Dietary potassium intake and mortality in long-term hemodialysis patients

Abstract

Background: 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.

Study design: 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.

Setting & participants: 224 long-term HD patients from 8 DaVita dialysis clinics.

Predictors: Dietary potassium intake ranking using the Block FFQ.

Outcomes: 5-year survival.

Results: 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.

Limitations: FFQs may underestimate individual potassium intake and should be used to rank dietary intake across the population.

Conclusions: 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.

Figure 1

Scatter plots with regression lines reflecting the correlations between potassium intake with calorie (upper, left), protein (upper right) and phosphorus intakes (lower left) and baseline predialysis serum potassium (lower right). Shaded areas reflect the 95% confidence intervals.

Figure.2

Spline model with 95% CI and 2 degree of freedom reflecting adjusted mortality predictability of potassium intake, expressed as a percentile of the average dietary potassium intake in the 224 maintenance hemodialysis patients (from Oct. 2001 to Jan. 2007). A parsimonious model with a limited number of adjusters (case mix, serum potassium and intakes of energy, protein and phosphorus) has been examined here. Estimated daily potassium intake in mmoles (mean+/−SD) is shown for each quartile (Q). Estimates is based on a food frequency questionnaire, which tends to underestimate daily nutrient intake proportionately, including daily potassium intake.

Figure 3

Kaplan-Meier proportion of surviving HD patients after 5 years of observation according to the quartiles of potassium intake in 224 HD patients,adjusted for case-mix.Case-mix variables: age, gender, race/ethnicity, diabetes mellitus, dialysis vintage, primary insurance, marital status, Charlson co-morbidity score, dialysis dose (Kt/V), intake of phosphorus binders and residual renal function.