Micronutrition in dialysis

Dietary micronutrient intake in peritoneal dialysis patients: relationship with nutrition and inflammation status

OBJECTIVE

To compare dietary intake of micronutrients by peritoneal dialysis (PD) patients according to their nutrition and inflammatory statuses.

DESIGN

This cross-sectional study evaluated 73 patients using subjective global assessment, 24-hour dietary recall, and markers of inflammation [C-reactive protein (CRP), tumor necrosis factor α, and interleukin 6].

RESULTS

Half the patients had an inadequate micronutrient intake. Compared with dietary reference intakes, malnourished patients had lower intakes of iron (11 mg) and of vitamins C (45 mg) and B6 (0.8 mg). Malnourished and well-nourished patients both had lower intakes of sodium (366 mg, 524 mg respectively), potassium (1555 mg, 1963 mg), zinc (5 mg, 7 mg), calcium (645 mg, 710 mg), magnesium (161 mg, 172 mg), niacin (8 mg, 9 mg), folic acid (0.14 mg, 0.19 mg), and vitamin A (365 μg, 404 μg). Markers of inflammation were higher in malnourished than in well-nourished subjects. Compared with patients in lower quartiles, patients in the highest CRP quartile had lower intakes (p < 0.05) of sodium (241 mg vs 404 mg), calcium (453 mg vs 702 mg), vitamin B2 (0.88 mg vs 1.20 mg), and particularly vitamin A (207 μg vs 522 μg).

CONCLUSIONS

Among PD patients, half had inadequate dietary intakes of iron, zinc, calcium and vitamins A, B6, C, niacin, and folic acid. Lower micronutrient intakes were associated with malnutrition and inflammation. Patients with inflammation had lower intakes of sodium, calcium, and vitamins A and B2. Micronutrient intake must be investigated in various populations so as to tailor adequate supplementation.

Racial group differences in plasma concentrations of antioxidant vitamins and carotenoids in hemodialysis patients

Approximately 50% of the mortality in hemodialysis patients is due to cardiovascular disease. Antioxidant vitamins and carotenoids may be protective because oxidation of low-density lipoproteins appears to be a necessary prerequisite for the development of atherogenesis, and hemodialysis itself may stimulate the generation of oxygen reactive species. African Americans comprise a substantial proportion of dialysis patients because they have higher rates of hypertension, glomerulonephritis, and diabetic end-stage renal disease than do whites. The purpose of this cross-sectional study was to determine the plasma concentrations of antioxidant vitamins and carotenoids in hemodialysis patients and to investigate whether differences in these concentrations in the major racial or ethnic groups exist. Plasma concentrations of alpha- and gamma-tocopherol, carotenoids, and retinol were measured with HPLC and plasma vitamin C was measured with a spectrophotometric method in 109 white and African American hemodialysis patients. Dietary intakes of selected micronutrients were also compared by using data from a food-frequency questionnaire. Overall, plasma vitamin C and alpha-tocopherol concentrations were comparable but plasma carotenoid concentrations were lower than those reported for other populations. African American patients had significantly higher mean plasma concentrations of retinol (P < 0.04), lutein (P < 0.02), and total carotenoids minus lycopene (P < 0.04); whites had significantly higher mean plasma concentrations of alpha-tocopherol (P < 0.02), independent of age and plasma lipid concentrations. Diabetes comorbidity had an independent negative association with plasma beta-carotene concentration but was not associated with other measures.

Vitamin B6 and hemodialysis: the impact of high-flux/high-efficiency dialysis and review of the literature

High-flux/high-efficiency (HF/HE) dialysis is associated with improved clearance for larger molecules, which include a wide variety of middle molecules and water-soluble vitamins. Our study attempted to measure in vivo clearances of serum pyridoxal-5'-phosphate (PLP), the active metabolite of vitamin B6, on standard cuprophan versus cellulose triacetate HF/HE dialysis for patients maintained on 10 mg daily pyridoxine supplements. A longitudinal evaluation of PLP after 3 months on HF/HE dialysis was performed simultaneously. The average in vivo PLP clearance for six patients on standard hemodialysis increased by more than 50%, from 86 +/- 61.7 mL/min using a cuprophan membrane to 173 +/- 90.2 mL/min using a cellulose triacetate dialyzer, at average blood flows of 375 mL/min (P < 0.05). Levels of PLP decreased from a baseline of 50 +/- 13.8 ng/mL to 24 +/- 9.7 ng/mL (P < 0.05) after 3 months of HF/HE treatments; the levels returned to 45 +/- 6.4 ng/mL on resumption of standard dialysis treatments. Although not achieving statistical significance, the average hematocrit increased from 31.2% +/- 1.66% to 32.7% +/- 1.24% while on HF/HE dialysis without an increase in erythropoietin requirements. We conclude that HF/HE dialysis treatments can have a dramatic impact on vitamin B6 homeostasis. Further investigation to evaluate the effects of different membranes and reprocessing should be performed on more heterogeneous patient populations in whom compliance problems with diet and vitamin supplementation may exist. The increased clearance of vitamin B6 may have significantly more detrimental effects in these settings.