Association of dietary phosphate and serum phosphorus concentration by levels of kidney function.

BACKGROUND The health implications of dietary phosphorus intake and the role of kidney function in managing serum phosphorus homeostasis are well studied. However, examining the source of dietary phosphorus intake and its impact on serum phosphorus has not been characterized in population studies. OBJECTIVE This study aimed to distinguish the association of food sources of organic phosphorus and inorganic phosphate additives with serum phosphorus concentration. DESIGN A cross-sectional analysis of 24-h food recall data from 7895 adult participants in the National Health and Nutrition Examination Survey 2003-2006 was performed. Phosphorus content of foods was categorized as organic or inorganic. Correlations of serum phosphorus to clinical and dietary intake variables were achieved by using multiple regression analysis. RESULTS After controlling for estimated glomerular filtration rate (eGFR), body mass index (BMI; in kg/m²), and albumin-to-creatinine ratio, a significant increase in serum phosphorus occurred with dairy foods with inorganic phosphates [parameter estimate (PE) ± SE: 0.07 ± 0.02 mg/dL, P < 0.01] or without inorganic phosphates (PE: 0.02 ± 0.01, P < 0.001) and cereals/grains with inorganic phosphates (PE: 0.005 ± 0.002, P < 0.01). Significantly higher serum phosphorus occurred when eGRF was <30 (PE: 0.24 ± 0.08, P < 0.0001), but eGFR 30-44 (PE: -0.11 ± 0.04, P < 0.01) and 45-60 (PE: -0.10 ± 0.04, P < 0.01) were associated with lower serum phosphorus; higher serum phosphorus was associated with BMI <18.5 (PE: 0.18 ± 0.05, P = 0.0009) but lower with BMI ≥35-39 (PE: -0.09 ± 0.03, P = 0.0013) or ≥40 (PE: -0.10 ± 0.03, P = 0.014). CONCLUSIONS This analysis shows that dairy products and cereals/grains having inorganic phosphate additives significantly increase serum phosphorus concentration, despite being consumed less frequently than foods without phosphate additives. It seems prudent for the Nutrient Facts Label to include phosphorus but also for food manufacturers to consider alternatives to phosphate additives.