By Dr. Neil Weiner
South Florida Nephrology, Hollywood, FL.

Patients with chronic kidney disease are often taking several medications and have associated medical issues that require close attention. Some of the more common of these are:

  • High blood pressure
  • Diabetes
  • High cholesterol
  • Obesity
  • Heart disease

While medications are a cornerstone of effective short and long-term therapy, dietary modification of vitamins and minerals is a crucial component to one’s overall well being. One such mineral that may affect the health of people with kidney disease is Phosphorous.

Phosphorus is a mineral that makes up 1% of a person’s total body weight. It is present in every cell of the body. Most of the phosphorus in the body is found in the bones and teeth.

While the main function of phosphorus is in the formation of bones and teeth, it also plays an important role in how the body uses carbohydrates and fats. It is also needed for the body to do the following important things:

  • Utilize protein for cell and tissue growth
  • Maintenance of cell and tissue health
  • Repair of cells and tissues
  • Makes ATP, a molecule the body uses to store energy

Where is phosphorous in the diet? The main food sources are the protein food groups of meat and milk. A meal plan that provides adequate amounts of calcium and protein also provides an adequate amount of phosphorus. Although whole-grain breads and cereals contain more phosphorus than cereals and breads made from refined flour, this is a storage form of phosphorus called phytin, which is not absorbed by humans. Fruits and vegetables contain only small amounts of phosphorus. Here is a partial listing of some common foods that have high amounts of phosphorous:

  • Ale, Beer
  • Dark Colas/Sodas
  • Milk based drinks
  • Canned iced teas
  • Cheese
  • Custard
  • Milk
  • Ice Cream
  • Meats
  • Liver
  • Oysters
  • Baked Beans
  • Chick Peas

So what’s the big deal? While at first glance this may not seem important but it is important to note that a high phosphorus level in the blood is one of the most powerful risk factors for cardiovascular disease in patients with kidney disease.  Elevated phosphorus levels in the bloodstream directly promote calcification in the coronary arteries, heart valves, and arteries elsewhere in the body.  Heart disease is the leading cause of death amongst patients with kidney disease (regardless of whether someone requires dialysis or not).

As kidney disease progresses, and especially at later stages of kidney disease (usually once the kidneys function below 40%, as a rough estimate), the kidney is unable to handle dietary phosphorous leading to retention of phosphorus in the blood stream.  Think of a stopped bathtub drain! Medications (such as phosphate binders) are often required to lower the amount of phosphorous absorbed in the gut and prevent it from accumulating in the blood stream.  But even with this-  clearly dietary restriction of phosphorus is vital.  You are what you eat!

The goal is to keep your phosphorus level normal.   A phosphorus level should be checked with your routine kidney-related lab work, especially if your kidneys are functioning at less than 40%.  A normal phosphorus level is 2.5 to 4.5 mg/dL. The National Kidney Foundation recommends that kidney patients ask your doctor or dietitian what your last phosphorus level was and write it
down. Be aware!

Speak with your nephrologist as to whether or not a diet low in phosphorus would be beneficial for you.

References:

  1. Alison Evert, MS, RD, CDE, Nutritionist, University of Washington Medical Center Diabetes Care Center, Seattle, Washington. Online: nlm.nih.gov/medlineplus/ency/article/002424.htm
  2. National Kidney Foundation: kidney.org