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Phosphorus additives pose ‘hidden’ danger to kidney patients

By Stephen Daniells , 11-Feb-2009

Patients with kidney disease may be at danger from a ‘hidden threat’ of phosphorous additives found in processed and fast foods, says a new study from the US.

Writing in the new issue of the Journal of the American Medical Association (JAMA), Ohio-based scientists report that additional phosphorous, such as sodium phosphate or pyrophosphate, may be too much for a compromised kidney to expel.

The additives are used to enhance flavour and shelf life, particularly in meats, cheeses, baked goods, and beverages, said the researchers from MetroHealth Medical Center and Case Western Reserve University School of Medicine in Cleveland.

Certain foods, such as meats, dairy products, whole grains, and nuts, naturally contain high levels of phosphorous, and patients with advanced kidney disease are recommended to avoid these foods. Increased levels of the mineral in the blood can lead to heart disease, bone disease, and may even be fatal for patients with advanced kidney disease.

"Phosphorus is already abundant in naturally-occurring foods," explained co-researcher Srilekha Sayre. "By adding even more phosphorus to our food supply, we may be exceeding the body's regulatory ability, especially for those with kidney disease.

“We need to limit the use of these additives until their impact is better understood or at least encourage the Food and Drug Administration to require food manufacturers to report phosphorus content on nutrition food labels."

Study details

The Ohio-based researchers randomly assigned 279 people with advanced kidney disease receiving dialysis treatment to one of two groups: One group acted as the control, and received usual care. The second group was taught to avoid additive-containing foods when purchasing groceries or eating at fast food restaurants. At the start of the study, all of the participants had high phosphorus blood levels, defined as at least 5.5 milligrams of phosphorous per decilitre.

Three months later the researchers found that the blood levels of phosphorus in the intervention group had decreased by two and a half times more than in the control group (0.4 versus 1.0 mg/dL, repsectively).

“The 0.6 mg/dL larger decline in average phosphorus level among intervention participants compared with control participants corresponds to a 5 to 15 per cent reduction in relative mortality risk in observational studies,” wrote the researchers.

“Our intervention has the advantages of being simple, low-cost, and easy to implement.”

Policy implications

The researchers said that the results have implications for manufacturers and policy makers. The latter should consider both the cost of policy approaches to address the problem of phosphate additives in foods, and the related health care costs associated with high phosphorus intake and hyperphosphatemia.

“Policy approaches may include mandating that phosphorus content be listed on nutrition facts labels (as calories, fat, and sodium already are),” wrote the researchers. “Although manufacturers may voluntarily include phosphorus content on such labels, most foods do not have this information.”

“It is worth noting that many manufacturers eliminated or greatly reduced the trans fat content of their products in response to a recent mandate to include trans fat on nutrition facts labels. Other approaches may involve creating incentives for producing and marketing low-phosphorus products and funding alternatives to phosphorus-containing additives.”

Source: Journal of the American Medical Association
Volume 301, Issue 6, Pages 629-635
“Effect of Food Additives on Hyperphosphatemia Among Patients With End-stage Renal Disease: A Randomized Controlled Trial”
Authors: C. Sullivan, S.S. Sayre, J.B. Leon, R. Machekano, T.E. Love, D. Porter, M. Marbury, A.R. Sehgal

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