Folate and zinc status of chronic hemodialysis patients

Folate supplementation at a level of 15 to 35 mg per week is routinely prescribed for many chronic hemodialysis patients in B.C. In recent studies involving these levels of folate supplementation, RBC folate concentrations ranged from near the upper limit of normal to 1.5 times this upper limit. Initially there was research suggesting that high dose folate supplementation impaired zinc absorption but more recent studies refute this hypothesis. A beneficial effect of high dose folate supplementation is lowering of plasma homocysteine levels. This may be desirable since the homocysteinemia observed in chronic renal failure patients may be a factor in their commonly occurring premature vascular disease. The present study addressed folate needs on a nutritional basis but did not investigate folate's effect on homocysteine levels. The study involved chronic hemodialysis patients and was designed to: 1. assess whether patients consuming the Recommended Nutrient Intake for folate, require a folate supplement to maintain normal folate stores; 2. assess whether patients receiving a supplement of 5 mg of folate per day will have RBC folate levels exceeding the upper limit of the normal range; 3. compare serum zinc concentrations (and in some cases hair zinc levels as well) of patients receiving no zinc supplement or a 22.5 mg per day zinc supplement, to each other and to normal values; 4. assess whether a supplement of 5 mg of folate per day is associated with impaired zinc status; 5. in the event that a 5 mg per day folate supplement is associated with impaired zinc status, assess whether a supplement of 22.5 mg of zinc per day is associated with an improvement in zinc status; and 6. determine average daily energy, protein, folate and zinc intakes of patients. A 2x2 factorial quasiexperimental design was employed. The study included 21 clinically stable chronic hemodialysis patients between the ages of 25 and 69, who were receiving folate and/or zinc supplements at certain specific levels. Subjects were entered into treatment groups based on the following folate/zinc supplementation levels: no folate, no zinc; no folate, 22.5 mg zinc/day; 5 mg folate/day, no zinc; 5 mg folate/day, 22.5 mg zinc/day. Folate status was assessed using RBC folate concentration. Serum zinc concentration was measured in all subjects. Hair zinc level was determined in 6 of the zinc-supplemented subjects. A food frequency questionnaire was developed to determine dietary folate and zinc intakes. Subjects kept 3 day food records so average daily energy and protein intakes could be determined. Study results indicated no significant difference in protein intake (g/kg b.w.) or energy intake (expressed as a percent of requirement) among the four treatment groups. Differences in dietary folate intakes among the four treatment groups as well as between zinc-supplemented and non zinc-supplemented subjects, were not significant (p≤0.05). Mean dietary folate intake for all study subjects was 4.2 ug/kg b.w. RBC folate concentration was normal in both treatment groups receiving no supplemental folate. In contrast, the RBC folate concentration for both folate-supplemented groups was approximately 6.5 to 7 times the upper limit of the normal range. The difference between RBC folate concentration for folate supplemented and unsupplemented groups was highly significant (p