The Interplay between Dietary Phosphorous, Protein Intake, and Mortality in a Prospective Hemodialysis Cohort.

(1) Background: Current dietary recommendations for dialysis patients suggest that high phosphorus diets may be associated with adverse outcomes such as hyperphosphatemia and death. However, there has been concern that excess dietary phosphorus restriction may occur at the expense of adequate dietary protein intake in this population. We hypothesized that higher dietary phosphorus intake is associated with higher mortality risk among a diverse cohort of hemodialysis patients. (2) Methods: Among 415 patients from the multi-center prospective Malnutrition, Diet, and Racial Disparities in Kidney Disease Study, we examined the associations of absolute dietary phosphorus intake (mg/day), ascertained by food frequency questionnaires, with all-cause mortality using multivariable Cox models. In the secondary analyses, we also examined the relationship between dietary phosphorus scaled to 1000 kcal of energy intake (mg/kcal) and dietary phosphorus-to-protein ratio (mg/g) with survival. (3) Results: In expanded case-mix + laboratory + nutrition adjusted analyses, the lowest tertile of dietary phosphorus intake was associated with higher mortality risk (ref: highest tertile): adjusted HR (aHR) (95% CI) 3.33 (1.75-6.33). In the analyses of dietary phosphorus scaled to 1000 kcal of energy intake, the lowest tertile of intake was associated with higher mortality risk compared to the highest tertile: aHR (95% CI) 1.74 (1.08, 2.80). Similarly, in analyses examining the association between dietary phosphorus-to-protein ratio, the lowest tertile of intake was associated with higher mortality risk compared to the highest tertile: aHR (95% CI) 1.67 (1.02-2.74). (4) Conclusions: A lower intake of dietary phosphorus was associated with higher mortality risk in a prospective hemodialysis cohort. Further studies are needed to clarify the relationship between specific sources of dietary phosphorus intake and mortality in this population.

Serum albumin is incrementally associated with increased mortality across varying levels of kidney function.

OBJECTIVES: Serum albumin (sAlb) may be a strong predictor of longevity in the general population and in chronic kidney disease. This study aimed to determine the relationship between sAlb concentrations and mortality risk independent of kidney function. METHODS: This was a retrospective cohort study of 31 274 adults from the 1999-2010 National Health and Nutrition Examination Survey. The estimated glomerular filtration rate (eGFR) was examined as both a confounder and modifier of the association of sAlb with mortality risk. We examined the association of sAlb (categorized as <3.8, 3.8 to <4.0, 4.0 to <4.2, 4.2 to <4.4, 4.4 to <4.6, 4.6 to <4.8, and ≥4.8 g/dL) with mortality using Cox models. Subsequently, we conducted spline analyses to estimate the association of sAlb with all-cause mortality across varying eGFR levels. RESULTS: In unadjusted analyses, participants with incrementally lower sAlb concentrations of <4.6 g/dL had an increasingly higher mortality risk compared with those with sAlb levels ranging from 4.6 to <4.8 g/dL (reference), whereas those with higher sAlb levels of ≥4.8 g/dL had a lower mortality risk (hazard ratios [95% confidence interval]: 3.88 [3.26-4.62], 3.59 [3.01-4.27], 2.79 [2.37-3.29], 2.10 [1.79-2.48], 1.72 [1.45-2.03], and 0.71 [0.55-0.92] for sAlb concentrations of <3.8, 3.8 to <4.0, 4.0 to <4.2, 4.2 to <4.4, 4.4 to <4.6, and ≥4.8 g/dL, respectively). Adjusted analyses showed similar findings, although the association of higher sAlb levels of ≥4.8 g/dL with better survival was attenuated to the null. Spline analyses showed that participants with sAlb levels of <4.6 g/dL had higher mortality across all concentrations of eGFR, ranging from 30 to 120 mL/min/1.73 m2 (reference: sAlb ≥ 4.6 g/dL). CONCLUSIONS: Among a nationally representative U.S. cohort, a graded association was observed between lower sAlb concentrations and higher death risk, which was robust across varying levels of kidney function.