Longitudinal follow-up of chronic hemodialysis patients without vitamin supplementation

Water-soluble vitamins and trace elements in children with chronic kidney disease stage 5d

Children receiving maintenance dialysis (chronic kidney disease (CKD) stage 5d) have unique risk factors for micronutrient deficiency or toxicity. Children receiving chronic dialysis often require specialized diet plans that may provide more than the recommended daily allowance (RDA) of water-soluble vitamins and micronutrients, with or without the addition of a kidney-friendly vitamin. The following is a comprehensive review of current literature on disorders of micronutrients in this population including those of water-soluble vitamins (vitamin C and vitamin B complexes) and trace elements (copper, selenium, and zinc) and has three areas of focus: (1) the risk factors and clinical presentations of disorders of micronutrients, both deficiency and toxicity, (2) the tools to evaluate micronutrient status, and (3) the central role of renal dietitians in optimizing nutritional status from a micronutrient perspective.

Extracorporeal treatment for ethylene glycol poisoning: systematic review and recommendations from the EXTRIP workgroup

Ethylene glycol (EG) is metabolized into glycolate and oxalate and may cause metabolic acidemia, neurotoxicity, acute kidney injury (AKI), and death. Historically, treatment of EG toxicity included supportive care, correction of acid-base disturbances and antidotes (ethanol or fomepizole), and extracorporeal treatments (ECTRs), such as hemodialysis. With the wider availability of fomepizole, the indications for ECTRs in EG poisoning are debated. We conducted systematic reviews of the literature following published EXTRIP methods to determine the utility of ECTRs in the management of EG toxicity. The quality of the evidence and the strength of recommendations, either strong ("we recommend") or weak/conditional ("we suggest"), were graded according to the GRADE approach. A total of 226 articles met inclusion criteria. EG was assessed as dialyzable by intermittent hemodialysis (level of evidence = B) as was glycolate (Level of evidence = C). Clinical data were available for analysis on 446 patients, in whom overall mortality was 18.7%. In the subgroup of patients with a glycolate concentration ≤ 12 mmol/L (or anion gap ≤ 28 mmol/L), mortality was 3.6%; in this subgroup, outcomes in patients receiving ECTR were not better than in those who did not receive ECTR. The EXTRIP workgroup made the following recommendations for the use of ECTR in addition to supportive care over supportive care alone in the management of EG poisoning (very low quality of evidence for all recommendations): i) Suggest ECTR if fomepizole is used and EG concentration > 50 mmol/L OR osmol gap > 50; or ii) Recommend ECTR if ethanol is used and EG concentration > 50 mmol/L OR osmol gap > 50; or iii) Recommend ECTR if glycolate concentration is > 12 mmol/L or anion gap > 27 mmol/L; or iv) Suggest ECTR if glycolate concentration 8-12 mmol/L or anion gap 23-27 mmol/L; or v) Recommend ECTR if there are severe clinical features (coma, seizures, or AKI). In most settings, the workgroup recommends using intermittent hemodialysis over other ECTRs. If intermittent hemodialysis is not available, CKRT is recommended over other types of ECTR. Cessation of ECTR is recommended once the anion gap is < 18 mmol/L or suggested if EG concentration is < 4 mmol/L. The dosage of antidotes (fomepizole or ethanol) needs to be adjusted during ECTR.

Water-soluble vitamins in people with low glomerular filtration rate or on dialysis: a review

People with low glomerular filtration rate and people on dialysis are spontaneously at risk for vitamin deficiency because of the potential for problems with decreased appetite and decreased sense of smell and taste, leading to decreased intake, and because decreased energy or decreased cognitive ability results in difficulties in shopping and cooking. Imposed dietary restrictions because of their renal dysfunction and because of comorbidities such as hypertension and diabetes exacerbate this problem. Finally, particularly for water-soluble vitamins, loss may occur into the dialysate. We did not identify any randomized trials of administering daily doses close to the recommended daily allowances of these vitamins. In people who are eating at all, deficiencies of B5 and B7 seem unlikely. It is unclear whether supplements of B2 and B3 are necessary. Because of dialyzability and documented evidence of insufficiency in dialysis patients, B1 supplementation is likely to be helpful. B6, B9, and B12 are implicated in the hyperhomocysteinemia observed in patients on dialysis. These vitamins have been studied in combinations, in high doses, with the hope of reducing cardiovascular outcomes. No reductions in patient-important outcomes were seen in adequately powered randomized trials. Because of their involvement in the homocysteine pathway, however, supplementation with lower doses, close to the recommended daily allowances, may be helpful. Vitamin C deficiency is common in patients on dialysis who are not taking supplements: low-dose supplements are warranted. Vitamins for dialysis patients contain most or all of the B vitamins and low-dose vitamin C. We are not aware of any medical reasons to choose one over another.

Water-soluble vitamin levels in extended hours hemodialysis

Patients on extended hours (>15 h/week) hemodialysis may be at a higher risk of deficiency of water-soluble vitamins than conventional (≤15 h/week) hemodialysis patients due to their increased weekly hours of dialysis. We compared serum levels of the water-soluble vitamins in a group of extended and conventional hours hemodialysis patients. Predialysis serum levels of vitamin C, vitamin B12, thiamine, pyridoxine, and folate were measured in 52 patients: 26 extended group and 26 conventional group. Information on patient's intake of vitamin supplements and dialysis regimen was obtained. Data were log transformed due to the skewed distribution of the results. Median vitamin C levels were significantly lower in the extended group (0.30 vs. 1.14 mg/dL, P<0.001), with 7 patients having a level <0.18 mg/dL. Thiamine levels were also lower in the extended group (median 211 vs. 438.5 nmol/L, P=0.0005). However, extended patients had higher levels of pyridoxine (23.2 vs. 11.1 ng/mL, P=0.03). Vitamin B12 and folate levels were not significantly different between the groups. There was significant variability in vitamin supplement prescription in both groups, and dietary data were not obtained. This study showed a high incidence of vitamin C deficiency in extended hours hemodialysis patients, suggesting that supplementation is warranted. It also supports an ongoing role for multivitamin supplementation in conventional hemodialysis patients.

Dietary intakes and biochemical status of B vitamins in a group of children receiving dialysis

OBJECTIVE

We investigated the dietary intake and biochemical status of B vitamins (thiamin, riboflavin, vitamin B6, and vitamin B12) in a group of mainly unsupplemented children with endstage renal disease receiving dialysis, to determine if B vitamin supplementation is indicated.

DESIGN

This was a cross-sectional, observational clinical trial.

SETTING

Children with endstage renal disease were receiving dialysis, under the care of Renal Services, at Starship Children's Health (Grafton, Auckland, New Zealand).

PATIENTS

We studied 12 children (including 7 girls, and 8 children receiving peritoneal dialysis) mean age 7.8 +/- 5.3 years (SD).

INTERVENTION

Three-day diet records were collected and analyzed with FoodWorks software. Blood was collected for vitamin assay testing.

MAIN OUTCOME MEASURE

Dietary intake of B vitamins was measured as a percentage of recommended dietary intake (RDI) or adequate intakes (AIs) for age. Biochemical status was measured as the concentration of each B vitamin compared with reference ranges.

RESULTS

Mean intakes from diet alone comprised <100% of the RDI or AI for each B vitamin. Mean intakes, with nutritional support, reached >100% of the RDI or AI for each B vitamin. All children achieved >100% RDI or AI for thiamin, riboflavin, and vitamin B12. Two children who were not receiving nutritional support received <100% of the RDI for vitamin B6. Blood levels of B vitamins were normal to high, compared with reference ranges, for each B vitamin in all children, indicating adequate status.

CONCLUSIONS

Intakes were adequate in the majority of children. Status was adequate in all children. In this group of children undergoing dialysis, B-vitamin supplementation was not indicated.

Trace elements and vitamins in maintenance dialysis patients

Although protein-energy malnutrition occurs commonly in patients with end-stage renal disease undergoing maintenance dialysis treatment, it is not the only form of malnutrition that may exist in these individuals. They may also suffer from deficiencies of micronutrients, particularly trace elements and vitamins. More commonly occurring vitamin deficiencies in maintenance dialysis patients include those for vitamin C (ascorbate), folate, vitamin B6 (pyridoxine), and 1,25-dihydroxycholecalciferol (calcitriol). Among trace elements, deficiencies may occur more commonly for iron, zinc, and possibly selenium, whereas toxicities are more common with aluminum and possibly copper. Evidence suggests that there is an abnormally high prevalence of antioxidant deficiency in maintenance dialysis patients, especially because a low intake of protein and energy may be associated with inadequate ingestion of antioxidant vitamins (ie, vitamins E and C and carotenoids). Thus, some micronutrient deficiencies in maintenance dialysis patients may contribute to the development of atherosclerotic cardiovascular disease. Dietary requirements for vitamins and trace elements in maintenance dialysis patients are reviewed and the recommended daily intakes are discussed.

Independent effects of residual renal function and dialysis adequacy on dietary micronutrient intakes in patients receiving continuous ambulatory peritoneal dialysis

BACKGROUND

Dialysis patients are at risk of vitamin and mineral deficiencies, not only because of losses during chronic hemodialysis or peritoneal dialysis but also because of low intakes.

OBJECTIVE

The objective was to determine the importance of urea clearance (calculated as K(t)/V) and residual renal function (RRF) in predicting micronutrient intakes in a large cohort of patients receiving continuous ambulatory peritoneal dialysis (CAPD).

DESIGN

We conducted a survey of dietary intakes in 242 CAPD patients and divided them into 3 groups according to their weekly urea clearance and RRF: WD group (n = 84), a urea clearance >/= 1.7 and a glomerular filtration rate (GFR) >/= 1 mL x min(-1) x 1.73 m(-2); DD group (n = 71), a urea clearance >/= 1.7 and a GFR < 1 mL x min(-1) x 1.73 m(-2); and ID group (n = 87), a urea clearance < 1.7.

RESULTS

Most of the patients had intakes of water-soluble vitamins and minerals that were lower than the recommended dietary allowance; most intakes were significantly higher in the WD group than in the DD and ID groups, except those of niacin and calcium. After age, sex, body weight, and the presence of diabetes were controlled for, total weekly urea clearance and the GFR (but not peritoneal dialysis urea clearance) were significantly associated with intakes of vitamins A and C, the B vitamins, and minerals (calcium, phosphate, iron, and zinc). Low intakes of vitamins and minerals with low RRF and urea clearance were the result of reduced overall food intakes, except for thiamine, vitamin B-6, and folic acid, which were deficient in the diet.

CONCLUSIONS

Supplementation with most water-soluble vitamins and minerals, including iron and zinc, should be considered in CAPD patients, especially those with low RRF and low urea clearance. The optimal dose needs to be determined.

Riboflavin is a determinant of total homocysteine plasma concentrations in end-stage renal disease patients

The effect of thiamine (vitamin B(1)) or riboflavin (vitamin B(2)) availability on fasting total homocysteine (tHcy) plasma levels in end-stage renal disease patients is unknown. A cross-sectional study was performed in a population of non-vitamin supplemented patients maintained on continuous ambulatory peritoneal dialysis. Red blood cell availability of thiamine (alpha-ETK) and of riboflavin (alpha-EGR), along with other predictors of tHcy plasma levels, was considered in the analysis. There was a linear association of alpha-EGR with tHcy plasma concentrations (P = 0.009), which was not observed for alpha-ETK. Among red blood cell vitamins, alpha-EGR was the only predictor of tHcy levels (P = 0.035), whereas alpha-ETK, red blood cell pyridoxal-5-phosphate supply (alpha-EGOT) and red blood cell folate levels had no effect. The risk for having a high tHcy plasma levels within the fourth quartile (plasma tHcy >38.3 micromol/L) was increased by an alpha-EGR > median (odds ratio, 4.706; 95% confidence interval, 1.124 to 19.704; P = 0.026). By way of contrast, alpha-ETK had no effect in these analyses. Independent predictors of tHcy plasma levels were serum albumin, alpha-EGR, red blood cell folate, and certain MTHFR genotypes. A logistic regression analysis showed that the MTHFR genotype is a predictor for having a tHcy plasma concentration within the fourth quartile. In summary, riboflavin availability, as measured by alpha-EGR, is a determinant of fasting tHcy plasma levels in peritoneal dialysis patients. This finding may have implications for tHcy lowering therapy in individuals with end-stage renal disease.

Vitamin B6 supplementation can improve peripheral polyneuropathy in patients with chronic renal failure on high-flux haemodialysis and human recombinant erythropoietin

BACKGROUND

High-flux haemodialysis (HD) has recently been vigorously promoted as a novel standard, and it can indeed efficiently reduce the occurrence of most uraemic symptoms due to middle molecular toxins and/or underdialysis. However, some symptoms remain problematical, particularly peripheral polyneuropathy (PPN). One of the possible reasons for this is that the patients may have low concentrations of some nutrients, e.g. vitamin B(6), necessary for normal peripheral neuron function.

METHODS

Predialysis serum pyridoxal-5'-phosphate (P5P) level was determined in 36 chronic HD patients who were undergoing high-flux HD and receiving human recombinant erythropoietin. Among them, 26 patients suffered from PPN. Prior to supplementation, these 26 patients were examined and their neurological symptoms were ranked according to our PPN symptom score. Vitamin B(6) (60 mg/day) was randomly prescribed to 14 of them, and vitamin B(12) (500 microg/day) was prescribed to the others. After 4 weeks, all the patients were re-examined.

RESULTS

We found that predialysis serum P5P levels of HD patients with PPN were not significantly lower than those of matched HD patients without PPN. Nonetheless, it was demonstrated that supplementation with vitamin B(6) for 4 weeks significantly increased the predialysis level of P5P and dramatically attenuated PPN symptoms compared with initial symptoms. No improvement was observed in response to vitamin B(12) supplementation.

CONCLUSION

This result suggests that although vitamin B(6) deficiency could not be demonstrated in patients with chronic renal failure on high-flux HD, vitamin B(6) supplementation was effective in improving PPN symptoms of various aetiologies, possibly because of vitamin B(6) resistance to PPN in these patients.

A tale of two homocysteines--and two hemodialysis units

Pharmacologic doses of folic acid are commonly used to reduce the hyperhomocysteinemia of end-stage renal disease (ESRD). Vitamin B12 acts at the same metabolic locus as folic acid, but information is lacking about the specific effects of high doses of this vitamin on homocysteine levels in renal failure. We therefore compared the plasma homocysteine concentrations of maintenance hemodialysis patients in two McGill University-affiliated urban tertiary-care medical centers that differed in the use of vitamin B12 and folic acid therapy. Patients in the first hemodialysis unit are routinely prescribed high-dose folic acid (HI-F, 6 mg/d), whereas those in the second unit receive high-dose vitamin B12 in the form of a monthly 1-mg intravenous injection, along with conventional oral folic acid (HI-B12, 1 mg/d). Predialysis homocysteine was 23.4 +/- 6.8 micromol/L (mean +/- SD) in the HI-F unit and 18.2 +/- 6.1 micromol/L in the HI-B12 unit (P < .002). Postdialysis homocysteine was 14.5 +/- 4.1 in the HI-F unit and 10.6 +/- 3.4 micromol/L in the HI-B12 unit (P = .0001). Multiple regression analysis indicated that high-dose parenteral vitamin B12 was associated with a lower homocysteine concentration even after controlling for the potential confounders of sex, serum urea, serum creatinine, urea reduction ratio, and plasma cysteine. Because this was a cross-sectional observational study, we cannot exclude the possibility that unidentified factors, rather than the different vitamin therapies, account for the different homocysteine levels in the two units. Careful prospective studies of the homocysteine-lowering effect of high-dose parenteral vitamin B12 in ESRD should be undertaken.

Relationship between methylmalonic acid and cobalamin in uremia

Relationship between methylmalonic acid and cobalamin in uremia.

BACKGROUND

To evaluate the requirement for routine supplementation with vitamin B12 and to study the effect of a change from injection to oral B12 supplementation, we examined the relationship between cobalamin and methylmalonic acid in plasma from 67 patients on chronic hemodialysis, all in regular therapy with intramuscular cobalamin injections (1 mg) every third month.

METHODS

Starting just before one cobalamin injection, blood samples were collected once a month during a nine-month withdrawal from regular cobalamin substitution to a final three-month period with cyanocobalamin tablets (1 mg) administered once daily.

RESULTS

Plasma cobalamin was above the lower reference limit in all subjects, and from a peak value one month after the regular injection, the cobalamin concentration during the withdrawal period decreased to a level below the point of origin, followed by a significant rise after cyanocobalamin tablets. The methylmalonic acid concentrations were above the reference interval. In the withdrawal period, the concentrations significantly increased further, followed by a significant decrease after oral cyanocobalamin substitution.

CONCLUSION

We demonstrated a within-patient inverse relationship between the concentrations of methylmalonic acid and cobalamin in plasma from these uremic patients. Despite the fact that only two of the patients developed subnormal plasma cobalamin values, we demonstrated a B12 depletion during the withdrawal period. Treatment with cyanocobalamin tablets once daily was found efficient, but the oral doses should possibly be increased.

Prevalence and determinants of hyperhomocysteinemia in hemodialysis and peritoneal dialysis

BACKGROUND

Hyperhomocysteinemia is an independent risk factor for atherosclerotic complications in patients with end-stage renal disease, although the mechanisms remain unclear. The major determinants of plasma homocysteine concentration are usually folate, vitamin B12, pyridoxal 5'-phosphate (vitamin B6), and glomerular filtration rate.

METHODS

We measured factors, including plasma folate, vitamin B12, vitamin B6, creatinine, as well as the dose and duration of dialysis, that might affect plasma homocysteine concentrations in 130 patients on hemodialysis (HD) and compared these observations with those in 46 patients on peritoneal dialysis (PD). Independent determinants of total homocysteine were identified using a multiple logistical regression analysis.

RESULTS

Total homocysteine values averaged 29.8 mumol/liter in HD patients, significantly higher than the mean value of 19.9 mumol/liter observed in patients on PD (P < 0.001). The prevalence of hyperhomocysteinemia was 90.8% among HD patients, significantly higher than the prevalence of 67.4% among PD patients. Folate values in HD patients averaged 45.5 nmol/liter and were significantly lower than in PD patients (104.2 nmol/liter, P < 0.001). For patients on HD, the only determinant of total homocysteine concentration was plasma folate (r = -0.31, P < 0.001). In contrast, for PD patients, total homocysteine did not correlate with plasma folate, vitamin B12, or vitamin B6.

CONCLUSIONS

Hyperhomocysteinemia is more prevalent and intense in HD patients compared with those on PD. The homocysteine response may become refractory to excess folate supplementation in PD patients.

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.

Detection of oxidants in uremic plasma by electron spin resonance spectroscopy

Depletion of antioxidants and the presence of products of free radical damage in plasma suggest that oxidative stress is increased in uremia. We have developed an application of electron spin resonance spectroscopy, and used this method to show that a stable oxidizing component or components of plasma accumulate in uremia. No oxidizing activity was detectable in plasma from subjects with normal renal function. The oxidant was detected by its capacity to oxidize the spin trap 3,5-dibromo-4-nitrosobenzene sulphonate (DBNBS). The oxidant was dialyzable from plasma, had an upper molecular weight limit of about 3,000 Daltons and was stable over many months. Physiological plasma concentrations of vitamin C, a water soluble congener of vitamin E and reduced glutathione were unable to inhibit the oxidizing capacity of uremic plasma. Thus, uremia is associated with accumulation of an endogenous oxidizing activity at much higher concentrations than in subjects with normal renal function.

Water soluble vitamins in chronic hemodialysis patients and need for supplementation

Forty-three patients on chronic hemodialysis who before the present study had only received a low-dose supplement of folic and ascorbic acid were studied prospectively for one year. After baseline values were obtained in month one, increasing doses of postdialysis vitamin supplements were prescribed for the vitamins which were found to be insufficient in order to determine the minimal amount of oral postdialysis supplement necessary to normalize vitamin levels. According to our results no systematic supplement was indicated for biotin, riboflavin or vitamin B12. For folic acid and vitamin C, supplementation with lower doses than those prescribed in many dialysis units allowed optimal vitamin levels in the majority of patients; 2 to 3 mg/week (300 to 400 micrograms/day) of folic acid and of 1000 to 1500 mg/week (150 to 200 mg/day) of vitamin C was considered sufficient. A severe pyridoxine deficiency was present in most (> 80%) unsupplemented patients, either as judged by pyridoxal-5-phosphate determinations in plasma or determination of specific enzyme activation in erythrocytes (EGOTo and alpha-EGOT); a postdialysis supplement of at least 100 to 150 mg/week of pyridoxine hydrochloride (> 15 to 20 mg/day) corrects this deficiency. The activity of the thiamine-dependent enzyme transketolase in erythrocytes (ETKo) was insufficient in 35% and marginal in 21% of the patients, while whole blood thiamine determined simultaneously in 10 of the ETKo-deficient patients was within the normal range. These results suggest that in uremia insufficient transketolase activity may be related to inhibition of the enzymatic system rather than to true vitamin deficiency. On a long-term basis a supplement of 200 to 300 mg/week of thiamine hydrochloride (30 to 45 mg/day) restored ETKo to satisfactory levels in most patients; whether this supplement is to be recommended warrants further studies.

Ascorbic acid supplements in patients receiving chronic peritoneal dialysis

Ascorbic acid supplements are commonly prescribed to patients with end-stage renal disease receiving peritoneal dialysis. To establish the need for ascorbic acid supplements, we evaluated seven chronic peritoneal dialysis patients during a supplement-free (phase I) period, and while receiving oral ascorbic acid (0.57 mmol/d [100 mg/d]) (phase II). Because of a proposed interaction with vitamin B6, patients were additionally supplemented with pyridoxine HCl (59.6 mumol/d [10 mg/d]) (phase III). Plasma levels and dialysate removal rates of total ascorbic acid and plasma pyridoxal-5-phosphate (PLP) were measured at the end of each phase. During phase I, plasma ascorbic acid levels (normal, 45 to 57 mumol/L [0.8 to 1.0 mg/dL]) declined slightly from 74 +/- 11 mumol/L (1.3 +/- 0.2 mg/dL) to 62 +/- 11 mumol/L (1.1 +/- 0.2 mg/dL) (P less than 0.02) at the end of the third week, and then remained stable to the end of the fourth week. Plasma ascorbic acid levels were no different in patients with or without residual renal function. With the addition of vitamin C supplements, plasma ascorbic acid levels increased by 45% of the baseline value at the end of phases II (P less than 0.001). The dialysate removal rate of ascorbic acid was 0.28 +/- 0.03 mmol/d (50 +/- 6 mg/d) at the end of phase I, and increased by 57% of the baseline value at the end of phases II (P less than 0.001). However, the peritoneal clearance of ascorbic acid remained unchanged during all phases the study. Pyridoxine depletion or repletion had no effect on plasma ascorbic acid levels (P greater than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Correction of subclinical ascorbate deficiency in patients receiving dialysis: effects on plasma oxalate, serum cholesterol, and capillary fragility

Whole blood ascorbate, plasma oxalate, serum cholesterol, and capillary fragility were measured at monthly intervals for 3 mth in 7 patients receiving continuous ambulatory peritoneal dialysis and 4 receiving haemodialysis, to whom ascorbate supplements had not been prescribed for at least 12 mth. Ascorbate supplements, 25 mg/day, were prescribed for the first month and 50 mg/day for the second month; in the final month patients received no supplements. Whole blood ascorbate was below normal in 6/11 patients at the start of the study but was normal in 10/11 patients when taking ascorbate 50 mg/day. No significant changes in plasma oxalate were observed with these doses of ascorbate, and correction of ascorbate deficiency had no effect on serum cholesterol, mean cell volume, or the results of capillary fragility tests. In a supplementary study, ascorbic acid 500 mg/day was administered for 3 wk to 11 patients. This resulted in a significant rise in mean plasma oxalate from 30.3 (SEM 3.5) to 48.4 (SEM 20.3) mumol/l.