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Is calcium endangering dialysis patients?

Study finds a possible link to heart disease

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WASHINGTON — A sad irony of kidney failure is that the top killer of people on dialysis is not their kidneys — it's heart disease.

Kidney patients are up to 30 times more likely than the general population to die from heart disease, and doctors don't understand why their hearts are so vulnerable.

Now surprising new research reveals even very young kidney patients — those who need dialysis in their 20s — can have heart arteries so damaged they resemble a 60-year-old's. And the California researchers have sparked controversy by arguing that a standard treatment might be part of the problem.

It's a "therapeutic dilemma that we face every day," contends Dr. William Goodman of the University of California, Los Angeles.

At issue is whether the super-high doses of calcium needed by most of the nation's 250,000 dialysis patients to help their kidneys also dangerously harden their arteries.

Goodman thinks they can, and he now prescribes a new calcium-free kidney treatment called Renagel for certain high-risk patients.

But the National Kidney Foundation says the issue is far from settled, and Goodman's research instead may illustrate how dialysis patients can damage their hearts by not adhering to special kidney diets.

"Should there be concern (about calcium)? Yes," says foundation spokesman Dr. George Bakris of Rush-Presbyterian-St. Luke's Medical Center in Chicago.

But the worse a patient's diet, the more calcium pills he or she needs to lower the resulting phosphorus in their bodies — and high phosphorus may be the real culprit, Bakris says. So "the real take-home message is . . . you may die from coronary disease if you don't comply" with a kidney-healthy diet.

(If you have healthy kidneys, don't worry. The calcium doses at issue here are far above the roughly 1,000 milligrams a day most Americans need for healthy bones.)

Goodman and fellow UCLA nephrologist Dr. Isidro Salusky used powerful new imaging technology to scan the arteries of 39 young dialysis patients. Nearly 90 percent of those in their 20s had serious coronary artery calcification.

Calcium deposits had crystallized in their arteries, a form of cardiovascular disease virtually unheard of in young people. You'd expect that in 60- or 70-year-olds.

That shook nephrologists, who knew older patients had stiff arteries but hadn't considered young patients at risk. "These are very, very important findings," says National Institutes of Health kidney chief Dr. Josephine Briggs.

But the study, recently published in the New England Journal of Medicine, triggered controversy for another reason: Patients with the stiffest arteries ingested a stunning 6,000 milligrams of calcium a day, twice as much as kidney patients whose arteries weren't calcified.

Diseased kidneys can't process phosphorus from such foods as dairy products. The more phosphorus patients eat, the more calcium pills they need to sop up and dispose of phosphorus through the intestines. Other drugs are supposed to keep patients' blood from absorbing too much calcium.

"We may well be producing calcium toxicity," Goodman says. But he acknowledges, "I don't have definitive proof" — the study is too small.

There is one calcium-free phosphate treatment. Renagel hit the market almost two years ago. But specialists have been slow to embrace it because patients require up to twice as many Renagel capsules as calcium tablets, at about 51 cents a capsule compared with pennies for calcium, says Goodman.

As a compromise, Goodman gives patients a mix of the two therapies, lowering calcium without having to pay for full regimens of Renagel.

Bakris cautions that Renagel and calcium must be compared directly for proof.

Regardless of how the controversy resolves, the NIH's Briggs says it's a good opportunity to remind all kidney patients they're at high risk of a heart attack — and thus must pay extra attention to lowering blood pressure and cholesterol, exercising and avoiding tobacco.

On the Internet

New England Journal of Medicine abstract of article: www.nejm.org/content/2000/0342/0020/1478.asp

National Kidney Foundation: www.kidney.org/