Abstract
Hyperkalemia has been associated with higher mortality in long-term hemodialysis (HD) patients. There are few data concerning the relationship between dietary potassium intake and outcome. The mortality predictability of dietary potassium intake from reported food items estimated using the Block Food Frequency Questionnaire (FFQ) at the start of the cohort was examined in a 5-year (2001-2006) cohort of 224 HD patients in Southern California using Cox proportional hazards regression. 224 long-term HD patients from 8 DaVita dialysis clinics. Dietary potassium intake ranking using the Block FFQ. 5-year survival. HD patients with higher potassium intake had greater dietary energy, protein, and phosphorus intakes and higher predialysis serum potassium and phosphorus levels. Greater dietary potassium intake was associated with significantly increased death HRs in unadjusted models and after incremental adjustments for case-mix, nutritional factors (including 3-month averaged predialysis serum creatinine, potassium, and phosphorus levels; body mass index; normalized protein nitrogen appearance; and energy, protein, and phosphorus intake) and inflammatory marker levels. HRs for death across the 3 higher quartiles of dietary potassium intake in the fully adjusted model (compared with the lowest quartile) were 1.4 (95% CI, 0.6-3.0), 2.2 (95% CI, 0.9-5.4), and 2.4 (95% CI, 1.1-7.5), respectively (P for trend = 0.03). Restricted cubic spline analyses confirmed the incremental mortality predictability of higher potassium intake. FFQs may underestimate individual potassium intake and should be used to rank dietary intake across the population. Higher dietary potassium intake is associated with increased death risk in long-term HD patients, even after adjustments for serum potassium level; dietary protein; energy, and phosphorus intake; and nutritional and inflammatory marker levels. The potential role of dietary potassium in the high mortality rate of HD patients warrants clinical trials.
Highlights
Hyperkalemia has been associated with higher mortality in long-term hemodialysis (HD) patients
Greater dietary potassium intake was associated with significantly increased death hazard ratios (HR) in the unadjusted models and after incremental adjustments for case-mix, nutritional factors and inflammatory markers
Higher dietary potassium intake is associated with increased death risk in longterm HD patients, even after adjustments for serum potassium and dietary protein, energy and phosphorus intake and nutritional and inflammatory markers
Summary
Study Design and PopulationWe studied prevalent HD patients who participated in the NIH-funded NIED (Nutritional and Inflammatory Evaluation in Dialysis) Study.[14,15,16,17,18] The original patient cohort was derived from a pool of approximately 1,300 HD outpatients in eight DaVita Inc. chronic dialysis facilities in the South Bay Los Angeles area (the NIED Study website [www.NIEDStudy.org] contains more details). A modified version of the Charlson comorbidity index, i.e. without the age and kidney disease components, was used to assess the severity of comorbidities.[19,20] The survival of these 224 HD patients was followed up to 63 months, i.e., until December 31, 2006. A restricted cubic splines graph was utilized as an exploratory data analysis strategy to illustrate systematic relations between dietary potassium and mortality. This method served to examine the non-linear associations as continuous mortality predictors as an alternative to potential inappropriate assumptions concerning linearity.[35] Thereafter, to calculate the relative risks of death, hazard ratios (HR) were obtained using Cox proportional hazard models after controlling for the relevant covariates. Descriptive and multivariate statistics were carried out with the statistical software Stata version 10 (Stata Corp, www.stata.com)
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