Bradley Mark Denker, M.D., is an assistant professor of medicine at Harvard Medical School. He is also the director of nephrology at Harvard Vanguard Medical Associates and an associate physician of the Department of Medicine at Brigham and Women's Hospital.

Question:

I've been diagnosed with polycystic kidney disease. Can you give me some information on the recommended daily intake of phosphate and potassium for someone with my condition?

Answer:

Polycystic kidney disease is an inherited disorder that leads to the gradual enlargement of numerous cysts in the kidneys and other organs. The disease gradually leads to kidney failure as the cysts enlarge over time and replace the normal kidney structures. The time it takes to develop kidney failure varies widely, with most people developing kidney failure between the ages of 40 and 80 years old.

The degree of kidney failure is a very important consideration for specific dietary recommendations. The kidneys excrete phosphate and potassium in the urine to remove these substances from the body. If potassium accumulates in the blood, it can be dangerous and lead to irregular heart rhythms (arrhythmias) and death. Therefore, people with kidney failure should not increase their potassium intake, and should limit their intake to less than 2 grams per day. Elevated phosphorous levels can lead to bone and cardiac problems and should be restricted to 1 gram per day. Both potassium and phosphate levels in the blood should be regularly monitored.

However, people with polycystic kidney disease who have near-normal kidney function do not need to restrict their phosphate and potassium. Some studies in animals suggest that restricting potassium can lead to more rapid cyst growth and more rapid loss of kidney function.

Some kidney doctors treat their patients with sodium or potassium citrate, a medicine that neutralizes the acid (alkalinizes) in urine. It is not clear whether it is the neutralization or the potassium that may provide the benefit. People should never start this therapy without specific instructions from a kidney doctor (nephrologist). In addition, people with polycystic kidney disease should avoid caffeine because it increases cellular levels of substances that can stimulate cyst growth.