Program for kidney disease patients effective for reducing serum phosphorus levels

Patients with end-stage renal disease (ESRD) who participated in an education program to limit their intake of phosphorus-containing food additives lowered their blood levels of the chemical, according to a study in the February 11 issue of JAMA, the Journal of the American Medical Association.

Individuals with moderate to severe kidney disease have an impaired ability to excrete phosphorus, and as a result, they tend to develop hyperphosphatemia (abnormally high concentration of phosphates in the blood), especially if their intake of phosphorus is high. Elevated serum phosphorus levels are associated with an increased risk of death and illness, with levels greater than the 5.5-mg/dL level recommended by practice guidelines associated with a 20 percent to 40 percent increase in the risk of death among patients with ESRD. In addition, hyperphosphatemia appears to be involved in the development of a number of health risks, including heart disease and bone disease, according to background information in the article.

To prevent hyperphosphatemia, patients with ESRD limit their intake of foods that are naturally high in phosphorus such as meats, dairy products, whole grains and nuts. However, phosphorus-containing additives are increasingly being added to processed and fast foods, particularly meats, cheeses, baked goods and beverages. The effect of such additives on serum phosphorus levels is unclear.

Catherine Sullivan, M.S., R.D., L.D., of MetroHealth Medical Center and Case Western Reserve University, Cleveland, and colleagues tested an educational intervention to reduce the intake of additive-containing processed and fast foods to determine if there is a causal relationship between additive consumption and hyperphosphatemia among patients with ESRD. The study included 279 patients with elevated baseline serum phosphorus levels (greater than 5.5 mg/dL). About half of participants reported eating fast food more frequently than once a week. Intervention participants (n = 145) received education on avoiding foods with phosphorus additives when purchasing groceries or visiting fast food restaurants. Control participants (n = 134) continued to receive usual care.

At the beginning of the trial, the average serum phosphorus level was 7.2 mg/dL among intervention participants and 7.1 mg/dL among control participants. After 3 months, serum phosphorus levels declined by 1.0 mg/dL among intervention participants and by 0.4 mg/dL among control participants, a difference of 0.6 mg/dL. Intervention participants also had significantly larger increases in reading ingredient lists and nutrition facts labels compared with control participants.

"The 0.6-mg/dL larger decline in average phosphorus level among intervention participants compared with control participants corresponds to a 5 percent to 15 percent reduction in relative mortality risk in observational studies," the researchers write.

"Our findings raise the possibility that typical intakes of processed and fast foods contribute to the persistent hyperphosphatemia, cardiovascular events, and bone disease observed among patients with ESRD. Our results have important implications for patients, clinicians, researchers, and policy makers. Patients with ESRD and clinicians should learn about both naturally occurring phosphorus and phosphorus-containing additives, and patients should limit their total phosphorus intake to 800 to 1,000 mg/d as recommended by practice guidelines."

The authors add that researchers should focus on developing more potent approaches to preventing and treating hyperphosphatemia, and policy makers should consider approaches to address this problem, such as mandating that phosphorus content be listed on nutrition facts labels.

"Further work is needed to enhance the potency of our intervention and to understand the impact of phosphorus-containing additives on patients with less severe renal disease and on the general public," the researchers conclude.

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