Randomized Trial of Folic Acid for Prevention of Cardiovascular Events in End-Stage Renal Disease : Journal of the American Society of Nephrology

Journal Logo

Epidemiology and Outcomes

Randomized Trial of Folic Acid for Prevention of Cardiovascular Events in End-Stage Renal Disease

Wrone, Elizabeth M.*,†; Hornberger, John M.; Zehnder, James L.§; McCann, Linda M.*; Coplon, Norman S.*; Fortmann, Stephen P.

Author Information
Journal of the American Society of Nephrology 15(2):p 420-426, February 2004. | DOI: 10.1097/01.ASN.0000110181.64655.6C
  • Free


End-stage renal disease (ESRD) afflicts nearly half a million people in the United States (1) and carries mortality rates from cardiovascular disease that are 10-fold to 100-fold higher than those of the general population (2). In ESRD, mean total homocysteine levels (tHcy) are commonly elevated, and the role of homocysteine as risk factor has been suggested in some small prospective studies (3–5). However, some studies in ESRD have observed an inverse relationship between tHcy and cardiovascular disease (6,7). Homozygosity for the common C677T mutation of methylenetetrahydrofolate reductase (MTHFR) (8), a key enzyme in homocysteine metabolism may also be associated with elevated tHcy levels and cardiovascular disease in ESRD (7,9).

Total serum homocysteine (tHcy) is readily reduced with folic acid and vitamin B12 in the general population. In ESRD, higher doses of folic acid appear to be required, and normal levels of homocysteine are not commonly achieved (10). Patients with ESRD are frequently given multivitamin supplements to compensate for dialysate losses and dietary restrictions; however, the optimal amount of folic acid supple- mentation in ESRD for reduction of tHcy has not been established.

To explore the relationship between folic acid, homocysteine, and clinical outcomes, we present the results of a randomized trial of folic acid for prevention of cardiovascular morbidity/mortality in patients with ESRD. The primary question addressed is “does supplementation with a multivitamin containing folic acid in 5-mg or 15-mg doses reduce a composite end point of mortality and cardiovascular events over 3 yr compared with standard therapy (1 mg of folic acid)?” Secondarily, “do these higher doses of folic acid prevent vascular access clotting?” In addition, we test the hypothesis that high levels of baseline tHcy and the TT genotype of the C677T mutation of MTHFR are associated with an increased incidence of cardiovascular events and mortality.

Materials and Methods


This randomized, double blind, three-arm study of homocysteine reduction was performed at 10 affiliated nonprofit outpatient dialysis facilities in Northern California. At the time of enrollment, approximately 1100 patients received treatment at these outpatient facilities. Patients were recruited by study dietitians at their dialysis units. Written consent was obtained from every patient after a full explanation of the study, which was approved by the Administrative Panel on Human Subjects in Medical Research of Stanford University. Adult patients undergoing hemodialysis or peritoneal dialysis and who were able to participate in the consent process were eligible for the study. Patients who were undergoing intradialytic parenteral nutrition, anticipating a living-related kidney transplant, receiving an anti-seizure medication, residing in an institution, or were terminally ill were excluded from the study.


Participants were randomly assigned by computer to one of three treatment groups using a biased-coin program. Treatment consisted of identically appearing capsules containing either (1) standard therapy with renal multivitamin containing 1 mg of folic acid; (2) renal multivitamin containing 5 mg of folic acid; or (3) renal multivitamin containing 15 mg of folic acid. All capsules contained: 12.5 mg of pyridoxine, 6 μg of cobalamin, 60 mg of ascorbic acid, 1.5 mg of thiamine, 20 mg of niacinamide, 10 mg of pantothenic acid, and 0.3 mg of biotin. Participants were instructed to replace their regular renal multivitamin with the study capsule once daily. Those who were not taking a multivitamin before the study were asked to begin study multivitamin. R&D Laboratories, Inc. (Marina del Rey, CA) donated study capsules and participated in determining the formula of the multivitamins. This donor did not contribute to study design, data collection, analysis, interpretation of the data, or the decision to approve the manuscript.

Randomization was stratified on age (18 to 54, 55 to 69, or >70 yr), gender, diabetes, and tHcy > 37 μmol/L. To maintain double-blind status, neither the person performing the randomization nor the person preparing study medication for distribution to clinical coordinators had direct contact with participants. Patients, clinicians, and study staff with patient contact did not have access to any information that could identify treatment arm. Randomization codes were kept in a separate, locked file.


Baseline clinical variables were collected at the time of enrollment. These included age, gender, race/ethnicity, diabetes status, smoking history, duration of renal replacement therapy, prescribed medication use including dose and formulation of all vitamin supplements, height, and dry weight (the prescribed, post-dialysis weight). For those on hemodialysis, the following were collected: vascular access history, pre and dialysis systolic and diastolic BP (averaged over nine treatments), and recent dialysis adequacy parameters collected using the K/DOQI-recommended slow flow, stop-pump procedure (11). Adequacy parameters included normalized protein catabolic rate and Kt/V (single-pool, variable volume), a unitless measure of dialysis dose. Cardiovascular disease was defined as a history of coronary artery intervention, myocardial infarction, stroke, transient ischemic attack, carotid endarterectomy, or other clinical evidence of cardiovascular disease as documented in hospital discharge summaries or history and physical examination at admission to the dialysis unit. At baseline, patients from four facilities were further assessed for compliance with previous prescribed vitamins and for over-the-counter vitamin supplement intake. THcy, folate, and vitamin B12 levels were assessed at baseline, and tHcy and folate levels at 2 mo, 6 mo, and 18 mo. All patients had study blood samples drawn in conjunction with routine monthly specimens, pre-dialysis for those on hemodialysis. THcy concentrations were determined by HPLC of serum specimens by Quest Diagnostics (normal range, 2.8 to 13.5 μmol/L). Serum folate was determined using an ion capture assay, which remains linear up to 45.3 nmol/L (normal range, 7.0 to 28.1 nmol/L). Specimens with levels higher than 45.3 nmol/L were diluted. Vitamin B12 determination was performed using standard clinical diagnostic techniques by Quest Diagnostics (normal range, 148–812 pmol/L). Total cholesterol, albumin, blood urea nitrogen, creatinine, and pre-albumin determinations were performed at Satellite Laboratory Services, Inc. as part of the routine monthly care. Identification of the C677T translocation was performed for the first 459 enrolled using HinfI digestion and PCR amplification from specimens of peripheral blood lymphocytes as described by Frosst et al. (8). PCR analysis was performed in the Molecular Diagnosis Laboratory, Department of Pathology, Stanford University Medical Center.


Main outcomes of interest were cardiovascular events and mortality. Principal diagnoses and hospital discharge summaries were reviewed for ascertainment of coronary artery intervention, myocardial infarction, stroke, transient ischemic attack, carotid endarterectomy, limb amputation, or death. Secondary outcome was vascular access thrombosis (among those with arteriovenous fistulae). Dialysis records and discharge summaries were reviewed for ascertainment of vascular access events. Additional information regarding renal transplantation, relocation out of a participating facility, or transfer to institutional care was collected.

Statistical Analyses

We determined that we needed a sample size of 175 per treatment arm to detect a 20% difference in the composite endpoint after 3 yr with a power of 70% and an alpha of 0.05. With this sample size, we estimated that we had 90% power with an alpha of 0.05 to detect a 10% difference in tHcy levels between two groups.

To compare the baseline characteristics, we used the two-sample t test and the χ2 test for analysis of continuous and categorical variables, respectively. The non-parametric Jonckheere test was used to evaluate whether there was a consistent reduction in the tHcy across the three treatment groups (12). THcy reduction at follow-up time points was incorporated into the model as a natural logarithmic transformation of the log ratios of follow-up to baseline tHcy due to right-skewed distributions.

We used Kaplan-Meier survival estimates to analyze time to first event by treatment arm. All analyses were performed on an intention-to-treat basis. Additional estimates were analyzed for quartile of baseline tHcy and C677T genotype. Because we found that the hazard was not proportional over time, parametric survival models were developed for the primary and secondary endpoints to assess the effects of the following covariates: treatment arm, age, gender, diabetes status, baseline tHcy, C677T genotype, smoking status, albumin, baseline vitamin usage, body mass index, race/ethnicity, BP, dialysis modality, and serum total cholesterol. Results are reported as mean ± SD, except where otherwise indicated. Data analyses were performed using SAS Systems version 6.1.2 (SAS Institute, Inc., Cary, North Carolina).


Patient Characteristics

From March 1998 to May 1999, 578 patients with ESRD were enrolled in the protocol. Of these, 510 patients (468 on hemodialysis; 42 on peritoneal dialysis) were randomized, received study intervention, and included in analyses (intention to treat) (Figure 1). Baseline demographic and clinical characteristics by treatment arm of the 510 randomized patients who received study intervention are shown in Table 1. There was no difference in any of the demographic, clinical, and laboratory values among the treatment groups with the exception of Kt/V, (P = 0.04). The racial/ethnic groups represented were 207 non-Hispanic white, 153 Hispanic, 76 Asian/Pacific Islander, 58 African-American, and 18 other or multiple. Etiology of ESRD was: 26 diabetes type I, 179 diabetes type II, 125 hypertension/large vessel disease/cardiac, 109 glomerulonephritis, and 71 other.

Figure 1.:
Trial flow diagram.
Table 1:
Baseline characteristics of study population by folic acid group

Median duration of treatment was 24 mo. Patients terminated study interventions for the following reasons: death (n = 189), received kidney transplant (n = 58), moved away (n = 37), and return of renal function (n = 2). There was no differential dropout among the treatment arms (Figure 1). Eight patients discontinued study medication due to side effects, which included nausea, abdominal discomfort, “hunger and weight gain.” The side effects were equally distributed among the treatment arms (P = 0.88).

Survival and Cardiovascular Events

As depicted on the Kaplan-Meier curve (Figure 2), there was no difference in the composite end point at 24 mo (43.7% in arm 1, 38.6% in arm 2, 47.1% in arm 3; log-rank P = 0.47) among the treatment arms. See Table 2 for numbers of individual events by treatment arm. Similarly, there was no difference among the treatment arms in total survival or cardiovascular events when analyzed separately.

Figure 2.:
Event-free survival by folic acid group.
Table 2:
Number of events at 24 mo by folic acid group and baseline total homocysteine quartile (low to high)

Vascular Access Clotting

Analyzing time to first vascular access clot for the hemodialysis patients, the Kaplan-Meier curve revealed no difference in event rates at 24 mo among the treatment arms (36.9% arm 1, 31.1% arm 2, 38.1% arm 3; log-rank P = 0.82)

Baseline tHcy and C677T Mutation of MTHFR

Using the primary outcome of cardiovascular events and mortality, there was a significant difference in event rates among quartiles of baseline tHcy (from lowest to highest at 24 mo: 54.5% quartile 1, 41.8% quartile 2, 41.2% quartile 3, 34.7% quartile 4; log-rank P = 0.033) (Figure 3). This relationship was similar when total survival and cardiovascular events were analyzed separately. See Table 2 for numbers of individual events at 24 mo by quartile baseline tHcy. There was no difference in event rates among the MTHFR genotypes (log-rank P = 0.60).

Figure 3.:
Event-free survival by quartile of baseline total homocysteine (quartile 1 lowest).

Response to Treatment

Adherence was assessed by serum folate levels. Patients in arm 1 (1 mg of folic acid) whose serum folate level dropped during follow-up were considered non-adherent. Patients in arms 2 (5 mg of folic acid) or 3 (15 mg of folic acid) were considered non-adherent if follow-up folate was not elevated by at least 45.3 nmol/L over baseline. Non-adherence rates were similar among all three arms at all three follow-up assessments (percentage non-adherent by treatment arms 1 through 3, respectively: 21, 18, 17 [P = 0.69] at 2 mo; 25, 26, 21 [P = 0.69] at 6 mo; and 23, 18, 33 [P = 0.17] at 18 mo).

All three treatments reduced tHcy at 2 mo, 6 mo, and 18 mo when compared with baseline tHcy in an intention-to-treat analysis. Among those remaining in the study at 18 mo, the difference in geometric mean tHcy levels from baseline to 18 mo was 3.7 μmol/L for arm 1 (1 mg of folic acid), 4.3 μmol/L for arm 2 (5 mg of folic acid), and 10.2 μmol/L for arm 3 (15 mg of folic acid). The differences between each arm were significant by Jonckheere test (P = 0.049 at 18 mo). At 18 mo, there was no difference in the percentage of patients with tHcy <15 μmol/L (7.69% arm 1, 6.85% arm 2, and 10.0% arm 3; P = 0.81).

Multivariate Analyses

In a parametric survival model predicting the primary outcome, mortality, and cardiovascular events, with baseline tHcy and treatment arm as predictors, only baseline tHcy remained significant. For every 1-μmol/L increase in tHcy, the RR for an event decreased by 1.4% (P = 0.0015). Treatment arm variables were NS. Models were developed with the following predictor variables: treatment arm, age, gender, diabetes status, baseline tHcy, C677T genotype, smoking status, albumin, baseline vitamin usage, body mass index, race/ethnicity, BP, dialysis modality, and serum total cholesterol. Age, albumin, and race/ethnicity remained the only significant predictors.


Whereas mean albumin was lower among those with low tHcy (Table 2), there was no evidence for reversal of effects of high tHcy among those with low serum albumin on events at 24 mo (Figure 4). No interactions were detected for baseline tHcy quartile with treatment arm, MTHFR genotype, or albumin quartile.

Figure 4.:
Composite events at 24 mo by high and low (split at median) tHcy and albumin.


The findings of this randomized, double blind clinical trial of folic acid therapy in ESRD fail to support any effect of doses above 1 mg/d on cardiovascular disease or other outcomes. The trial design provided adequate but limited power; however, there is little evidence of any benefit trend that might become significant in a larger trial. Baseline characteristics and compliance were well balanced across groups. Compliance did fall over time, so the intention-to-treat analysis would underestimate a true effect; however, the highest incidence of the composite end point was in the 15-mg group, so this seems an unlikely explanation for the null result. The effect of folic acid on homocysteine was less than we anticipated from preliminary data, and we cannot exclude the possibility that higher doses of folic acid would be beneficial. We conclude that folic acid supplementation in ESRD is unlikely to produce benefit at doses between 1 and 15 mg/d. Further elucidation of the role of tHcy and other risk factors in the pathogenesis of cardiovascular disease is needed before establishing guidelines concerning higher doses of folic acid in ESRD.

Unexpectedly, higher tHcy at the time of study enrollment was associated with better clinical outcomes. This finding is contrary to many prospective studies of the general population, but it is similar to findings for other cardiovascular risk factors in patients with ESRD, probably due to confounding. Although we were able to achieve a modest reduction in tHcy with the higher doses of folic acid, this reduction did not positively or negatively effect outcomes, nor did it achieve a statistically significant improvement in the fraction of patients who reached normal tHcy levels. These dose-response characteristics are in concordance with those of other studies (13–15). Homozygosity for C677T MTHFR genotype was not associated with higher clinical event rates in this prospective analysis.

The inverse association between baseline tHcy and clinical outcomes may have several explanations. First, determination of tHcy in ESRD may not represent lifetime tHcy exposure, as other factors related to renal replacement therapy, such as dialysis dose, may influence tHcy levels. Second, there may be unmeasured nutritional and/or inflammatory factors that serve to suppress tHcy levels while simultaneously augmenting atherosclerosis (16,17). Third, these results may demonstrate “reverse epidemiology.” Reverse epidemiology has been described for other cardiovascular risk factors where a dramatically different relationship occurs for outcomes in patients with ESRD compared with the general population (6,22–24). Underlying factors are responsible for driving the apparent reversal of relationships seen in statistical analyses, rather than a reversal of basic pathophysiology. This has been demonstrated in ESRD in a hypothetical model where adjustment for malnutrition reverses the relationship between cholesterol and survival (18).

Fourth, the homocysteine hypothesis of atherosclerosis has yet to be fully confirmed. Despite two recent positive clinical trials of folic acid in those with normal renal function (19,20) not all epidemiologic studies in the general population have supported a causal relationship (21–24). Further clouding our understanding of the pathophysiology is evidence that folate may have direct beneficial effects on the vasculature, independent of homocysteine (25,26). Our study might not have been able to detect this folate effect because of the absence of a placebo arm or the much higher levels of folate and tHcy prevalent in ESRD or both.

In our study, higher doses of folic acid reduced tHcy modestly. This is not surprising given that patients with ESRD on chronic dialysis appear to be resistant to the tHcy-reducing effects of higher doses of folic acid. We found an inverse relationship between tHcy and cardiovascular events and mortality; therefore, the lack of difference in outcomes between the groups could have resulted from three hypothetical situations. One, tHcy reduction is beneficial, and this study was underpowered due to small effect size and due to strong confounding of associations. Two, tHcy reduction is harmful, and this study was too small to detect differences in outcomes. Three, tHcy is not a causative agent (or plays a very minor role) in this group of patients who tend to suffer from multiple, advanced chronic diseases. The answer will likely be discovered in populations where tHcy reduction is more readily achieved, such as in renal transplant recipients or chronic kidney disease, where clinical trials are already underway.

Our study likely represents the largest and longest prospective study of cardiovascular events, tHcy, and the MTHFR genotype in ESRD to date. Our prospective findings are similar to those of Suliman et al. (6) and differ in direction from those of Moustapha et al. (4). The most notable contrast to our findings originates from the CREED (5) study, where tHcy was found to be an independent predictor of fatal and nonfatal atherothrombotic events. Fundamental design differences in CREED, such as exclusion of those with preexisting cardiovascular disease or on folic acid supplementation, make direct comparisons difficult. The lack of association between C677T genotype of MTHFR and outcomes is consistent with findings of a meta-analysis (21) and a study in Japanese hemodialysis patients (27).

There are several limitations of this study. First, it was an effectiveness study, performed in a clinical environment. There were no washout or run-in periods to establish patterns of compliance or to examine the effect of the study medication after creating a uniform, supplement-free environment. Previous supplement use, however, did not influence homocysteine reduction in this study. Conceivably, with a vitamin-free run-in period, there would have been patients with higher baseline tHcy and correspondingly larger reductions in response to treatment. Despite the fact that more than three quarters of the participants were taking a folate-containing multivitamin before enrollment, there was a dose response at 2 and 18 mo. The fortification of the national grain supply started during this study in 1998 and added 0.1 mg/d folic acid to the typical diet, an amount that we would not anticipate to influence a study using 1 to 15 mg/d folic acid. All three treatment arms achieved a significant reduction in tHcy. We could have conceivably missed an effect of folic acid if there was one between a placebo and 1 mg. Finally, survivor bias can exert a strong influence when patients are enrolled with varying degrees of dialysis duration. Ideally, clinical studies include patients from the same duration cohort and attempt to control for differences in residual renal function.

In conclusion, for patients with ESRD treated with dialysis, these results do not support administration of doses of folic acid beyond the generally recommended 1 mg/d. There are several large clinical trials in the general population that over the next few years will shed light on the role of folic acid and other B-vitamins in preventing cardiovascular disease, as well as a large trial in ESRD and renal insufficiency patients that is using higher doses of folic acid.

Dr. Wrone was supported by a National Institutes of Health Training Grant DK 07357–16A to the Division of Nephrology, Department of Medicine, Stanford University School of Medicine from July 1997 through June 1999. Study multivitamins were provided by R&D Laboratories, Inc., Marina del Rey, CA.

1. U. S. Renal Data System, USRDS 2001 Annual Data Report: Atlas of End-Stage Renal Disease in the United States. Bethesda, MD, National Institutes of Health, National Institute of Diabetes and Digestive and Kidney Diseases, 2001
2. Foley RN, Parfrey PS, Sarnak MJ: Clinical epidemiology of cardiovascular disease in chronic renal disease. Am J Kidney Dis 32: S112–S119, 1998
3. Bostom AG, Shemin D, Verhoef P, Nadeau MR, Jacques PF, Selhub J, Dworkin L, Rosenberg IH: Elevated fasting total plasma homocysteine levels and cardiovascular disease outcomes in maintenance dialysis patients. A prospective study. Arterioscler Thromb Vasc Biol 17: 2554–2558, 1997
4. Moustapha A, Naso A, Nahlawi M, Gupta A, Arheart KL, Jacobsen DW, Robinson K, Dennis VW: Prospective study of hyperhomocysteinemia as an adverse cardiovascular risk factor in end-stage renal disease. Circulation 97: 138–141, 1998
5. Mallamaci F, Zoccali C, Tripepi G, Fermo I, Benedetto FA, Cataliotti A, Bellanuova I, Malatino LS, Soldarini A: Hyperhomocysteinemia predicts cardiovascular outcomes in hemodialysis patients. Kidney Int 61: 609–614, 2002
6. Suliman ME, Qureshi AR, Barany P, Stenvinkel P, Filho JC, Anderstam B, Heimburger O, Lindholm B, Bergstrom J: Hyperhomocysteinemia, nutritional status, and cardiovascular disease in hemodialysis patients. Kidney Int 57: 1727–1735, 2000
7. Wrone EM, Zehnder JL, Hornberger JM, McCann LM, Coplon NS, Fortmann SP: An MTHFR variant, homocysteine, and cardiovascular comorbidity in renal disease. Kidney Int 60: 1106–1113, 2001
8. Frosst P, Blom HJ, Milos R, Goyette P, Sheppard CA, Matthews RG, Boers GJ, den Heijer M, Kluijtmans LA, van den Heuvel LP, et al.: A candidate genetic risk factor for vascular disease: a common mutation in methylenetetrahydrofolate reductase. Nat Genet 10: 111–113, 1995
9. Vychytil A, Fodinger M, Wolfl G, Enzenberger B, Auinger M, Prischl F, Buxbaum M, Wiesholzer M, Mannhalter C, Horl WH, Sunder-Plassmann G: Major determinants of hyperhomocysteinemia in peritoneal dialysis patients. Kidney Int 53: 1775–1782, 1998
    10. Bostom AG, Culleton BF: Hyperhomocysteinemia in chronic renal disease. J Am Soc Nephrol 10: 891–900, 1999
    11. I. NKF-K/DOQI clinical practice guidelines for hemodialysis adequacy: update 2000. Am J Kidney Dis 37: S7–S64, 2001
    12. Hollander M, Wolfe, D: Nonparametric Statistical Methods. New York, John Wiley and Sons, Inc., 1973
    13. Bostom AG, Shemin D, Lapane KL, Hume AL, Yoburn D, Nadeau MR, Bendich A, Selhub J, Rosenberg IH: High dose-B-vitamin treatment of hyperhomocysteinemia in dialysis patients. Kidney Int 49: 147–152, 1996
    14. Bostom AG, Shemin D, Gohh RY, Beaulieu AJ, Jacques PF, Dworkin L, Selhub J: Treatment of mild hyperhomocysteinemia in renal transplant recipients versus hemodialysis patients. Transplantation 69: 2128–2131, 2000
      15. Bostom AG, Shemin D, Gohh RY, Beaulieu AJ, Bagley P, Massy ZA, Jacques PF, Dworkin L, Selhub J: Treatment of hyperhomocysteinemia in hemodialysis patients and renal transplant recipients. Kidney Int 59 [Suppl 78]: S246–S252, 2001
        16. Brulez HF, van Guldener C, Donker AJ, ter Wee PM: The impact of an amino acid-based peritoneal dialysis fluid on plasma total homocysteine levels, lipid profile and body fat mass. Nephrol Dial Transplant 14: 154–159, 1999
        17. Bergstrom J, Lindholm B: Malnutrition, cardiac disease, and mortality: an integrated point of view [editorial] [In Process Citation]. Am J Kidney Dis 32: 834–841, 1998
          18. Coresh J, Longenecker JC, Miller III ER, Young JH, Klag MJ: Epidemiology of cardiovascular risk factors in chronic renal disease. J Am Soc Nephrol 9: S24–S30, 1998
          19. Schnyder G, Roffi M, Pin R, Flammer Y, Lange H, Eberli FR, Meier B, Turi ZG, Hess OM: Decreased rate of coronary restenosis after lowering of plasma homocysteine levels. N Engl J Med 345: 1593–1600, 2001
          20. van Dijk RA, Rauwerda JA, Steyn M, Twisk JW, Stehouwer CD: Long-term homocysteine-lowering treatment with folic acid plus pyridoxine is associated with decreased blood pressure but not with improved brachial artery endothelium-dependent vasodilation or carotid artery stiffness: A 2-year, randomized, placebo-controlled trial. Arterioscler Thromb Vasc Biol 21: 2072–2079, 2001
            21. Brattstrom L, Wilcken DE, Ohrvik J, Brudin L: Common methylenetetrahydrofolate reductase gene mutation leads to hyperhomocysteinemia but not to vascular disease: The result of a meta- analysis. Circulation 98: 2520–2526, 1998
            22. Folsom AR, Nieto FJ, McGovern PG, Tsai MY, Malinow MR, Eckfeldt JH, Hess DL, Davis CE: Prospective study of coronary heart disease incidence in relation to fasting total homocysteine, related genetic polymorphisms, and B vitamins: the Atherosclerosis Risk in Communities (ARIC) study. Circulation 98: 204–210, 1998
              23. Alfthan G, Pekkanen J, Jauhiainen M, Pitkaniemi J, Karvonen M, Tuomilehto J, Salonen JT, Ehnholm C: Relation of serum homocysteine and lipoprotein(a) concentrations to atherosclerotic disease in a prospective Finnish population based study. Atherosclerosis 106: 9–19, 1994
                24. Verhoef P, Hennekens CH, Allen RH, Stabler SP, Willett WC, Stampfer MJ: Plasma total homocysteine and risk of angina pectoris with subsequent coronary artery bypass surgery. Am J Cardiol 79: 799–801, 1997
                  25. Doshi SN, McDowell IF, Moat SJ, Payne N, Durrant HJ, Lewis MJ, Goodfellow J: Folic acid improves endothelial function in coronary artery disease via mechanisms largely independent of homocysteine lowering. Circulation 105: 22–26, 2002
                  26. Doshi SN, McDowell IF, Moat SJ, Lang D, Newcombe RG, Kredan MB, Lewis MJ, Goodfellow J: Folate improves endothelial function in coronary artery disease: An effect mediated by reduction of intracellular superoxide? Arterioscler Thromb Vasc Biol 21: 1196–1202, 2001
                    27. Kimura H, Gejyo F, Suzuki S, Miyazaki R: The C677T methylenetetrahydrofolate reductase gene mutation in hemodialysis patients. J Am Soc Nephrol 11: 885–893, 2000
                    Copyright © 2004 The Authors. Published by Wolters Kluwer Health, Inc. All rights reserved.