are fast metabolizers, so their bodies clear caffeine more quickly.
To make this clearer, imagine two friends: Alice and Bob. They both drink about four cups of coffee a day. Bob’s body processes caffeine quickly — he’s a fast metabolizer — so the caffeine doesn’t stay in his system for long. Alice, on the other hand, is a slow metabolizer. The caffeine lingers in her body for much longer. That difference in how their bodies handle caffeine may have big consequences.
The study found that people like Alice, who are slow caffeine metabolizers and also heavy coffee drinkers (over three cups a day), were almost three times more likely to show signs of kidney problems than people like Bob, who clear caffeine faster.
The researchers looked at several warning signs of kidney issues, including:
- Albuminuria (a protein in the urine that signals kidney damage)
- Hyperfiltration (when kidneys filter too much blood, which can stress them out)
- High blood pressure, a known risk factor for kidney disease
The results suggest that caffeine builds up in the bodies of slow metabolizers and may harm the kidneys over time — especially if they drink a lot of coffee.
This adds a new layer to the long-running debate over whether coffee is good or bad for your kidneys. Some older studies suggested coffee might protect against kidney disease, while others raised concerns about its possible harmful effects. What this new study shows is that both may be true, depending on your genetic makeup.
It turns out that about half of all people carry the slow-metabolizer version of the CYP1A2 gene. This means millions of coffee drinkers could be unknowingly increasing their risk of kidney problems just by following what feels like a normal routine.
Fortunately, testing for the CYP1A2 gene is now widely available through clinics and even some at-home DNA testing kits. Knowing your caffeine metabolism type could help you make smarter choices about how much coffee — or other caffeinated drinks — you consume.
This research, led by Ahmed El-Sohemy and published in JAMA Network Open, also highlights the growing importance of personalized nutrition — the idea that what’s healthy for one person might not be healthy for another. As more is learned about how genes affect our response to food and drink, we may start to see more tailored advice from health professionals.
So, if you’re a heavy coffee drinker, it might be worth asking: How well does my body handle caffeine? A simple genetic test could help answer that question — and potentially protect your kidneys in the long run.
This study is a reminder that nutrition isn’t one-size-fits-all. As science moves forward, personalized health recommendations may become the new normal — helping each of us make better choices based on our unique bodies.
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