An excessive amount of dietary phosphorus can be dangerous for people with moderate to severe kidney disease, according to a recent U.S. study.

Patients with moderate to severe kidney disease have trouble excreting phosphorus which can lead to a buildup of the chemical. An elevated level of phosphorus in the blood (hyperphosphatemia) increases the risk of illness or death.

To reduce this risk, kidney patients are advised to limit eating foods that are naturally high in phosphorus, such as meats, dairy products, whole grains and nuts. Cereals, multi-grain breads and peanut butter are three products that list phosphorus.

In its background information for the study, though, researchers found that phosphorus-containing additives are now being added to processed and fast foods. But not all food products list phosphorus on the nutrition label and it is not mandatory to do so.

The study included 279 patients with end-stage renal disease (ESRD) with serum (blood) levels of phosphorus greater than 5.5 milligrams per deciliter (mg/dL). Then, 145 of the patients received education on avoiding foods with phosphorus additives when purchasing groceries or when at a fast-food restaurant while 134 of the patients continued to receive the usual care.

When the study started, the average serum phosphorus level was 7.2 mg/dL in the intervention group and 7.1 mg/dL in the control group. After three months, the levels in the intervention group declined by 1.0 mg/dL while the levels in the control group went down by 0.4 mg/dL.

The research team point out that the 0.6 mg/dL larger decline in average phosphorus levels for the intervention group compared with the control group relates to a 5 to 15 per cent reduction in relative mortality risk in observational studies.

The researchers add that the findings raise the possiblity that typical intakes of processed and fast foods contribute to the persistent hyperphosphatemia, cardiovascular events and bone disease among ESRD patients. They suggest that patients with ESRD and clinicians should learn about both naturally occurring phosphorus and phosphorus-containing additives and that patients should limit their total phosphorus intake to 800 to 1,000 milligrams per day.

The team hoped that policy makers would consider making it mandatory to list the phosphorus content on nutrition labels.