You might have heard "kidneys" and "potassium" mentioned in the same breath and assumed that potassium was good for the kidneys. Nothing could be further from the truth, because while kidneys and potassium are related, the association is not a positive one. Too much potassium is downright hazardous for kidney patients. Low-potassium diets are often recommended to minimize the symptoms of renal failure.
Potassium
Short of extreme starvation or anorexia, potassium deficiencies due to lack of dietary potassium are almost unknown because this mineral is so common that it's even found in tap water. Normal levels are between 3.5 and 5.0 mEq/l. Regardless of how much potassium you consume, healthy kidneys keep potassium levels in this range and excrete any excess.
Regulation
Potassium levels are tightly regulated and kept within a narrow range because if levels get too high or too low, nerves will not fire appropriately. A network of hormones and enzymes called the renin angiotensin aldosterone system, or RAAS works together to keep potassium levels in a safe range. Since potassium is so important, multiple systems protect potassium levels.
High Potassium Levels
As chronic kidney disease becomes more advanced, the kidneys are less able to remove excess potassium from your body. Serum potassium levels start to increase, which causes nerves to function unreliably. Since the heart beats in response to input from nerves, high potassium levels can cause tachycardia, arrythmias and even heart attacks. For people with these issues, potassium is decidedly not good for kidney function.
Low Potassium Levels
The National Kidney Foundation reports that keeping potassium levels within a normal range is particularly difficult for dialysis patients, given the intermittent nature of dialysis treatment. If you have advanced kidney disease or you are on dialysis, your nephrologist will tell you if a low potassium diet is necessary. The NKF defines a high potassium food as one that has more than 200 mg of potassium per serving. These foods include potatoes, sweet potatoes, lentils, dried beans, broccoli, tomatoes and bananas. Avoiding these foods helps keep potassium levels in check.
