Reference
Moore LW, Nolte JV, Gaber AO, Suki WN. Association of dietary phosphate and serum phosphorus concentration by levels of kidney function. Am J Clin Nutr. 2015;102(2):444-453.
Objective
To examine the relationship between dietary phosphorus intake—from both organic and inorganic sources—and serum phosphorus concentration in a large cohort of healthy subjects and subjects with reduced kidney function.
Design
This study was a cross-sectional evaluation of subjects’ serum phosphorus concentration compared with clinical characteristics and dietary intake reported for the 24-hour period before blood draw.
Participants
The subjects were 7,895 adult participants (aged 20 to 85 years) in the National Health and Nutrition Examination Survey 2003-2006, who were not pregnant and for whom 24-hour dietary recall information and laboratory values for serum creatinine and phosphorus, urine creatinine, and albumin were available.
Parameters Assessed
Dietary phosphorus in foods and supplements, as well as its source (organic phosphorus compared with inorganic phosphate additives); socioeconomic status, (level of education and level of family income); fasting serum creatinine and phosphorus; urine albumin and creatinine; kidney function [estimated glomerular filtration rate (eGFR); albumin to creatinine ratio (ACR); body mass index (BMI)]
Primary Outcome Measures
The average age of participants was 46.7; 52.8% were Caucasian; mean BMI was 28.4; 33.4% were obese. Hypertension was present in 41.6%; 11.8% had elevated serum glucose; the mean ACR was 27.7 mg/g. Groups with a lower level of kidney function contained a higher proportion male subjects, were older in age, and had a higher prevalence of hypertension and hyperglycemia. The population median serum phosphorus was 3.73 mg/dL (range, 1.9–6.8 mg/dL) and varied by level of kidney function.
Key Findings
As expected, those with an eGFR<30 mL/min/1.73 m2 had significantly higher serum phosphorus than those with eGFR>105 mL/min/1.73 m2 (4.12±0.07 vs 3.83±0.02, P=0.0009).
Those who were underweight (BMI<18.5) had higher serum phosphorous concentrations than those who were normal weight (P=0.003). Those who were overweight (BMI 25-29.9) or obese (BMI>30) had lower serum phosphorus (P=0.0007).
Dairy consumption was associated with higher serum phosphorus. Each serving of dairy with inorganic phosphates added led to 0.07 mg/dL incremental increases in phosphorus (P=0.0098). For dairy without added inorganic phosphorus, a 0.02 mg/dL increase in serum phosphorus would occur (P=0.0002).
Each serving of cereals/grains that had added inorganic phosphates led to a small but significant increase in serum phosphorus (0.005 mg/dL, P=0.0084).
Neither education level nor income level correlated with serum phosphorus, in contrast to earlier studies in which lower socioeconomic status was associated with higher serum phosphorous.
Practice Implications
Serum phosphorus, even within the normal range, is associated with cardiovascular events, cardiovascular mortality, and all-cause mortality in healthy subjects as well as patients with chronic kidney disease.1 Excessive phosphorus consumption has been clearly associated with cardiovascular disease, osteoporosis, and all-cause mortality in the general, healthy population.2
In regards to the phosphorus content of the food supply, current nutrient databases are incomplete, and, for the processed foods covered, are thought to underestimate the amount of phosphates by at least 30% because phosphate additives are considered GRAS (generally recognized as safe), and the FDA does not require food manufacturers to provide the amounts of phosphate additives on the fool label.3 Unlike organic phosphate, for which bioavailability ranges from 40% (plant sources) to 60% (animal sources), phosphate additives are 90% to 100% absorbed.4
Excessive phosphorus consumption has been clearly associated with cardiovascular disease, osteoporosis, and all-cause mortality in the general, healthy population.
This study by Moore et al further confirms that phosphate additives in commonly consumed foods, specifically dairy foods, cereals, and grains, significantly increase serum phosphate levels, thus increasing risk of cardiovascular disease, kidney disease, osteoporosis, and all-cause mortality in the “healthy” population. Although their amounts are not specified on food labels, phosphate additives must be listed, and patients should be counseled to minimize their intake of products containing them. For a patient-friendly food list, see the table “Where the Phosphates Lurk and How to Identify Them” in the author’s article, “Canaries in the Phosphate-Toxicity Coal Mines.”5
