Elevated serum homocysteine as a predictor for vitamin B12 or folate deficiency

Abstract: Tissue deficiency of vitamin B₁₂ and folate results in an increase in serum homocysteine (sHcy). We have measured sHcy in patients with reduced serum vitamin B₁₂ and/or red cell folate (RCF) to determine its usefulness as a discriminant for the diagnostic interpretation of reduced vitamin levels. Of 3846 patients who had serum vitamin B₁₂ and RCF assayed, 335 (9%) had reduced vitamin levels. Multivariate analysis showed a significant association between sHcy and serum creatinine (p = 0.0001), positive intrinsic factor (IF) antibody or neutrophil hypersegmentation (NHS) (p = 0.001), increased MCV (p = 0.014) and low RCF (p = 0.025) but no relationship with the level of serum vitamin B₁₂ or haemoglobin. After censoring the patients with renal impairment (n = 54), the distribution of the remaining 72 patients with elevated sHcy was 37/151 (25%) with low serum vitamin B₁₂ with or without low RCF and 35/130 (27%) with low RCF alone. sHcy correctly identified response to vitamin therapy in 33/35 (94%) patients who had adequate parameters to assess response. The positive predictive values of IF antibody/NHS, macrocytosis and/or low RCF for elevated sHcy were 100% and 34% respectively. Twenty-four percent of patients with a low serum vitamin B₁₂ and elevated sHcy had no abnormal haematologic parameters as determined by the routine laboratory staff. These data suggest that the usefulness of measuring sHcy in a routine diagnostic setting is limited and a careful review of the peripheral blood for macrocytosis and NHS plus determination of RCF may be a more cost-effective process than sHcy assay in most instances to determine the presence of tissue deficiency.     

Serum homocysteine in routine evaluation of potential vitamin B12 and folate deficiency

Total serum homocysteine (Hcy) was measured in patients with either low serum folate, low serum vitamin B12 (B12), or potential metabolic defects, in order to evaluate Hcy as an indicator of the tissue status of the two vitamins. An increased Hcy supported the diagnosis of frank tissue deficiency in those patients in whom tissue deficiency was evident by other means. A Hcy within the reference interval enabled the clinician to identify those patients whose low serum vitamin level and symptoms did not reflect a tissue deficiency of B12 or folate of clinical consequence. Children with inherited disturbances of B12 metabolism, and whose serum B12 was within the reference interval, were correctly identified by an increased Hcy. A declining Hcy was evidence of correction of a deficiency even when other laboratory or clinical measurements of a response were obscured.     

A randomized,double-blind,placebo-controlled study of oral vitamin B12 supplementation in older patients with subnormal or borderline serum vitamin B12 concentrations

OBJECTIVES: To determine the effect of small doses of oral cyanocobalamin supplements in older patients with low or borderline serum vitamin B12 concentrations but no other evidence of pernicious anemia (PA). DESIGN: Randomized, double-blind, placebo-controlled study assessing the efficacy of oral cyanocobalamin 10 microg and 50 microg daily for 1 month. SETTING: Two geriatric hospitals in the North Western Health Care Network, Melbourne, Australia. PARTICIPANTS: Thirty-one inpatients with serum vitamin B12 levels between 100 and 150 pmol/L, without PA, other malabsorption disorders, or progressive neurological or terminal illness. The mean age was 81.4 years. INTERVENTION: After informed consent, a medical and drug history was taken and the Mini-Mental State Examination (MMSE) completed. A dietitian made assessment of oral cobalamin intake. Blood was taken for serum vitamin B12, serum and red cell folate assay, full blood examination, fasting serum gastrin, parietal and intrinsic factor antibodies, fasting serum homocysteine, and creatinine. Patients were then randomized to receive 10 microg oral cyanocobalamin, 50 microg oral cyanocobalamin, or placebo treatment for 1 month, after which the investigations and clinical examinations were repeated. MEASUREMENTS: Percentage change in the level of vitamin B12, homocysteine, folate, and red cell parameters and absolute changes in MMSE were calculated and compared between groups. The groups were compared on the number of responders who improved their level of B12 by 20%. Chi-square calculations on changes in serum vitamin B12 concentration were also performed. RESULTS: Mean serum vitamin B12 +/- standard deviation improved by 51.7 +/- 47.1% in the 50-microg group, 40.2 +/- 34.4% in the 10-microg group, and 11.7 +/- 24.5% in the placebo group. The change in the 50-microg cyanocobalamin group was significantly greater than that in the placebo group (P=.044). The change in the 10-microg cyanocobalamin group was not significantly different from that in the placebo group (P=.186). Eight of 10 subjects in each treatment group were classified as responders, compared with two of 11 in the placebo group (P=.004). Homocysteine levels fell in patients receiving cyanocobalamin, but this fall failed to reach statistical significance. There were no significant changes in the other parameters measured. CONCLUSION: Cyanocobalamin supplementation of 50 microg but not 10 microg daily produced a significant increase in serum vitamin B12. This result has implications for the management of patients with subnormal or borderline serum vitamin B12 concentrations and for food fortification with vitamin B12.     

Folate administration reduces circulating homocysteine levels in NIDDM patients on long-term metformin treatment

OBJECTIVES: Metformin treatment increases circulating homocysteine levels. We studied whether administration of folate reduces serum total homocysteine levels in patients on long-term metformin treatment. DESIGN: A prospective, randomized, double-blind, placebo-controlled study lasting for 12 weeks and taking place in a university hospital setting. SUBJECTS: Thirty patients treated with a metformin dose of at least 1000 mg day-1 for a minimum of 1 year were included. At baseline serum total homocysteine levels were within the reference range. One patient who withdrew and one who died were excluded from the statistical evaluation. Twenty-six of the remaining patients suffered from NIDDM, the other two from hyperlipidaemia. INTERVENTION: Patients were randomized into two groups at week 0. The folate group received 0.25 mg day-1 of folate in addition to 60 mg day-1 of Fe2+, while the placebo group received only 60 mg day-1 of Fe2+. MAIN OUTCOME MEASURES: Fasting homocysteine, cysteine, cysteinylglycine, vitamin B12 and folate were measured at week 0, 4 and 12. Changes from week 0 to week 4 and from week 0 to week 12 were calculated. RESULTS: Folate administration reduced serum levels of total homocysteine in the folate group as compared with the placebo group by 13.9% (P < 0.01) and 21.7% (P < 0.001) at week 4 and 12, respectively. In the folate group versus the placebo group serum levels of vitamin B12 increased by 9.9% (P = 0.010) and 9.6% (P = 0.043) while folate levels increased by 96.9 and 89.9% at week 4 and 12, respectively. CONCLUSION: The present study indicates that the homocysteine-increasing effect of metformin can be counteracted by folate administration.     

Effects of short-term treatment with metformin on markers of endothelial function and inflammatory activity in type 2 diabetes mellitus: a randomized, placebo-controlled trial

OBJECTIVES: The UK Prospective Diabetes Study (UKPDS) showed that treatment with metformin decreases macrovascular morbidity and mortality independent of glycaemic control. We hypothesized that metformin may achieve this by improving endothelial function and chronic, low-grade inflammation. Data on this issue are scarce and we therefore tested, in the setting of a randomized, placebo-controlled trial, whether metformin can affect endothelial function and low-grade inflammation. DESIGN: The Hyperinsulinaemia the Outcome of its Metabolic Effects (HOME) trial is a double-blind trial, in which all patients were randomized to receive either metformin or placebo in addition to insulin therapy. At the beginning and the end of a 16-week treatment period fasting blood samples were drawn and a physical examination was carried out. SETTING: The trial was conducted in the outpatient clinics of three nonacademic hospitals (Hoogeveen, Meppel and Coevorden; the Netherlands). SUBJECTS: Patients were included if they were between 30 and 80 years of age; had received a diagnosis of diabetes after the age of 25; had never had an episode of ketoacidosis; and their blood glucose-lowering treatment previously consisted of oral agents but now only consisted of either insulin (n = 345) or insulin and metformin (n = 45). We excluded pregnant women and women trying to become pregnant, patients with a Cockroft-Gault-estimated creatinine clearance <50 mL min(-1), or low plasma cholinesterase (reference value <3.5 units L(-1)), patients with congestive heart failure (New York Heart Association class III/IV), or patients with other serious medical or psychiatric disease. A total of 745 eligible patients were approached; 390 gave informed consent and were randomized (196 metformin, 194 placebo). About 353 patients completed 16 weeks of treatment (171 metformin, 182 placebo). MAIN OUTCOME MEASURES: The HOME trial was designed to study the metabolic and cardiovascular effects of metformin during a follow-up of 4 years. Presented here are the results of an interim analysis after 16 weeks of treatment. RESULTS: When compared with placebo, metformin treatment was associated with an increase in urinary albumin excretion of 21% (-1 to +48; P = 0.06); a decrease in plasma von Willebrand factor of 6% (-10 to -2; P = 0.0007); a decrease in soluble vascular cell adhesion molecule-1 of 4% (-7 to -2; P = 0.0002); a decrease in soluble E-selectin of 6% (-10 to -2; P = 0.008); a decrease in tissue-type plasminogen activator of 16% (-20 to -12; P < 0.0001); and a decrease in plasminogen activator inhibitor-1 of 20% (-27 to -10; P = 0.0001). These changes could not be explained by metformin-associated changes in glycaemic control, body weight or insulin dose. Markers of inflammation, i.e. C-reactive protein and soluble intercellular adhesion molecule-1, did not change with metformin treatment. CONCLUSIONS: In patients with type 2 diabetes treated with insulin, metformin treatment was associated with improvement of endothelial function, which was largely unrelated to changes in glycaemic control, but not with improvement of chronic, low-grade inflammation.     

Effects of metformin or rosiglitazone on serum concentrations of homocysteine, folate, and vitamin B12 in patients with type 2 diabetes mellitus

OBJECTIVES: Metformin is widely used in patients with type 2 diabetes but may decrease vitamin B(12) levels and increase levels of homocysteine (Hcy), a cardiovascular risk factor. Rosiglitazone, a peroxisome proliferator-activated receptor-gamma agonist, may reduce markers of inflammation. We investigated whether 6 weeks' treatment with metformin or rosiglitazone affects serum concentrations of Hcy, folate, or vitamin B(12) in subjects with newly diagnosed type 2 diabetes compared with controls. METHODS: We examined 165 patients with type 2 diabetes. Fasting blood samples, a physical examination, and a complete medical history were performed at the beginning and at the end of the treatment. All blood samples were obtained after a 12-h fast. RESULTS: After treatment, metformin use was associated with an increase in levels of Hcy by 2.36 micromol/l and decreases in folate and vitamin B(12) concentrations by -1.04 ng/ml and -20.17 pg/ml. During rosiglitazone treatment, Hcy levels decreased by -0.92 micromol/l; folate and vitamin B(12) levels remained unchanged. Metformin and rosiglitazone significantly decreased levels of triglyceride (TG), low-density lipoprotein (LDL), total cholesterol (total-C), HbA1c, insulin, and homeostasis model assessment (HOMA). Metformin also significantly decreased body weight. In controls, there was no change in Hcy, folic acid, vitamin B(12), TG, LDL, total-C, HbA1c, insulin, or HOMA levels. Homocysteine change did not correlate with insulin, folate, or vitamin B(12) changes in the metformin and rosiglitazone groups. CONCLUSIONS: In patients with type 2 diabetes, metformin reduces levels of folate and vitamin B(12) and increases Hcy. Conversely, rosiglitazone decreases Hcy levels in this time period. The clinical significance of these findings remains to be investigated.     

Prevalence of low vitamin B12 and high homocysteine in serum in an elderly male population: association with atrophic gastritis and Helicobacter pylori infection

Background: Deficiency of vitamin B12 raises the serum and tissue levels of homocysteine. Atrophic corpus gastritis results in impaired secretion of intrinsic factor and may lead to malabsorption of vitamin B12 in the intestine. We examined how common an undiagnosed vitamin B12 deficiency is among elderly men in the general population and, in particular, how often this deficiency is related to atrophic corpus gastritis. Methods: The serum level of pepsinogen I (S‐PGI) was assayed in a population‐based sample of 12,252 men (age 51–65 years) from two cities in Finland. In this sample, all 635 men with S‐PGI?n?=?402) with S‐PGI?≥?50?μg/l. Serum levels of vitamin B12 (S‐B12), folate (S‐Fol), total homocysteine (S‐Hcy) and Helicobacter pylori antibodies (S‐HpAb) were assayed in all, or in large subsamples, of the men in Series A and C. Results: The men in Series A had significantly lower S‐B12 and S‐Fol levels than those in Series C. In Series A, 172 of 613 men tested (28%) had S‐B12?P?P??15?μmol/l was 27% in Series A and 15% in Series C (P?2 =?4.63). Among subjects with S‐B12?P?P?Conclusions: Low S‐B12 related to atrophic corpus gastritis is relatively common (prevalence 2.5%) among elderly males in the general population. An ongoing H. pylori infection occurs in three‐fourths of these cases.     

Elevated plasma homocysteine concentrations as a predictor of steatohepatitis in patients with non-alcoholic fatty liver disease

BACKGROUND: Although steatosis is common in patients with severe hyperhomocysteinemia due to deficiency of cystathionine beta-synthase, there are no satisfactory data on homocysteine concentrations in patients with non-alcoholic fatty liver disease. The main aim of the present study was to evaluate the clinical significance of plasma homocysteine concentrations in patients with non-alcoholic fatty liver disease. METHODS: Seventy-one non-alcoholic fatty liver disease patients, 36 patients with chronic viral hepatitis and 30 healthy persons were enrolled in the study. Homocysteine levels were measured by high-performance liquid chromatography. Insulin, folate, vitamin B(12) and lipoprotein levels were also determined in all groups. RESULTS: Homocysteine in the non-alcoholic fatty liver disease group was found to be significantly higher than other groups. Homocysteine was found to be significantly higher in the non-alcoholic steatohepatitis group when compared with simple steatosis group. A positive correlation was found between homocysteine and triglyceride, very-low-density-lipoprotein (VLDL) cholesterol, insulin, and index of insulin resistance in the non-alcoholic fatty liver disease group, and a negative correlation was found between homocysteine and folate, or vitamin B(12) in all groups. The homocysteine threshold for the prediction of steatohepatitis was 11.935 ng/mL. Furthermore; plasma homocysteine was a statistically significant predictor for severity of necroinflammatory activity in non-alcoholic steatohepatitis. CONCLUSIONS: The plasma homocysteine concentrations were significantly higher in patients with non-alcoholic fatty liver disease, while the concentrations were not affected by chronic viral hepatitis. Plasma homocysteine is a parameter for discriminating steatohepatitis from simple steatosis. Determining the plasma homocysteine concentrations may facilitate selection of steatosis patients in whom a liver biopsy should be performed.     

Continuing metformin when starting insulin in patients with Type 2 diabetes: a double-blind randomized placebo-controlled trial.

AIMS: To test the effect of continuing metformin on weight gain and glycaemic control in patients with poorly controlled Type 2 diabetes who need to start insulin. METHODS: Patients with Type 2 diabetes on maximum tolerated oral agents referred for insulin conversion were recruited from hospital diabetes clinics into a double-blind randomized placebo-controlled trial. The 183 participants received metformin or placebo, titrated up to 2 g a day or maximum tolerated dose, with insulin started according to local practice. The main outcome measures were weight change over 12 months, HbA1c, insulin dose, frequency of hypoglycaemia, treatment satisfaction, and well-being. RESULTS: Over 12 months, metformin was associated with less weight gain than placebo [mean 6.1 kg vs. 7.6 kg; adjusted difference 1.5 kg (95% confidence interval 0.2-2.9); P=0.02], a greater reduction in HbA1c[1.5% vs. 1.3%; adjusted difference 0.5% (0.1-0.9); P=0.02] and a lower insulin requirement [62 units vs. 86; adjusted difference 25 units (15-34); P<0.001], but also more hypoglycaemia [relative risk of any episode 1.24 (1.02-1.1); P=0.03]. Treatment satisfaction improved more in patients on metformin than on placebo (P<0.001), as did the positive well-being score (P=0.02). CONCLUSIONS: Metformin decreases weight gain, lowers insulin requirement, and improves glycaemic control, and should be continued in patients with Type 2 diabetes who transfer to insulin.     

Optimization of folic acid, vitamin B(12), and vitamin B(6) supplements in pediatric patients with sickle cell disease

Using homocysteine as a functional marker, we determined optimal folic acid, vitamin B(12), and vitamin B(6) dosages in 21 pediatric sickle cell disease (SCD) patients (11 HbSS, 10 HbSC; 7-16 years). Daily supplements of folic acid (400, 700, or 1,000 microg), vitamin B(12) (1, 3, or 5 U.S. 1989 RDA), and vitamin B(6) (1 or 3 U.S. 1989 RDA) were gradually increased in an 82-week dose-escalation study. Blood was taken at 9 occasions for measurements of erythrocyte (RBC) and serum folate, plasma vitamin B(12), whole-blood vitamin B(6), and plasma homocysteine. Augmentation of folic acid from 700 to 1,000 microg and vitamin B(12) from 3 to 5 RDA did not further decrease homocysteine. Percentages of patients exhibiting significant individual homocysteine decreases amounted to 43% (folic acid from 0 to 400 microg, vitamins B(12) and B(6) from 0 to 1 RDA), 14% (folic acid from 400 to 700 microg), 24% (vitamin B(12) from 1 to 3 RDA), and 18% (vitamin B(6) from 1 to 3 RDA ). The lowest plasma homocysteine at 82 weeks was 5.9 +/- 2.2 micromol/L. Patients with HbSS had higher RBC folate than HbSC. The entire group exhibited an inverse relation between RBC folate and hemoglobin. We conclude that RBC folate is less valuable for folate status assessment in SCD patients. Optimal dosages are as follows: 700 microg folic acid (3.5-7 U.S. 1989 RDA), 3 U.S. 1989 RDA vitamin B(12) (4.2-6.0 microg), and 3 U.S. 1989 RDA vitamin B(6) (4.2-6.0 mg). A practical daily combination is 1 mg folic acid (4.3-8.5 U.S. 1998 RDA when taken with meals), 6 microg vitamin B(12) (2.5-5 U.S. 1998 RDA), and 6 mg vitamin B(6) (4.6-10 U.S. 1998 RDA). This combination may by simple and relatively inexpensive means reduce these patients' inherently high risk of endothelial damage.     

Folate, Vitamin B12, Homocysteine, and Depressive Symptoms in a Population Sample of Older Chinese Adults

OBJECTIVES: To investigate the independent associations between folate, B12, and homocysteine levels and depressive symptoms in older adults.
DESIGN: Cross-sectional study.
SETTING: Resident population in southeast Singapore.
PARTICIPANTS: Six hundred sixty-nine community-living noninstitutionalized Chinese adults aged 55 and older.
MEASUREMENTS: Laboratory values of folate, vitamin B12, and homocysteine were examined for their independent relationships with depressive symptoms (Geriatric Depression Scale (GDS) score ≥5).
RESULTS: Respondents with depression (n=178) had lower mean serum folate concentrations (21.5 nmol/L) than those without (n=491, 24.0 nmol/L, P =.04). There was a linear relationship between descending quartiles of folate concentrations and increasing odds of association with depressive symptoms, independent of other risk factors (demographic, psychosocial, alcohol and smoking, chronic morbidity, functional status, nutritional risk, albumin, anemia, depression-inducing medications, use of antidepressants and vitamin supplements), including B12 and homocysteine ( P for trend=.02). The odds ratio (OR) of association between low folate (lowest quartile: <14.6 nmol/L) and depressive symptoms independent of other risk factors, including homocysteine and B12, was 1.72 (95% confidence interval (CI)=1.11–2.66). Vitamin B12 across a range of values did not show a linear association, but B12 deficiency (<180 pmol/L) appeared to be significantly associated with depressive symptoms (OR=2.68, 95% CI=1.20–6.00), independent of folate and homocysteine.
CONCLUSION: Decreasing and low levels of serum folate and deficient levels of B12 were associated with greater risk of depressive symptoms in older Chinese adults.     

二甲双胍对糖尿病患者血清同型半胱氨酸和维生素B12水平的影响

目的 探讨T2DM患者二甲双胍治疗后血清同型半胱氨酸(Hcy)、维生素B12(Vit B12)、叶酸(FA)水平的变化.方法 44例T2DM患者在原治疗的基础上口服二甲双胍,治疗前和治疗半年后测定血清Hcy、Vit B12、FA水平.结果 口服二甲双胍半年后,血清Vit B12、FA水平下降,Hcy水平升高,其升高与二甲双胍使用剂量、Vit B12、FA下降相关.结论 二甲双胍口服半年可降低T2DM患者Vit B12、FA水平,升高血清Hcy水平.     

An assessment of serum vitamin B12 and folate in patients with Crohn’s disease

Crohn’s disease is a chronic inflammatory condition that can involve any area in the gastrointestinal tract often involving the distal ileum where vitamin B12 is specifically absorbed. The aim of this study was to ascertain serum vitamin B12 and folate levels in order to investigate the correlation among these vitamin levels and disease activation, localization, duration and age at the onset of the disease.Study population included 103 patients with Crohn’s disease and a healthy control group of 114 individuals. C-reactive protein, vitamin B12, folate levels were studied along with hemogram analyses. The results were evaluated in statistical comparisons. While serum vitamin B12 levels and serum folate levels were 161.9 ± 63.2(73–496) pg/mL and 4.9 ± 1.4(1.2–9.4) ng/mL in the Crohn’s patient group respectively, they were 321.7 ± 126.3(85–680) pg/mL and 7.6 ± 3.8(3–25.1) ng/mL in the control group respectively. Vitamin B12 and folate levels were distinctly lower in patients with Chron’s disease than those of the control group (P < .001). The intragroup analysis of the patient group revealed that low vitamin B12 levels were significantly lower in the moderate group classified according to the Crohn’s Disease Activity Index (P < .001), along with those in the L1 group with terminal/distal ileal involvement (P < .001).Vitamin B12 and folate deficiencies are quite prevalent in patients with Crohn’s disease while this condition can lead to various complications and they prove to be important risk factors associated especially with thrombosis and its complications. Patients must be regularly followed-up for vitamin B12 and folate levels to supplement them where needed.     

Food-bound B12 absorption and serum total homocysteine in patients with low serum B12 levels

This study was undertaken to determine whether measurements of serum total homocysteine (Hcys) and bound B12 absorption are useful in determining which patients with low- or low-normal levels of serum B12 are B12 deficient. In 40 patients with low or borderline serum levels of B12, food-bound B12 absorptions were determined using a body counter in an iron room, and were related to serum total Hcys levels. Food-bound B12 absorption was decreased in 16 patients and in an additional four, absorption of the free vitamin was also decreased. Homocysteine levels were elevated in four of the 16; in three of the four who had both decreased bound and free B12 absorptions, Hcys was elevated. If elevation of the Hcys level indicates tissue deficiency of B12, the 75% incidence of normal levels of Hcys in these patients with low food-bound B12 absorptions suggests the existence of a cohort of patients who may be at risk to develop, but have not yet developed, B12 deficiency. Only long term follow-up will reveal how many ultimately will become B12 deficient. Am. J. Hematol. 59:42–45, 1998. © 1998 Wiley-Liss, Inc.     

Adding metformin versus insulin dose increase in insulin-treated but poorly controlled Type 2 diabetes mellitus: an open-label randomized trial

To compare the effect of adding metformin to insulin therapy with a moderate increase in insulin dose alone in insulin-treated, poorly controlled Type 2 diabetic patients, 47 consecutive such patients (baseline daily dose >0.5 IU kg⁻¹ and HbA_1c >8 %) were openly randomized either to a combination of their previous insulin schedule plus metformin (2.55 g daily in three divided doses, n = 24) or to a moderate insulin dose increase (20 % of baseline, n = 23). The patient status/biochemical profile was assessed at entry and at 4 months. Among those assigned to insulin + metformin, 18 took the drug. Upon an intention-to-treat basis, patients assigned to insulin dose increase had a statistically significant weight gain (1.16 + 1.9 vs 0.3 ± 4.5 kg, p < 0.05). Patients assigned to the insulin + metformin regimen experienced a significantly greater fall in HbA_1c (−1.87 ± 2.16 vs 0.03 ± 1.68 %, p < 0.01), total cholesterol (−0.56 ± 0.89 vs 0.14 ± 0.72 mmol l⁻¹, p < 0.05) and LDL-cholesterol (−0.51 ± 0.73 vs 0.19 ± 0.6 mmol l⁻¹, p < 0.01). These data suggest that adding metformin to insulin in poorly controlled Type 2 DM patients offers an advantage in terms of glycaemic control and lipid plasma profile. Copyright © 1998 John Wiley & Sons, Ltd.     

Homocysteine and vitamin B(12) concentrations and mortality rates in type 2 diabetes

OBJECTIVE: To assess the role of homocysteine as a risk factor for mortality in diabetic subjects. METHODS: Homocysteine, vitamin B(12), and folate concentrations were measured in stored sera of 396 diabetic Pima Indians aged > or = 40 years when examined between 1982 and 1985. Vital status was assessed through 2001. RESULTS AND CONCLUSIONS: Over a median follow-up of 15.7 years, there were 221 deaths-76 were due to cardiovascular disease (CVD), 36 to diabetes/nephropathy and 34 to infections. Homocysteine was positively associated with mortality from all causes (hazard rate ratio (HRR) for highest versus lowest tertile of homocysteine = 1.70, 95% confidence interval (CI) 1.18-2.46), from diabetes/nephropathy (HRR = 2.39, 95% CI 0.94-6.11) and from infectious diseases (HRR = 3.39, 95% CI 1.19-9.70), but not from CVD (HRR = 1.16, 95% CI 0.62-2.17) after adjustment for age, sex and diabetes duration. Homocysteine correlated with serum creatinine (r = 0.50), and the relationships with mortality rates were not significant after adjustment for creatinine. Vitamin B(12) was positively associated with all-cause mortality (HRR for 100 pg/mL difference adjusted for age, sex and diabetes duration = 1.15, 95% CI 1.08-1.22) and death from diabetes/nephropathy (HRR = 1.27, 95% CI 1.10-1.46). The association between homocysteine and mortality in type 2 diabetes is not causal, but is confounded by renal disease in Pima Indians.