Increased Dietary Sodium is Independently Associated With Greater Mortality Among Prevalent Hemodial
Increased Dietary Sodium is Independently Associated With Greater Mortality Among Prevalent Hemodialysis Patients
Dietary sodium is thought to play a major role in the pathogenesis of hypertension, hypervolemia, and mortality in hemodialysis patients; hence, sodium restriction is almost universally recommended. Since the evidence upon which to base these assumptions is limited, we undertook a post-hoc analysis of 1770 patients in the Hemodialysis Study with available dietary, clinical, and laboratory information. Within this cohort, 772 were men, 1113 black, and 786 diabetic, with a mean age of 58 years and a median dietary sodium intake of 2080 mg/day. After case-mix adjustment, linear regression modeling found that higher dietary sodium was associated with a greater ultrafiltration requirement, caloric and protein intake; sodium to calorie intake ratio was associated with a greater ultrafiltration requirement; and sodium to potassium ratio was associated with higher serum sodium. No indices were associated with the pre-dialysis systolic blood pressure. Cox regression modeling found that higher baseline dietary sodium and the ratio of sodium to calorie or potassium were each independently associated with greater all-cause mortality. No association between a prescribed dietary sodium restriction and mortality were found. Thus, higher reported dietary sodium intake is independently associated with greater mortality among prevalent hemodialysis patients. Randomized trials will be necessary to determine whether dietary sodium restriction improves survival.
Sodium restriction has been a central tenet for management of hemodialysis patients since renal replacement therapy first became available. Total body sodium is a critical determinant of extracellular volume, plasma volume, and blood pressure. Under conditions of health, sodium balance is tightly regulated, principally through natriuresis. However, in oligo-anuric hemodialysis subjects, renal sodium excretion is severely impaired, and the hemodialysis procedure must provide for requisite sodium and water removal.
Previous studies in hemodialysis subjects have suggested that dietary salt restriction is associated with reduced inter-dialytic weight gain (IDWG), lesser requirement for anti-hypertensive medication, and ameliorative effects on left ventricular hypertrophy. It has therefore been recommended that hemodialysis patients carefully restrict sodium intake, with the belief that this leads to improved volume and blood pressure control, and ultimately survival. However, in peritoneal dialysis, there is evidence that lower dietary sodium may actually be associated with higher mortality. One potential explanation for this finding is that, because sodium and caloric intake are highly correlated, the fluid homeostatic benefits of salt restriction are outweighed by unintended concomitant nutritional compromise.
Overall, prior studies in hemodialysis patients have been limited by small size, lack of prospectively collected data, limited follow-up, and consideration of only surrogate end points. To our knowledge, there has been no directed study of the association between dietary sodium intake and mortality. To address these limitations, we conducted a post-hoc analysis of the Hemodialysis (HEMO) Study, a large-scale, prospective trial with detailed dietary assessments. We examined the associations of reported dietary sodium (diet-Na) intake with ultrafiltration (UF) requirement, systolic blood pressure (SBP), nutritional indices, and all-cause mortality. In an attempt to further delineate the macronutrient-independent associations of dietary sodium intake with all-cause mortality, we performed analogous analyses considering sodium:calorie intake ratio (Na:Cal) and sodium:potassium intake ratio (Na:K) as the exposures of interest. Finally, we considered prescribed sodium restriction to explore the potential clinical effectiveness of advice regarding dietary sodium intake on outcomes.
Abstract and Introduction
Abstract
Dietary sodium is thought to play a major role in the pathogenesis of hypertension, hypervolemia, and mortality in hemodialysis patients; hence, sodium restriction is almost universally recommended. Since the evidence upon which to base these assumptions is limited, we undertook a post-hoc analysis of 1770 patients in the Hemodialysis Study with available dietary, clinical, and laboratory information. Within this cohort, 772 were men, 1113 black, and 786 diabetic, with a mean age of 58 years and a median dietary sodium intake of 2080 mg/day. After case-mix adjustment, linear regression modeling found that higher dietary sodium was associated with a greater ultrafiltration requirement, caloric and protein intake; sodium to calorie intake ratio was associated with a greater ultrafiltration requirement; and sodium to potassium ratio was associated with higher serum sodium. No indices were associated with the pre-dialysis systolic blood pressure. Cox regression modeling found that higher baseline dietary sodium and the ratio of sodium to calorie or potassium were each independently associated with greater all-cause mortality. No association between a prescribed dietary sodium restriction and mortality were found. Thus, higher reported dietary sodium intake is independently associated with greater mortality among prevalent hemodialysis patients. Randomized trials will be necessary to determine whether dietary sodium restriction improves survival.
Introduction
Sodium restriction has been a central tenet for management of hemodialysis patients since renal replacement therapy first became available. Total body sodium is a critical determinant of extracellular volume, plasma volume, and blood pressure. Under conditions of health, sodium balance is tightly regulated, principally through natriuresis. However, in oligo-anuric hemodialysis subjects, renal sodium excretion is severely impaired, and the hemodialysis procedure must provide for requisite sodium and water removal.
Previous studies in hemodialysis subjects have suggested that dietary salt restriction is associated with reduced inter-dialytic weight gain (IDWG), lesser requirement for anti-hypertensive medication, and ameliorative effects on left ventricular hypertrophy. It has therefore been recommended that hemodialysis patients carefully restrict sodium intake, with the belief that this leads to improved volume and blood pressure control, and ultimately survival. However, in peritoneal dialysis, there is evidence that lower dietary sodium may actually be associated with higher mortality. One potential explanation for this finding is that, because sodium and caloric intake are highly correlated, the fluid homeostatic benefits of salt restriction are outweighed by unintended concomitant nutritional compromise.
Overall, prior studies in hemodialysis patients have been limited by small size, lack of prospectively collected data, limited follow-up, and consideration of only surrogate end points. To our knowledge, there has been no directed study of the association between dietary sodium intake and mortality. To address these limitations, we conducted a post-hoc analysis of the Hemodialysis (HEMO) Study, a large-scale, prospective trial with detailed dietary assessments. We examined the associations of reported dietary sodium (diet-Na) intake with ultrafiltration (UF) requirement, systolic blood pressure (SBP), nutritional indices, and all-cause mortality. In an attempt to further delineate the macronutrient-independent associations of dietary sodium intake with all-cause mortality, we performed analogous analyses considering sodium:calorie intake ratio (Na:Cal) and sodium:potassium intake ratio (Na:K) as the exposures of interest. Finally, we considered prescribed sodium restriction to explore the potential clinical effectiveness of advice regarding dietary sodium intake on outcomes.
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