- Drinking too much coffee may increase your risk of kidney problems, according to one study.
- Researchers say that half of people have a gene variant that nearly triples their risk of kidney issues from caffeine consumption.
- Experts explain if you should make any changes to your coffee habits.
Depending on how you take it, coffee offers many potential health benefits, from fighting inflammation to reducing risk of stroke and heart attack. But according to one study, drinking three or more cups of coffee daily increases kidney dysfunction risk—if you fall into a specific group of the population. Here, discover what the researchers found and whether you should adjust your coffee-drinking habits.
Meet the expert: Melissa Mroz-Planells, D.C.N., R.D.N., a national media spokesperson for the Academy of Nutrition and Dietetics and member of the Prevention Medical Review Board.
The study, which was published in JAMA Network Open, found that the presence of a particular gene variant can result in coffee being three times more likely to cause kidney dysfunction. This particular gene variant (rs762551 variant of the CYP1A2 gene) causes people to metabolize caffeine more slowly. The research authors noted that about half of the general population have this gene variant and are identified as “slow caffeine metabolizers.”
The study looked at 604 participants aged 18 to 45, regularly assessed over a 7.5-year follow-up period for 16 years. About half of the participants had the CYP1A2 gene variant. All participants had untreated stage 1 hypertension and had been recruited as part of a separate study.
Coffee intake was assessed through self-survey: a total of 158 participants (26.2%) consumed less than 1 cup of coffee per day, 379 (62.7%) consumed 1 to 3 cups per day, and 67 (11.1%) consumed more than 3 cups per day. The study assessed kidney health by tracking three signs of kidney dysfunction: albuminuria (excess protein in your urine), hyperfiltration (an abnormal increase in the filtration rate in your kidneys, which can lead to blood and excess protein in urine), and hypertension (high blood pressure).
People who metabolized caffeine more slowly and who drank three or more cups of coffee each day were 2.7 times more likely to have excessive protein in their urine, 2.5 times more likely to develop an abnormal increase in kidney filtration rate, and 2.8 times more likely to develop hypertension. For the fast metabolizers, their risk of developing these kidney problems was not associated with coffee intake. These findings strongly suggest that caffeine plays a role in the development of kidney disease in individuals who have stage 1 hypertension and possess the slow-metabolizing caffeine gene variant, specifically.
The relationship between coffee and kidney function
For most people, drinking coffee should not negatively affect kidney function, said Melissa Mroz-Planells, D.C.N., R.D.N., a national media spokesperson for the Academy of Nutrition and Dietetics and member of the Prevention Medical Review Board. In fact, a 2025 study published in Scientific Reports actually suggests that higher coffee consumption is associated with a lower risk of developing chronic kidney disease.
“The biggest concern about drinking coffee for people with kidney disease is that it is high in potassium,” said Mroz-Planells. “People with kidney disease following a lower-potassium diet will need to be mindful of how much coffee they consume in a day.”
There’s also the caffeine to consider. Caffeine is a stimulant, so it can increase your metabolic rate and stimulate your nervous system to break down fat, explained Mroz-Planells. “A concern with caffeine for those with kidney disease and high blood pressure is that too much caffeine can increase your blood pressure,” she added.
So, how much coffee is too much? Mroz-Planells said that, regardless of your risk of kidney problems, more than 600 milligrams (mg) per day of caffeine (or about six cups of coffee) is too much for most people. No more than 400 mg of caffeine or four cups of coffee per day is recommended for the average adult. But, this varies based on some other factors. “If you are someone with high blood pressure or are pregnant, you should consume no more than two cups of coffee a day since caffeine can increase blood pressure,” warned Mroz-Planells.
How can you tell if you’re a slow caffeine metabolizer?
While you can test blood or saliva for the CYP1A2 gene (which lets you know if you are a fast or slow metabolizer of caffeine), you can make an educated guess by how you feel after drinking coffee, said Mroz-Planells. “People who are fast metabolizers of caffeine will feel a peak about an hour after consuming caffeine. Slow metabolizers may not feel a peak until about four hours after they consume caffeine,” she explained. Mroz-Planells added that people who are slow metabolizers are more likely to experience side effects from caffeine such as feelings of restlessness, nervousness, or irritability, upset stomach, a fast heartbeat, difficulty sleeping, or more frequent urination.
However, that doesn’t mean that you can’t enjoy your morning cup of joe even if you do possess the slow-metabolizing gene. “People who are slow metabolizers can still enjoy caffeine in small amounts and earlier in the day,” said Mroz-Planells.
The bottom line
It’s important to keep in mind that in this study, the participants were identified as having untreated stage 1 hypertension. “High blood pressure is one of the common conditions associated with developing chronic kidney disease, so we can’t be sure if these results were due to caffeine intake, untreated high blood pressure, both, or something else,” explained Mroz-Planells.
So, take these findings with a grain of salt and know that caffeine is safe to consume, just not in excess. Too much caffeine for anyone, especially in those who are slow metabolizers, is not a good idea, Mroz-Planells said.
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