THURSDAY, Nov. 5 (HealthDay News) -- Elevated blood levels of phosphorus are associated with a higher risk of heart disease, U.S. researchers say.

They studied the link between phosphorus levels and coronary artery calcification (CAC) in nearly 900 healthy adults in the Spokane Heart Study, a long-term investigation of heart disease risk factors. CAC is an early sign of hardening of the arteries.

At the start of the study, 28 percent of participants had CAC. After six years of follow-up, another 33 percent had developed CAC, and the level of CAC increased among those who already had the condition.

The association between phosphorus levels and CAC was strong even after the researchers adjusted for other factors.

"Even small increases in the blood level of phosphorus predicted an increased risk of progressive CAC in these apparently healthy adults," Dr. Katherine R. Tuttle, of the Providence Medical Research Center in Spokane, said in a news release.

The researchers also found that people with lower kidney function -- even if not below the normal range -- were more likely to have progressive CAC.

"Our results may help to explain why even early-stage chronic kidney disease (CKD) is associated with increased cardiovascular risk that is not explained by traditional risk factors," Tuttle said. "More research will be needed to see if treatments to lower phosphorus levels can reduce heart disease risk in people with early-stage CKD, or even those without CKD who have CAC."

The study was published online Nov. 5 in advance of print publication in the December issue of the Clinical Journal of the American Society of Nephrology.

More information

The U.S. National Heart, Lung, and Blood Institute has more about heart disease risk factors.