Patients with reduced kidney function, also known as renal insufficiency, often require complex diets. Otherwise healthy foods, such as dairy products, tofu and lentils, become off-limits because they can raise phosphorus levels, which in turn raise serum calcium levels. Reduced kidney function makes calcium regulation unpredictable. Patients should never take calcium supplements or deviate from the instructions of their nephrologists or renal dietitians. Any changes in calcium intake need evaluation in light of the patient's laboratory reports.
Calcium
The balance between calcium in your bones and calcium in your bloodstream is central to any analysis of calcium intake. Ninety-nine percent of the calcium in your body is in the bones, with the remainder in the blood. The concentration of calcium in blood is critical to many biological functions. Not only does it play a key role in the transmission of nerve impulses, but it is also involved in the dilation and construction of blood vessels. Higher than normal serum calcium levels undermine these important functions.
Calcium Regulation
Healthy people have no problem keeping serum levels of calcium constant because calcium is regulated by a complex interplay between phosphorus, parathyroid hormones and calcitriol, or vitamin D-3. If calcium levels get too low, parathyroid hormone converts vitamin D-2 into D-3, or calcitriol, which in turn stimulates the release of calcium from bone. Phosphorus also plays a role, as it too can pull calcium from the bones. If serum calcium levels are too high, healthy kidneys excrete whatever is unnecessary.
Reduced Kidney Function
People with reduced kidney function have a much harder time keeping calcium levels constant. In many instances, their kidneys cannot regulate phosphorus levels effectively. High serum phosphorus levels cause serum calcium levels to rise. Since these patients' kidneys cannot effectively convert vitamin D-2 to D-3, they are less able to correct for low levels of serum calcium. Doctors often intentionally ignore low levels of D-3 if phosphorus levels are high because higher levels of D-3 would only aggravate problems related to high calcium levels.
Calcium Intake
Patients with advanced disease who are on low-phosphorus diets often consume less dietary calcium because many high-phosphorus foods, such as dairy products, are also high in calcium. Patients don't need to compensate for getting less calcium by eating high-calcium foods because this would increase phosphorus levels and cause calcium to be driven from the bone. Nephrologists routinely monitor calcium levels and can advise if supplements are appropriate or if the patient should take calcium binders to get rid excess serum calcium. Patients should never take calcium supplements without consulting their nephrologists because this could further upset a very tenuous metabolic situation.
