Coffee is part of the daily routine for millions of people, and its caffeine can make us feel more awake and alert.
But the same cup of coffee may not affect everyone in the same way. Research suggests that our genes could influence how quickly the body removes caffeine and whether heavy coffee drinking is linked to kidney problems.
Researchers led by Ahmed El-Sohemy at the University of Toronto examined a gene called CYP1A2. This gene helps control an enzyme in the liver that breaks down caffeine. Different versions of the gene can make this process faster in some people and slower in others.
People who break down caffeine quickly are often described as fast metabolizers, while those who process it more slowly are called slow metabolizers. For slow metabolizers, caffeine remains in the body for longer after drinking coffee. Researchers wanted to know whether this difference could affect kidney health.
The team analyzed data from 1,180 adults with untreated stage 1 hypertension who took part in a long-running study in Italy. Participants were followed for an average of about 7.5 years. The researchers examined their coffee habits, genetic differences, blood pressure, and several signs of kidney health.
The results suggested that drinking larger amounts of coffee was linked to a higher risk of kidney problems mainly among people who metabolized caffeine slowly. In this group, drinking three or more cups a day was associated with a greater chance of developing signs of kidney dysfunction.
These signs included albuminuria, which happens when a protein called albumin leaks into the urine. Healthy kidneys normally keep most protein in the bloodstream, so higher levels in urine can be an early sign that the kidneys’ filtering system is under stress or becoming damaged.
Heavy coffee consumption among slow caffeine metabolizers was also associated with a greater likelihood of unusually high filtration by the kidneys and with hypertension. Together, these findings suggest that prolonged exposure to caffeine may affect the kidneys differently depending on a person’s genetic makeup.
Importantly, the same pattern was not seen among people who processed caffeine quickly. This could help explain why past research on coffee has sometimes produced mixed results. Coffee may appear beneficial or harmful in different studies partly because people vary in how their bodies handle caffeine.
The findings do not mean that everyone should stop drinking coffee or that three cups will damage the kidneys. The study was observational, which means it can identify associations but cannot prove that coffee directly caused the kidney problems. The participants also had mild high blood pressure, so the results may not apply equally to every person.
Coffee itself is also a complicated drink containing hundreds of substances besides caffeine, including plant compounds with antioxidant effects. Previous research has linked moderate coffee consumption with several possible health benefits. The new findings suggest that genetics may be one factor worth considering when scientists study those effects.
Kidney health depends on many things, including blood pressure, diabetes, diet, physical activity, smoking, medications, and family history. People with kidney disease or high blood pressure who are concerned about caffeine should discuss their coffee intake with a health professional rather than making major changes based on genetic information alone.
The study was published in JAMA Network Open. It adds to the growing field of personalized nutrition, which investigates whether genetic differences can help explain why the same food or drink may have different health effects from one person to another.
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