DALLAS – More than one-third of Americans have a high dietary phosphorus intake and an all-cause mortality rate that is more than double that of Americans with lower dietary phosphorus consumption, based on a large observational study.
High dietary phosphorus density – a value of at least 35 mg/kcal for the product of dietary phosphorus intake divided by total energy intake – was associated with a 2.27-fold increased risk of all-cause mortality and a 3.39-fold elevation in cardiovascular mortality, Dr. Alex R. Chang reported at the American Heart Association scientific sessions.
Dr. Alex R. Chang
The findings came from an analysis of a nationally representative cohort comprising 8,686 adult participants in the Third National Health and Nutrition Examination Survey (NHANES III). Since this was an observational study, the strong association between high phosphorus intake and increased mortality doesn’t prove causality and there is no evidence that reducing phosphorus consumption would reduce mortality. But the study findings do raise public health concerns, given that 35% of Americans consume daily more than 1,400 mg of phosphorus.
That intake level, twice the Recommended Daily Allowance of 700 mg, was associated with a 2.23-fold increased risk of all-cause mortality in an NHANES III multivariate analysis adjusted for demographics, traditional cardiovascular risk factors, estimated glomerular filtration rate, vitamin D status, and total energy intake. Consumption below the 1,400 mg/day threshold was not associated with any increased mortality risk, according to Dr. Chang, a nephrologist at the Geisinger Health System in Danville, Pa.
During a median 14.7 years of follow-up in the study, there were 1,129 deaths, including 384 cardiovascular deaths.
Inorganic phosphates added to processed foods as preservatives are the chief sources of phosphorus in the U.S. diet. A recent study by researchers at Case Western Reserve University, Cleveland, determined that fully 44% of the 2,394 top-selling branded grocery products contain phosphorus additives. The additives were present in 72% of prepared frozen foods, 70% of dry food mixes, 65% of packaged meats, 57% of baked goods, 54% of soups, and 51% of yogurts. Phosphorus-added foods were not only widespread, they cost less than foods free of phosphorus additives (J. Ren. Nutr. 2013;23:265-70).
It’s noteworthy that the inorganic phosphates used in food additives are more bioavailable than the organic phosphorus found naturally in eggs, nuts, and other foods, Dr. Chang said.
Animal studies point to several possible mechanisms that might account for the observed association between high dietary phosphorus and increased mortality in NHANES III, including promotion of vascular calcification, endothelial dysfunction, and increased levels of fibroblast growth factor 23, which is a phosphaturic hormone whose overexpression is linked to left ventricular hypertrophy, progression of chronic kidney disease, and cardiovascular events.
Dr. Chang’s study was supported by the National Institute of Diabetes and Digestive and Kidney Diseases. He reported having no financial conflicts.