Overconsumption of Watermelon Reveals Deadly Risk of Kidney Damage

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Overconsumption of Watermelon Reveals Deadly Risk of Kidney Damage

Overconsumption of Watermelon Reveals Deadly Risk of Kidney Damage

There’s nothing quite as refreshing as biting into a slice of watermelon on a hot day. With the approaching watermelon season in the United States, many people are looking forward to enjoying this naturally sweet fruit. Because watermelon is 92% water, it shouldn’t pose any health problems, right? Not quite. 14% of American adults have chronic kidney disease (CKD)—a group that should be very cautious when eating watermelon, as a series of new case studies explore how people’s favorite fruit can lead to life-threatening issues.

Three case studies recently published in the Annals of Internal Medicine highlight a problem that has not been fully recognized: watermelon contains a remarkably high amount of potassium. While this usually isn’t a problem, it can be for people with CKD, a condition estimated to affect 35.5 million American adults, or about 14% of the population.

CKD refers to all diseases that affect the kidney’s ability to filter blood and remove waste. Nine out of ten CKD patients are unaware they have the condition, as it is often diagnosed when symptoms are more pronounced in the later stages.

Overconsumption of Watermelon Reveals Deadly Risk of Kidney Damage

Why is potassium important, and why is high potassium harmful?

Potassium is essential for the normal functioning of all cells. It regulates heartbeat, ensures muscles contract and nerves function properly, and balances fluid levels inside cells.

In adults, the normal range for blood potassium levels is between 3.6 and 5.2 millimoles per liter (mmol/L). Low potassium in the blood is called hypokalemia, and high potassium is called hyperkalemia, which is the focus here.

Mild hyperkalemia usually has no symptoms, but levels around 6.5 to 7 mmol/L can cause arrhythmias (including cardiac arrest, where the electrical system of the heart fails or “flatlines”), muscle weakness, or paralysis.

However, patients with long-term or chronic hyperkalemia, such as those with CKD, may not show symptoms at higher levels. For them, consuming more potassium from food can elevate potassium to dangerous levels.

In the cases published in the Annals, three patients with various forms of CKD developed hyperkalemia after consuming large amounts of watermelon over periods ranging from three weeks to two months.

Patient 1

A 56-year-old man with insulin-dependent type 2 diabetes and severe (stage 4) CKD was admitted to the intensive care unit (ICU) after a 15-second loss of consciousness or fainting episode. He had a very low heart rate of 20 beats per minute (bpm; normal resting heart rate is 60 to 100 bpm) and very low blood pressure: 62/32 mmHg. Laboratory tests showed his blood potassium level was 7 mmol/L; before admission, his blood potassium level was around 4.5 to 5 mmol/L. Hyperkalemia was successfully treated.

The man reported eating “large amounts” of watermelon every night for the past two months. The doctors diagnosed him with hyperkalemia, attributed to increased dietary potassium intake, combined with his severe CKD, the use of an antihypertensive medication (lisinopril), and possibly long-standing diabetes causing the kidneys to not excrete enough potassium. After advising him to reduce his watermelon intake, hyperkalemia did not recur.

Patient 2

In the second case, a 72-year-old male patient with ischemic cardiomyopathy (damage to the heart muscle due to inadequate blood supply, leading to impaired pumping function) and an automatic implantable cardioverter-defibrillator (AICD) was admitted to the ICU after his defibrillator shocked him.

On examination, his blood pressure was 176/90 mmHg, his heart rate was normal at 66 bpm, and his electrocardiogram was normal. Laboratory tests showed a blood potassium level of 6.6 mmol/L. The patient was taking the antihypertensive drug valsartan.

Information from the AICD indicated that a ventricular tachycardia (VT) and ventricular fibrillation (VF or V-fib) had triggered the shock. VT is when the lower chambers of the heart beat too fast. VF is when the lower chambers of the heart quiver rapidly and ineffectively; it is a life-threatening arrhythmia because it hinders the heart’s ability to pump blood effectively.

During the medical history, the man revealed that he had been drinking two glasses of watermelon juice daily for the month before the episode. The doctors concluded that valsartan combined with a high-potassium diet reduced the kidneys’ ability to unload potassium, leading to hyperkalemia and subsequent arrhythmias. The importance of avoiding high-potassium foods was explained to him, and three months later, his blood potassium level was within the normal range.

Patient 3

A 36-year-old female patient with end-stage kidney disease undergoing hemodialysis was found to have persistent asymptomatic hyperkalemia during monthly laboratory tests in the outpatient dialysis unit. Despite dialysis, her blood potassium level remained elevated at 7.4 mmol/L (previously below 5 mmol/L).

The woman admitted to eating “large amounts” of watermelon every day for the past three weeks, which was thought to be the cause of her hyperkalemia. The problem did not recur after she stopped overeating.

What do these cases illustrate?

Potassium is present in fruits such as dried apricots, prunes, raisins, orange juice, and the most famous potassium-rich fruit—bananas. Vegetables like potatoes, spinach, tomatoes, and broccoli, as well as dairy products, meats, poultry, and fish, and legumes, lentils, soybeans, and nuts also contain potassium.

As there is evidence that potassium intake is associated with lower adult blood pressure, heart disease, and stroke, the World Health Organization (WHO) recommended in 2023 that adults increase their potassium intake from food to at least 90 millimoles per day (3,510 mg/day).

A medium-sized baked potato with skin provides 925 mg of potassium, half an avocado provides 490 mg, an 80-gram (2.8-ounce) serving of salmon provides 534 mg, and the same amount of turkey provides 250 mg. Two tablespoons of peanut butter provide 210 mg, and a medium-sized banana provides 425 mg of potassium.

However, as demonstrated by this series of cases, a high potassium load can be life-threatening for people with impaired kidney function. While it is well known that bananas are rich in potassium, it is less commonly known that watermelon is also rich in potassium. One slice of watermelon contains 320 mg of the mineral, while a slice of 15 to 17.5-inch watermelon contains as much as 5,060 mg, nearly 1.5 times the recommended daily intake.

This study was published in the Annals of Internal Medicine.