Related Articles

OBJECTIVE

Homocysteinemia may play an etiologic role in the pathogenesis of type 2 diabetes by promoting oxidative stress, systemic inflammation, and endothelial dysfunction. We investigated whether homocysteine-lowering treatment by B vitamin supplementation prevents the risk of type 2 diabetes.

RESEARCH DESIGN AND METHODS

The Women's Antioxidant and Folic Acid Cardiovascular Study (WAFACS), a randomized, double-blind, placebo-controlled trial of 5,442 female health professionals aged ≥40 years with a history of cardiovascular disease (CVD) or three or more CVD risk factors, included 4,252 women free of diabetes at baseline. Participants were randomly assigned to either an active treatment group (daily intake of a combination pill of 2.5 mg folic acid, 50 mg vitamin B6, and 1 mg vitamin B12) or to the placebo group.

RESULTS

During a median follow-up of 7.3 years, 504 women had an incident diagnosis of type 2 diabetes. Overall, there was no significant difference between the active treatment group and the placebo group in diabetes risk (relative risk 0.94 [95% CI 0.79–1.11]; P = 0.46), despite significant lowering of homocysteine levels. Also, there was no evidence for effect modifications by baseline intakes of dietary folate, vitamin B6, and vitamin B12. In a sensitivity analysis, the null result remained for women compliant with their study pills (0.92 [0.76–1.10]; P = 0.36).

CONCLUSIONS

Lowering homocysteine levels by daily supplementation with folic acid and vitamins B6 and B12 did not reduce the risk of developing type 2 diabetes among women at high risk for CVD.

Conclusion

There is considerable epidemiological evidence, which confirms the importance of plasma homocysteine as a powerful predictor of future risk of coronary heart disease and other complications of atherosclerosis. Treatment of hyperhomocysteinemia varies with the underlying cause. However, an inexpensive vitamin supplementation with folic acid, vitamin B12 and vitamin B 6 is generally effective in reducing homocysteine concentrations. Several randomised, controlled trials evaluating the effects of folic acid based supplements on homocysteine concentrations have been conducted over the last decade. In most patients, folic acid alone, and in combination of vitamin B12 and B6, has been shown to reduce homocysteine concentrations within four to six weeks after the initiation of therapy (34).

However, no study has yet demonstrated that lowering of homocysteine by vitamin supplementation decreases the cardiovascular morbidity or mortality. Avoidance of excessive meat intake and increased consumption of fresh vegetables and fruits is a dietary measure, which has many health benefits, including a potential to reduce elevated homocysteine levels. The other reasonable approach is to determine levels of fasting homocysteine in high risk patients and it may be advisable to increase their intake of vitamin fortified foods and/or to suggest the daily use of supplemental vitamins. Several large scale randomised trials like Heart Outcomes Prevention Evaluation (HOPE-2) Study, Mcmaster University, Canada, Study of the Effectiveness of Additional Reductions in Cholesterol and Homocysteine (SERCH), Clinical Trial Service Unit, Oxford, U.K, Cambridge Heart Antioxidant Study (CHAOS-2) University of Cambridge, U.K, Bergen Vitamin Study, University of Bergen Norway, Women's Antioxidant and Cardiovascular Disease Study (WACS) Harvard Medical School, U.S.A, Prevention with a combined inhibitor and folate in Coronary Heart Disease (PACIFIC) study, University of Sydney, Australia, and many others are ongoing to assess the effect of homocysteine—lowering by vitamin supplementation on risk of vascular disease.

Elevated plasma concentrations of homocysteine, a sulfur-containing amino acid, are a risk factor for coronary, cerebral and peripheral artery disease. Next to other factors, drugs used for the prevention or treatment of cardiovascular disease may modulate plasma homocysteine levels. Thus, a drug induced homocysteine increase may counteract the desired cardioprotective effect. The aim is to summarize the current knowledge on the effect of two important classes of drugs, lipid-lowering drugs and anti-hypertensive drugs, on homocysteine metabolism. Among the lipid-lowering drugs, especially the fibric acid derivatives, which are used for treatment of hypertriglyceridemia and low HDL-cholesterol, are associated with an increase of homocysteine by 20%–50%. This increase can be reduced, but not totally avoided by the addition of folic acid, vitamin B12 and B6 to fibrates. HMG-CoA reductase inhibitors (statins) do not influence homocysteine concentrations substantially. The effects of nicotinic acid and n3-fatty acids on the homocysteine concentrations are less clear, more studies are necessary to clarify their influence on homocysteine. Antihypertensive drugs have also been studied with respect to homocysteine metabolism. A homocysteine increase has been shown after treatment with hydrochlorothiazide, a lowering was observed after treatment with ß-blockers, but no effect with ACE-inhibitors. The clinical significance of the homocysteine elevation by fibrates and thiazides is not clear. However, individual patients use these drugs for long time, indicating that even moderate increases may be important.

Objectives

Endothelial dysfunction is a common feature of type 2 diabetes. Recent studies suggest that the B-vitamin folic acid exerts direct beneficial effects on endothelial function, beyond the well known homocysteine lowering effects. Therefore, folic acid might represent a novel “biomarker” of endothelial function. We sought to determine whether plasma levels of folic acid determine endothelial-dependent vasodilation in patients with type 2 diabetes.

Methods

Forearm arterial blood flow (FABF) was measured at baseline and during intrabrachial infusion of the endothelial-dependent vasodilator acetylcholine (15 μg/min) and the endothelial-independent vasodilator sodium nitroprusside (2 μg/min) in 26 type 2 diabetic patients (age 56.5 ± 0.9 years, means ± SEM) with no history of cardiovascular disease.

Results

FABF ratio (ie, the ratio between the infused and control forearm FABF) significantly increased during acetylcholine (1.10 ± 0.04 vs 1.52 ± 0.07, p < 0.001) and sodium nitroprusside (1.12 ± 0.11 vs 1.62 ± 0.06, p < 0.001) infusions. After correcting for age, gender, diabetes duration, smoking, hypertension, body mass index, microalbuminuria, glycated hemoglobin, low-density lipoprotein cholesterol, and homocysteine, multiple regression analysis showed that plasma folic acid concentration was the only independent determinant (p = 0.037, R2 = 0.22) of acetylcholine-mediated, but not sodium nitroprusside-mediated, vasodilatation.

Conclusions

Folic acid plasma concentrations determine endothelium-mediated vasodilatation in patients with type 2 diabetes. These results support the hypothesis of a direct effect of folic acid on endothelial function and the rationale for interventions aimed at increasing folic acid levels to reduce cardiovascular risk.

Context

Observational epidemiologic studies indicate a direct association between homocysteine concentration in the blood and risk of age-related macular degeneration (AMD), but randomized trial data to examine the effect of homocysteine-lowering in AMD are lacking.

Objective

To examine incidence of AMD in a trial of folic acid/vitamin B6/vitamin B12.

Design

Randomized, double-masked, placebo-controlled trial.

Participants

5,442 female health professionals aged 40 years or older with preexisting cardiovascular disease (CVD) or 3 or more CVD risk factors. A total of 5,205 of these women did not have a diagnosis of AMD at baseline and were included in this analysis.

Intervention

Participants were randomly assigned to receive a combination of folic acid (2.5 mg/d), vitamin B6 (50 mg/d), and vitamin B12 (1 mg/d), or placebo.

Main Outcome Measures

Total AMD, defined as a self-report documented by medical record evidence of an initial diagnosis after randomization, and visually-significant AMD, defined as confirmed incident AMD with visual acuity of 20/30 or worse attributable to this condition.

Results

After an average of 7.3 years of treatment and follow-up, there were 55 cases of AMD in the folic acid/B6/B12 group and 82 in the placebo group (relative risk [RR], 0.66; 95% confidence interval [CI], 0.47–0.93; p=0.02). For visually-significant AMD, there were 26 cases in the folic acid/B6/B12 group and 44 in the placebo group (RR, 0.59; 95% CI, 0.36–0.95; p=0.03).

Conclusions

These randomized trial data from a large cohort of women at high risk of CVD indicate that daily supplementation with folic acid/B6/B12 may reduce the risk of AMD.

Background

Betaine (trimethylglycine) lowers plasma homocysteine, a possible risk factor for cardiovascular disease. However, studies in renal patients and in obese individuals who are on a weight-loss diet suggest that betaine supplementation raises blood cholesterol; data in healthy individuals are lacking. Such an effect on cholesterol would counteract any favourable effect on homocysteine. We therefore investigated the effect of betaine, of its precursor choline in the form of phosphatidylcholine, and of the classical homocysteine-lowering vitamin folic acid on blood lipid concentrations in healthy humans.

Methods and Findings

We measured blood lipids in four placebo-controlled, randomised intervention studies that examined the effect of betaine (three studies, n = 151), folic acid (two studies, n = 75), and phosphatidylcholine (one study, n = 26) on plasma homocysteine concentrations. We combined blood lipid data from the individual studies and calculated a weighted mean change in blood lipid concentrations relative to placebo. Betaine supplementation (6 g/d) for 6 wk increased blood LDL cholesterol concentrations by 0.36 mmol/l (95% confidence interval: 0.25–0.46), and triacylglycerol concentrations by 0.14 mmol/l (0.04–0.23) relative to placebo. The ratio of total to HDL cholesterol increased by 0.23 (0.14–0.32). Concentrations of HDL cholesterol were not affected. Doses of betaine lower than 6 g/d also raised LDL cholesterol, but these changes were not statistically significant. Further, the effect of betaine on LDL cholesterol was already evident after 2 wk of intervention. Phosphatidylcholine supplementation (providing approximately 2.6 g/d of choline) for 2 wk increased triacylglycerol concentrations by 0.14 mmol/l (0.06–0.21), but did not affect cholesterol concentrations. Folic acid supplementation (0.8 mg/d) had no effect on lipid concentrations.

Conclusions

Betaine supplementation increased blood LDL cholesterol and triacylglycerol concentrations in healthy humans, which agrees with the limited previous data. The adverse effects on blood lipids may undo the potential benefits for cardiovascular health of betaine supplementation through homocysteine lowering. In our study phosphatidylcholine supplementation slightly increased triacylglycerol concentrations in healthy humans. Previous studies of phosphatidylcholine and blood lipids showed no clear effect. Thus the effect of phosphatidylcholine supplementation on blood lipids remains inconclusive, but is probably not large.

Folic acid supplementation does not seem to affect blood lipids and therefore remains the preferred treatment for lowering of blood homocysteine concentrations.

Lowering homocysteine might reduce the risk for heart disease. Betaine seems to have an adverse effect on blood lipids. This would make it less suitable than folic acid, which does not affect blood lipids.

Objective: To determine the size of reduction in homocysteine concentrations produced by dietary supplementation with folic acid and with vitamins B-12 or B-6.

Design: Meta-analysis of randomised controlled trials that assessed the effects of folic acid based supplements on blood homocysteine concentrations. Multivariate regression analysis was used to determine the effects on homocysteine concentrations of different doses of folic acid and of the addition of vitamin B-12 or B-6.

Subjects: Individual data on 1114 people included in 12 trials.

Findings: The proportional and absolute reductions in blood homocysteine produced by folic acid supplements were greater at higher pretreatment blood homocysteine concentrations (P<0.001) and at lower pretreatment blood folate concentrations (P<0.001). After standardisation to pretreatment blood concentrations of homocysteine of 12 μmol/l and of folate of 12 nmol/l (approximate average concentrations for Western populations), dietary folic acid reduced blood homocysteine concentrations by 25% (95% confidence interval 23% to 28%; P<0.001), with similar effects in the range of 0.5-5 mg folic acid daily. Vitamin B-12 (mean 0.5 mg daily) produced an additional 7% (3% to 10%) reduction in blood homocysteine. Vitamin B-6 (mean 16.5 mg daily) did not have a significant additional effect.

Conclusions: Typically in Western populations, daily supplementation with both 0.5-5 mg folic acid and about 0.5 mg vitamin B-12 would be expected to reduce blood homocysteine concentrations by about a quarter to a third (for example, from about 12 μmol/l to 8-9 μmol/l). Large scale randomised trials of such regimens in high risk populations are now needed to determine whether lowering blood homocysteine concentrations reduces the risk of vascular disease.

Key messages Higher blood homocysteine concentrations seem to be associated with higher risks of occlusive vascular disease and with lower blood concentrations of folate and vitamins B-12 and B-6 Proportional and absolute reductions in blood homocysteine concentrations with folic acid supplements are greater at higher pretreatment blood homocysteine concentrations and at lower pretreatment blood folate concentrations In typical Western populations, supplementation with both 0.5-5 mg daily folic acid and about 0.5 mg daily vitamin B-12 should reduce blood homocysteine concentrations by about a quarter to a third Large scale randomised trials of such regimens in people at high risk are now needed to determine whether lowering blood homocysteine concentrations reduces the risk of vascular disease

Background

High homocysteine levels may be neurotoxic and contribute to cognitive decline in older persons.

Objective

Examine the effect of supplementation with folic acid, vitamin B12 and vitamin B6 on cognitive change among women with cardiovascular disease (CVD) or CVD risk factors.

Design

The Women's Antioxidant and Folic Acid Cardiovascular Study is a randomized, placebo-controlled trial to test a combination of B vitamins (folic acid 2.5 mg, vitamin B6 50 mg, and vitamin B12 1 mg, daily) for secondary prevention of CVD. Randomization took place among 5,442 female health professionals, 40+ years, with CVD or at least three coronary risk factors in 1998 (after folic acid fortification began in the US). Shortly after randomization (mean=1.2 years), a cognitive function substudy was initiated among 2009 participants aged 65+ years. Telephone cognitive function testing was administered up to four times over 5.4 years with 5 tests of general cognition, verbal memory and category fluency. Repeated measures analyses were conducted. The primary outcome was a global composite score averaging all tests.

Results

Mean cognitive change from baseline did not differ between the B vitamin and placebo groups (difference in change in global score= 0.03, 95% CI −0.03, 0.08; p=0.30). However, supplementation appeared to confer benefits in preserving cognition among women with low baseline dietary intake of B vitamins.

Conclusions

Combined B vitamin supplementation did not delay cognitive decline among women with CVD or CVD risk factors. Possible cognitive benefits of supplementation among women with low dietary intake of B vitamins warrant further study.

Summary

Background

Previous studies have suggested that any benefits of folic acid-based therapy to lower serum homocysteine in prevention of cardiovascular events might be offset by concomitant use of antiplatelet therapy. We aimed to establish whether there is an interaction between antiplatelet therapy and the effects of folic acid-based homocysteine-lowering therapy on major vascular events in patients with stroke or transient ischaemic attack enrolled in the vitamins to prevent stroke (VITATOPS) trial.

Methods

In the VITATOPS trial, 8164 patients with recent stroke or transient ischaemic attack were randomly allocated to double-blind treatment with one tablet daily of placebo or B vitamins (2 mg folic acid, 25 mg vitamin B6, and 500 μg vitamin B12) and followed up for a median 3·4 years (IQR 2·0–5·5) for the primary composite outcome of stroke, myocardial infarction, or death from vascular causes. In our post-hoc analysis of the interaction between antiplatelet therapy and the effects of treatment with B vitamins on the primary outcome, we used Cox proportional hazards regression before and after adjusting for imbalances in baseline prognostic factors in participants who were and were not taking antiplatelet drugs at baseline and in participants assigned to receive B vitamins or placebo. We also assessed the interaction in different subgroups of patients and different secondary outcomes. The VITATOPS trial is registered with ClinicalTrials.gov, number NCT00097669, and Current Controlled Trials, number ISRCTN74743444.

Findings

At baseline, 6609 patients were taking antiplatelet therapy and 1463 were not. Patients not receiving antiplatelet therapy were more likely to be younger, east Asian, and disabled, to have a haemorrhagic stroke or cardioembolic ischaemic stroke, and to have a history of hypertension or atrial fibrillation. They were less likely to be smokers and to have a history of peripheral artery disease, hypercholesterolaemia, diabetes, ischaemic heart disease, and a revascularisation procedure. Of the participants taking antiplatelet drugs at baseline, B vitamins had no significant effect on the primary outcome (488 patients in the B-vitamins group [15%] vs 519 in the placebo group [16%]; hazard ratio [HR] 0·94, 95% CI 0·83–1·07). By contrast, of the participants not taking antiplatelet drugs at baseline, B vitamins had a significant effect on the primary outcome (123 in the B-vitamins group [17%] vs 153 in the placebo group [21%]; HR 0·76, 0·60–0·96). The interaction between antiplatelet therapy and the effect of B vitamins on the primary outcome was significant after adjusting for imbalance in the baseline variables (adjusted p for interaction=0·0204).

Interpretation

Our findings support the hypothesis that antiplatelet therapy modifies the potential benefits of lowering homocysteine with B-vitamin supplementation in the secondary prevention of major vascular events. If validated, B vitamins might have a role in the prevention of ischaemic events in high-risk individuals with an allergy, intolerance, or lack of indication for antiplatelet therapy.

Funding

Australia National Health and Medical Research Council, UK Medical Research Council, Singapore Biomedical Research Council, and Singapore National Medical Research Council.

Background and objective

There is an ongoing debate on the role of the cytotoxic aminoacid homocysteine as a causal risk factor for the development of coronary heart disease. Results from multiple case control-studies demonstrate, that there is a strong association between high plasma levels of homoysteine and prevalent coronary heart disease, independent of other classic risk factors. Furthermore, results from interventional studies point out that elevated plasma levels of homocysteine may effectively be lowered by the intake of folic acid and B vitamins. In order to use this information for the construction of a new preventive strategy against coronary heart disease, more information is needed: first, whether homocysteine actually is a causal risk factor with relevant predictive properties and, second, whether by lowering elevated homocysteine plasma concentrations cardiac morbidity can be reduced. Currently in Germany the determination of homocysteine plasma levels is reimbursed for by statutory health insurance in patients with manifest coronary heart disease and in patients at high risk for coronary heart disease but not for screening purposes in asymptomatic low risk populations.

Against this background the following assessment sets out to answer four questions:

Is an elevated homocysteine plasma concentration a strong, consistent and independent (of other classic risk factors) predictor for coronary heart disease?Does a therapeutic lowering of elevated homoysteine plasma levels reduce the risk of developing coronary events?What is the cost-effectiveness relationship of homocysteine testing for preventive purposes?Are there morally, socially or legally relevant aspects that should be considered when implementing a preventive strategy as outlined above?

Methods

In order to answer the first question, a systematic overview of prospective studies and metaanalyses of prospective studies is undertaken. Studies are included that analyse the association of homocysteine plasma levels with future cardiac events in probands without pre-existing coronary heart disease or in population-based samples. To answer the second question, a systematic overview of the literature is prepared, including randomised controlled trials and systematic reviews of randomised controlled trials that determine the effectiveness of homocysteine lowering therapy for the prevention of cardiac events. To answer the third question, economic evaluations of homocysteine testing for preventive purposes are analysed. Methodological quality of all materials is assessed by widely accepted instruments, evidence was summarized qualitatively.

Results

For the first question eleven systematic reviews and 33 single studies (prospective cohort studies and nested case control studies) are available. Among the studies there is profound heterogeneity concercing study populations, classification of exposure (homocysteine measurements, units to express “elevation”), outcome definition and measurement, as well as controlling for confounding (qualitatively and quantitatively). Taking these heterogeneities into consideration, metaanalysis of single patient data with controlling for multiple confounders seems to be the only adequate method of summarizing the results of single studies. The only available analysis of this type shows, that in otherwise healthy people homocysteine plasma levels are only a very weak predictor of future cardiac events. The predictive value of the classical risk factors is much stronger. Among the studies that actively exclude patients with pre-existing coronary heart disease, there are no reports of an association between elevated homocysteine plasma levels and future cardiac events.

Eleven randomized controlled trials (ten of them reported in one systematic review) are analysed in order to answer the second question. All trials include high risk populations for the development of (further) cardiac events. These studies also present with marked clinical heterogeneity: primarily concerning the average homocysteine plasma levels at baseline, type and mode of outcome measurement and as study duration. Except for one, none of the trials shows a risk reduction for cardiac events by lowering homocysteine plasma levels with folate or B vitamins. These results also hold for predefined subgroups with markedly elevated homocysteine plasma levels.

In order to answer the third questions, three economic evaluations (modelling studies) of homocysteine testing are available. All economic models are based on the assumption that lowering homocysteine plasma levels results in risk reduction for cardiac events. Since this assumption is falsified by the results of the interventional studies cited above, there is no evidence left to answer the third question.

Morally, socially or legally relevant aspects of homocysteine assessment are currently not being discussed in the scientific literature.

Discussion and conclusion

Many currently available pieces of evidence contradict a causal role of homocysteine in the pathogenesis of coronary heart disease. Arguing with the Bradford-Hill criteria at least the criterion of time-sequence (that exposure has to happen before the outcome is measured), the criterion of a strong and consistent association and the criterion of reversibility are not fulfilled. Therefore, homocysteine may, if at all, play a role as a risk indicator but not as risk factor.

Furthermore, currently available evidence does not imply that for the prevention of coronary heart disease, knowledge of homocysteine plasma levels provides any information that supersedes the information gathered from the examination of classical risk factors. So, currently for the indication of prevention, there is no evidence that homocysteine testing provides any benefit. Against this background there is also no basis for cost-effectiveness calculations.

Further basic research should clarify the discrepant results of case control studies and prospective studies. Maybe there is a third parameter (confounder) associated with homocysteine metabolism as well with coronary heart disease. Further epidemiological research could elucidate the role of elevated homocysteine plasma levels as a risk indicator or prognostic indicator in patients with pre-existing coronary heart disease taking into consideration the classical risk factors.

The unique biochemical profile of homocysteine is characterized by chemical reactivity supporting a wide range of molecular effects, and a tendency to promote oxidant stress-induced cellular toxicity. Numerous epidemiological reports have established hyperhomocysteinemia as an independent risk factor for cardiovascular disease, cerebrovascular disease, dementia-type disorders, and osteoporosis-associated fractures. Although combined folic acid and B-vitamin therapy substantially reduces homocysteine levels, results from randomized placebo-controlled clinical trials testing the effect of vitamin therapy on outcome in these diseases are mixed, but have generally fallen short of expectations. These results have led some to abandon homocysteine monitoring in the management of patients with cardiovascular or cognitive disorders. These trials, however, have generally included patients with only mildly elevated homocysteine levels, and have not addressed several clinical scenarios in which homocysteine level reduction may be effective, including the primary prevention of atherothrombotic disease in individuals at low- or intermediate-risk, or those with severe hyperhomocysteinemia.

Background:

Vitamin B12 (B12) deficiency is common in Indians and a major contributor to hyperhomocysteinemia, which may influence fetal growth, risk of type 2 diabetes and cardiovascular disease.

Objective:

To study the effect of physiological doses of B12 and folic acid on plasma total homocysteine (tHcy).

Design:

A cluster randomized, placebo-controlled, double-blind, 2x3 factorial trial, using the family as the randomization unit. Vitamin B12 was given as 2 or 10 μg capsules, with or without 200 μg folic acid, forming six groups (B0F0, B2F0, B10F0, B0F200, B2F200, B10F200). Plasma tHcy was measured before and after 4 and 12 mo of supplementation.

Results:

Three hundred individuals from 119 families in the Pune Maternal Nutrition Study were randomised. There was no interaction between B12 and folic acid (P=0.14) in relation to tHcy change and their effects were analyzed separately: B0 vs. B2 vs. B10; and F0 vs. F200. At 12 mo, tHcy fell by a mean 5.9 (95% CI: −7.8, −4.1) μmol/L in B2, and by 7.1 (95% CI: −8.9, −5.4) μmol/L in B10, compared to non-significant rise of 1.2 (95% CI: −0.5, 2.9) μmol/L in B0. B2 and B10 did not differ significantly. In F200, tHcy fell by 4.8 (95% CI: −6.3, −3.3) μmol/L compared to 2.8 (95% CI: −4.3, −1.2) μmol/L in F0.

Conclusion:

Daily oral supplementation with physiological doses of B12 is an effective community intervention to reduce tHcy. Folic acid (200 μg/d) showed no additional benefit, neither had any unfavourable effects.

Homocysteine is a sulfur-containing aminoacid produced during metabolism of methionine. Since 1969 the relationship between altered homocysteine metabolism and both coronary and peripheral atherotrombosis is known; in recent years experimental evidences have shown that elevated plasma levels of homocysteine are associated with an increased risk of atherosclerosis and cardiovascular ischemic events. Several mechanisms by which elevated homocysteine impairs vascular function have been proposed, including impairment of endothelial function, production of reactive oxygen species (ROS) and consequent oxidation of low-density lipids. Endothelial function is altered in subjects with hyperhomocysteinemia, and endothelial dysfunction is correlated with plasma levels of homocysteine. Folic acid and B vitamins, required for remethylation of homocysteine to methionine, are the most important dietary determinants of homocysteine and daily supplementation typically lowers plasma homocysteine levels; it is still unclear whether the decreased plasma levels of homocysteine through diet or drugs may be paralleled by a reduction in cardiovascular risk.

Background and Purpose

Although lower serum homocysteine concentration is associated with a reduced risk of stroke in epidemiologic studies, randomized controlled trials (RCTs) have yielded mixed findings regarding the effect of therapeutic homocysteine lowering on stroke prevention. We performed a meta-analysis of RCTs to assess the efficacy of folic acid supplementation in the prevention of stroke.

Methods

Salient trials were identified by formal literature search. Relative risk (RR) with 95% confidence interval (CI) was used as a measure of the association between folic acid supplementation and risk of stroke, pooling data across trials using a fixed-effects model.

Results

The search identified 13 RCTs of folic acid therapy to reduce homocysteine, enrolling 39,005 participants, in which stroke was reported as an outcome measure. Across all trials, folic acid supplementation was associated with a trend toward mild benefit that did not reach statistical significance in reducing the risk of stroke (RR 0.93, 95% CI 0.85-1.03; p=0.16). The RR for non-secondary prevention trials was 0.89 (95% CI 0.79-0.99; p=0.03). In stratified analyses, a greater beneficial effect was seen in the trials testing combination therapy of folic acid plus vitamins B6 and B12 (RR 0.83, 0.71-0.97; p=0.02) and in the trials which disproportionately enrolled male patients (men/women > 2, RR 0.84, 0.74-0.94; p=0.003).

Conclusions

Folic acid supplementation did not demonstrate a major effect in averting stroke. However, potential mild benefits in primary stroke prevention, especially when folate is combined with B vitamins and in male patients, merit further investigation.

Context

Folate, vitamin B6, and vitamin B12 are thought to play an important role in cancer prevention.

Objective

To evaluate the effect of combined folic acid, vitamin B6, and vitamin B12 treatment on cancer risk in women at high risk for cardiovascular disease.

Design, Setting, and Participants

In the Women’s Antioxidant and Folic Acid Cardiovascular Study, 5442 US female health professionals aged 42 years or older with preexisting cardiovascular disease or 3 or more coronary risk factors were randomly assigned to receive either a daily combination of folic acid, vitamin B6, and vitamin B12 or placebo in April 1998, and treated through July 31, 2005 for 7.3 years.

Intervention

Daily supplementation of a combination of 2.5 mg of folic acid, 50 mg of vitamin B6, and 1 mg of vitamin B12 (n=2721) or placebo (n=2721).

Main Outcome Measures

Confirmed newly diagnosed total invasive cancer.

Results

A total of 379 women developed invasive cancer (187 in the active group and 192 in the placebo group). Compared with placebo, women receiving combined folic acid, vitamin B6, and vitamin B12 had similar risk of developing total invasive cancer (101.1/10000 person-years vs 104.3/10000 person-years for the active vs placebo group; hazard ratio, 0.97; 95% confidence interval, 0.79–1.18; P=.75), breast cancer (37.8/10000 person-years vs 45.6/10000 person-years; hazard ratio, 0.83; 95% confidence interval, 0.60–1.14; P=.24), and any cancer death (24.6/10000 person-years vs 30.1/10000 person-years; hazard ratio, 0.82; 95% confidence interval, 0.56–1.21; P=.32).

Conclusions

Combined folic acid, vitamin B6, and vitamin B12 treatment had no significant effect on overall risk of total invasive cancer or breast cancer among women during folic acid fortification era.

Trial Registration

clinicaltrials.gov Identifier: NCT00000541

Aims/hypothesis

There is evidence that plasma homocysteine augments vein graft failure and that it augments both micro- and macro-angiopathy in patients with diabetes mellitus. It is therefore suggested that homocysteine may augment vein graft thickening, a major cause of vein graft failure, in diabetic patients, as well as impairing adaptive growth of a new vasa vasorum, possibly through overproduction of superoxide. In order to test these proposals, the effect of folic acid administration, which lowers plasma homocysteine, on vein graft thickening and microvessel density was studied in pigs used as a model of diabetes.

Methods

Non-ketotic hyperglycaemia was induced in Landrace pigs by intravenous injection of streptozotocin, and folic acid was fed daily for 1 month. Vein grafts were excised and the thickness of the neointima and media and microvessel density were assessed by planimetry and superoxide formation.

Results

Plasma total homocysteine was significantly reduced by folic acid in both control and diabetic pigs, whereas glucose was unchanged. Compared with controls, diabetic pigs showed increased neointimal thickness and superoxide formation and decreased adventitial microvessel density. Folic acid reduced neointimal thickness and superoxide formation and augmented microvessel density in diabetic but not in control pigs.

Conclusions

Folic acid administration reduces neointimal thickening, augments vasa vasorum neoformation and reduces oxidative stress in saphenous vein grafts from diabetic pigs. Folic acid may therefore be particularly effective in reducing vein graft failure in diabetic patients.

Homocysteine(Hcy) has been implicated as a novel risk factor of Coronary Artery Disease (CAD) among Asian Indians, but many studies done in India failed to reveal any direct correlation. It has also been reported that Folic acid and Vitamin B12 levels inversely affect serum levels of homocysteine. In this study, we looked at the levels of homocysteine among patients with CAD. The effect of Vitamin B12, Folate and other risk factors on homocysteine levels were also evaluated. Mean homocysteine levels in cases (22.81±13.9, n=70) were significantly higher (p=<0.001) than the controls (7.77±7.3, n=70). However no statistically significant correlation could be deduced between homocysteine Vitamin B12, and Folate. Cumulative analysis have indicated an increase in homocysteine levels among patients with CAD with every additional risk factor.

Background

Patients suffering from malignancies have increased complications due to corresponding cardiovascular diseases and risk factor for the development of venous thromboembolism. Epidemiological studies have shown that increased homocysteine plasma concentration (hyperhomocysteinemia) is related to a higher risk of coronary heart disease, stroke, peripheral vascular disease and malignancies. Homocysteine (tHcy) is an intermediate sulfur-containing amino acid produced from methionine during processing of dietary proteins. The plasma homocysteine levels are strongly influenced by diet, as well as by genetic factors. Folic acid, vitamins B6 and B12 are dietary components which influence the plasma homocysteine levels the most. Several studies have found that high blood levels of B vitamins are related to the integrity and function of DNA, and, are at least related to lower concentration of homocysteine. Folate depletion has been found to change DNA methylation and DNA synthesis in both animal and human studies. Because of this critical role of folate, most studies including homocysteine have focused on these two actions.

Conclusions

Hyperhomocysteinemia proves to be the most common condition highly associated with both venous and arterial thrombosis in many cancer patients, while the associated pathophysiology has not been precisely established yet. Therefore, of current interest is the possible role of folate metabolism developing into a cancer initiating hyperhomocysteinemia. This review will discuss this possibility.

DEMENTIA IS HIGHLY PREVALENT AMONG ELDERLY PEOPLE, and projections show that the number of people affected might triple over the next 50 years, mainly because of a large increase in the oldest-old segment of the population. Because of this and the disease's devastating effects, measures for the prevention and early detection of dementia are crucial. Age and years of education are among the most relevant risk factors for dementia, but in recent years the role of homocysteine has also been investigated. Homocysteine is an amino acid produced in the metabolism of methionine, a process dependent on the B vitamins cobalamin, vitamin B6 and folic acid. There is evidence that increased serum homocysteine levels are associated with declining cognitive function and dementia. We review this evidence in addition to the potential mechanisms through which homocysteine acts on the brain to cause cognitive dysfunction, the metabolism of homocysteine and factors associated with alteration of the normal metabolism.

Background

Hyperhomocysteinemia may be a modifiable risk factor for the prevention of arteriosclerotic outcomes in chronic kidney disease (CKD). Few clinical trials of homocysteine lowering have been conducted in persons with CKD prior to reaching end-stage renal disease. Kidney transplant recipients are considered individuals with CKD.

Objectives

To describe the baseline characteristics of renal transplant recipients (RTRs) enrolled in a clinical trial of homocyteine lowering with a standard multivitamin containing high doses of folic acid, vitamins B6 and B12 aimed at reducing arteriosclerotic outcomes. Factors considered were level of kidney function, total homocysteine (tHcy) concentrations, and the prevalence of diabetes and previous cardiovascular disease (CVD).

Study Design

Cross sectional survey within a randomized controlled trial (RCT) cohort.

Setting and Participants

Participants were recruited from kidney transplant clinics in the U.S., Canada, and Brazil. Eligible participants had elevated levels of homocysteine (≥12.0 μmol/L in men and ≥11.0 μmol/L in women) and kidney function measured by Cockroft Gault estimated creatinine clearance of 30 mL/min or greater.

Results

Among 4,110 randomized participants 38.9% had diabetes, and 19.5% had previous CVD. Mean (± standard deviation) tHcy concentrations were 17.1 ± 6.3 μmol/L, while the mean (± standard deviation) creatinine clearance was 66.4 ± 23.2 mL/min. Approximately 90% of the trial cohort had an estimated glomerular filtration rate (eGFR) consistent with stage 2-3 CKD (i.e., eGFR 30-89 mL/min).

Limitations

Analysis is based on cross-sectional data from a RCT, self-report of co-morbid illnesses, and level of kidney function was estimated.

Conclusions

A large population of stable RTRs who are at high risk for the development of CVD (both de novo and recurrent) has been recruited into FAVORIT and are likely to experience a sufficient number of events to address the primary hypothesis of the trial.

The present study was carried out to evaluate the occurrence of association between homocysteine, folic acid and vitamin B12 in patients with preeclampsia. Fifty preeclamptic patients from gynecology ward were studied for estimation of serum homocysteine, folic acid and vitamin B12 over a period of October 2007 to June 2010. Serum homocysteine and folic acid, and vitamin B12 were determined by means of Immulite 1000 analyzer. The statistical analysis of study group of preeclampsia compared with normotensive control group, showed significant alterations in serum homocysteine, folic acid and vitamin B12 concentrations in preeclampsia. Inverse association between serum homocysteine and folic acid, and vitamin B12 levels were observed in preeclampsia. The present study found hyperhomocysteinemia and deficiency of folic acid and vitamin B12 along with increased blood pressure as a risk factor for cardiovascular disease (CVD) in preeclampsia.

OBJECTIVE

To review recent evidence that suggests vitamin B12 is associated with risk reduction for some chronic diseases and birth defects.

QUALITY OF EVIDENCE

A MEDLINE search from 1999 to 2007 was performed using the key word vitamin B12. The most relevant articles (129) dealt with cardiovascular disease, cancer, mental health, and birth outcomes; most studies presented level II evidence.

MAIN MESSAGE

Vitamin B12 might confer health benefits; however, such benefits are difficult to ascertain because of the complementary functions of vitamin B12 and folic acid. Vitamin B12 might lower high homocysteine levels below a threshold level achieved by folic acid alone. Furthermore, the interactions between the nutritional environment and genotype might have an important influence on vitamin B12, chronic disease risk, and risk of neural tube defects.

CONCLUSION

Vitamin B12 might help protect against chronic disease and neural tube defects, but more research, particularly in the area of nutritional genomics, is needed to determine how vitamin B12 might augment the benefits of folic acid. Some consideration should be given to the potential value of fortifying foods with vitamin B12 in addition to the current mandatory folic acid fortification of grains.

Objectives:

We investigated whether lowering of fasting homocysteine concentrations, either with folic acid or with betaine supplementation, differentially affects vascular function, a surrogate marker for risk of cardiovascular disease, in healthy volunteers. As yet, it remains uncertain whether a high concentration of homocysteine itself or whether a low folate status—its main determinant—is involved in the pathogenesis of cardiovascular disease. To shed light on this issue, we performed this study.

Design:

This was a randomized, placebo-controlled, double-blind, crossover study.

Setting:

The study was performed at Wageningen University in Wageningen, the Netherlands.

Participants:

Participants were 39 apparently healthy men and women, aged 50–70 y.

Interventions:

Participants ingested 0.8 mg/d of folic acid, 6 g/d of betaine, and placebo for 6 wk each, with 6-wk washout in between.

Outcome Measures:

At the end of each supplementation period, plasma homocysteine concentrations and flow-mediated dilation (FMD) of the brachial artery were measured in duplicate.

Results:

Folic acid supplementation lowered fasting homocysteine by 20% (−2.0 μmol/l, 95% confidence interval [CI]: −2.3; −1.6), and betaine supplementation lowered fasting plasma homocysteine by 12% (−1.2 μmol/l; −1.6; −0.8) relative to placebo. Mean (± SD) FMD after placebo supplementation was 2.8 (± 1.8) FMD%. Supplementation with betaine or folic acid did not affect FMD relative to placebo; differences relative to placebo were −0.4 FMD% (95%CI, −1.2; 0.4) and −0.1 FMD% (−0.9; 0.7), respectively.

Conclusions:

Folic acid and betaine supplementation both did not improve vascular function in healthy volunteers, despite evident homocysteine lowering. This is in agreement with other studies in healthy participants, the majority of which also fail to find improved vascular function upon folic acid treatment. However, homocysteine or folate might of course affect cardiovascular disease risk through other mechanisms.

Editorial Commentary

Background: Evidence from observational studies indicates a link between high concentrations of homocysteine (an amino acid) in the blood and increased risk of cardiovascular disease. However, the basis for the link between homocysteine concentrations and cardiovascular disease risk is not clear. Supplementing the diet with B-vitamins lowers homocysteine levels, and large-scale trials are underway that will determine whether B-vitamin supplementation has an effect on cardiovascular outcomes, such as heart attacks and strokes. These trials also involve administration of folic acid as well as other B-vitamins. It is not obvious, however, whether the effects of B-vitamin supplementation arise as a result of homocysteine lowering or via some other biochemical pathway.

What this trial shows: Olthof and colleagues aimed to further understand the effects of homocysteine lowering by randomizing 40 healthy volunteer participants to receive either folic acid supplementation; placebo; or betaine, a nutrient that lowers homocysteine levels via a different biochemical pathway than folic acid. Each participant in the trial received each supplement for 6 wk, with a 6-wk washout period before the next supplement was given. The researchers then used a technique called flow-mediated dilation (FMD) to measure functioning of the main artery of the upper arm, as a surrogate for cardiovascular disease risk. In this trial, both folic acid and betaine supplementation significantly lowered homocysteine levels over the 6-wk supplementation period. However, both forms of supplementation failed to result in any significant change in functioning of the artery, as measured using FMD.

Strengths and limitations: In this trial 40 participants were recruited, and 39 were followed up to trial completion. A crossover design was used, with each participant receiving each supplement and a placebo in sequence. This method enabled a smaller number of participants to be used to answer the question of interest, as compared to parallel-group designs. The majority of participants in the trial were followed up. However, the trial's outcomes are surrogates for cardiovascular disease risk, measured over fairly short time periods, and no clinical outcomes were examined.

Contribution to the evidence: This trial adds to the evidence on the effects of nutrient supplementation on surrogate outcomes for cardiovascular disease risk. The results show that over a 6-wk study period, these surrogate outcomes are not affected by either folic acid or betaine supplementation.

Background

An increased rate of brain atrophy is often observed in older subjects, in particular those who suffer from cognitive decline. Homocysteine is a risk factor for brain atrophy, cognitive impairment and dementia. Plasma concentrations of homocysteine can be lowered by dietary administration of B vitamins.

Objective

To determine whether supplementation with B vitamins that lower levels of plasma total homocysteine can slow the rate of brain atrophy in subjects with mild cognitive impairment in a randomised controlled trial (VITACOG, ISRCTN 94410159).

Methods and Findings

Single-center, randomized, double-blind controlled trial of high-dose folic acid, vitamins B6 and B12 in 271 individuals (of 646 screened) over 70 y old with mild cognitive impairment. A subset (187) volunteered to have cranial MRI scans at the start and finish of the study. Participants were randomly assigned to two groups of equal size, one treated with folic acid (0.8 mg/d), vitamin B12 (0.5 mg/d) and vitamin B6 (20 mg/d), the other with placebo; treatment was for 24 months. The main outcome measure was the change in the rate of atrophy of the whole brain assessed by serial volumetric MRI scans.

Results

A total of 168 participants (85 in active treatment group; 83 receiving placebo) completed the MRI section of the trial. The mean rate of brain atrophy per year was 0.76% [95% CI, 0.63–0.90] in the active treatment group and 1.08% [0.94–1.22] in the placebo group (P = 0.001). The treatment response was related to baseline homocysteine levels: the rate of atrophy in participants with homocysteine >13 µmol/L was 53% lower in the active treatment group (P = 0.001). A greater rate of atrophy was associated with a lower final cognitive test scores. There was no difference in serious adverse events according to treatment category.

Conclusions and Significance

The accelerated rate of brain atrophy in elderly with mild cognitive impairment can be slowed by treatment with homocysteine-lowering B vitamins. Sixteen percent of those over 70 y old have mild cognitive impairment and half of these develop Alzheimer's disease. Since accelerated brain atrophy is a characteristic of subjects with mild cognitive impairment who convert to Alzheimer's disease, trials are needed to see if the same treatment will delay the development of Alzheimer's disease.

Trial Registration

Controlled-Trials.com ISRCTN94410159

There is a significant fall in the serum folic acid level during pregnancy, reaching its lowest level at term. This is most pronounced in twin pregnancies. A similar but less spectacular fall occurs in the vitamin B12 concentration.

In megaloblastic anaemia both folic acid and vitamin B12 levels are lower than in other pregnant women. The degree of megaloblastic change in the bone marrow, as measured by the type and number of megaloblasts, is reflected in the vitamin levels, cases with florid megaloblastosis showing the most marked depression of vitamin B12 and folic acid activity.

Although there is a significant difference in the mean folic acid levels between megaloblastic and normoblastic pregnant women, a considerable overlap exists between individual values in the two groups. When the labile folic-acid factor is determined separately the test becomes much more specific. In the present series, all cases of megaloblastic anaemia yielded labile-factor levels below 1·0 mμg. per ml., while a similar value was encountered in only one of 35 normal pregnancies.

In five women with megaloblastic anaemia the vitamin B12 concentration was less than 100 μμg. per ml. but rose to normal levels on folic acid therapy alone.

Images