Homocysteine-lowering trials for prevention of cardiovascular events: a review of the design and power of the large randomized trials.

BACKGROUND: Dietary supplementation with folic acid and vitamin B12 lowers blood homocysteine concentrations by about 25% to 30% in populations without routine folic acid fortification of food and by about 10% to 15% in populations with such fortification. In observational studies, 25% lower homocysteine has been associated with about 10% less coronary heart disease (CHD) and about 20% less stroke. METHODS: We reviewed the design and statistical power of 12 randomized trials assessing the effects of lowering homocysteine with B-vitamin supplements on risk of cardiovascular disease. RESULTS: Seven of these trials are being conducted in populations without fortification (5 involving participants with prior CHD and 2 with prior stroke) and 5 in populations with fortification (2 with prior CHD, 2 with renal disease, and 1 with prior stroke). These trials may not involve sufficient number of vascular events or last long enough to have a good chance on their own to detect reliably plausible effects of homocysteine lowering on cardiovascular risk. But, taken together, these 12 trials involve about 52,000 participants: 32,000 with prior vascular disease in unfortified populations and 14,000 with vascular disease and 6000 with renal disease in fortified populations. Hence, a combined analysis of these trials should have adequate power to determine whether lowering homocysteine reduces the risk of cardiovascular events within just a few years. CONCLUSION: The strength of association of homocysteine with risk of cardiovascular disease may be weaker than had previously been believed. Extending the duration of treatment in these trials would allow any effects associated with prolonged differences in homocysteine concentrations to emerge. Establishing a prospective meta-analysis of the ongoing trials of homocysteine lowering should ensure that reliable information emerges about the effects of such interventions on cardiovascular disease outcomes

VITATOPS, the VITAmins TO Prevent Stroke Trial: Rationale and design of a randomised trial of B-vitamin therapy in patients with recent transient ischaemic attack or stroke (NCT00097669) (ISRCTN74743444)

Background Epidemiological studies suggest that raised plasma concentrations of total homocysteine (tHcy) may be a common, causal and treatable risk factor for atherothromboembolic ischaemic stroke, dementia and depression. Although tHcy can be lowered effectively with small doses of folic acid, vitamin B12 and vitamin B6, it is not known whether lowering tHcy, by means of B vitamin therapy, can prevent stroke and other major atherothromboembolic vascular events. Aim To determine whether the addition of B-vitamin supplements (folic acid 2 mg, B6 25 mg, B12 500 μg) to best medical and surgical management will reduce the combined incidence of stroke, myocardial infarction (MI) and vascular death in patients with recent stroke or transient ischaemic attack (TIA) of the brain or eye. Design A prospective, international, multicentre, randomised, double blind, placebo-controlled clinical trial. Setting One hundred and four medical centres in 20 countries on five continents. Subjects Eight thousand (6600 recruited as of 5 January, 2006) patients with recent (7 months) stroke (ischaemic or haemorrhagic) or TIA (brain or eye). Randomisation Randomisation and data collection are performed by means of a central telephone service or secure internet site. Intervention One tablet daily of either placebo or B vitamins (folic acid 2mg, B6 25 mg, B12 500 μg). Primary outcome The composite of stroke, MI or death from any vascular cause, whichever occurs first. Outcome and serious adverse events are adjudicated blinded to treatment allocation. Secondary outcomes TIA, unstable angina, revascularisation procedures, dementia, depression. Statistical power With 8000 patients followed up for a median of 2 years and an annual incidence of the primary outcome of 8% among patients assigned placebo, the study will have at least 80% power to detect a relative reduction of 15% in the incidence of the primary outcome among patients assigned B vitamins (to 6·8%/year), applying a two-tailed level of significance of 5%. Conclusion VITATOPS aims to recruit and follow-up 8000 patients between 1998 and 2008, and provide a reliable estimate of the safety and effectiveness of folic acid, vitamin B12, and vitamin B6 supplementation in reducing recurrent serious vascular events among a wide range of patients with TIA and stroke throughout the world. The VITATOPS Trial Study Grou

Effects of folic acid supplementation on overall and site-specific cancer incidence during the randomised trials: meta-analyses of data on 50,000 individuals.

Some countries fortify flour with folic acid to prevent neural tube defects but others do not, partly because of concerns about possible cancer risks. We aimed to assess any effects on site-specific cancer rates in the randomised trials of folic acid supplementation, at doses higher than those from fortification

Relationship between two sequence variations in the gene for peroxisome proliferator-activated receptor-gamma and plasma homocysteine concentration. Health in men study

The concentration of circulating homocysteine has been associated with a variety of diseases, including myocardial infarction, stroke, venous thrombosis and cognitive decline. Genetic variation has been demonstrated to play an important role in determining plasma homocysteine, however, the genes involved are incompletely understood. Ligation of the transcription factor peroxisome proliferator-activated gamma (PPARG) has been demonstrated to lower plasma homocysteine. We examined the association of two sequence variations in PPARG with plasma concentrations of homocysteine in a population-based study of 3,875 elderly men. PPARG c.34G > C and PPARG c.1347C > T sequence variations were determined by real-time quantitative PCR and related to logarithm transformed homocysteine concentrations using linear regression, adjusting for the co-variants age, renal function, smoking, coronary heart disease, waist to hip ratio, diabetes, hypertension and MTHFR g.677C > T sequence variation. Median plasma homocysteine concentration was 10% higher in men who were homozygous for the rare allelic variation in PPARG c.34G > C and PPARG c.1347C > T by comparison to those who had wild type sequence variation. PPARG c.1347C > T (β = 0.038, P = 0.01 recessive model; β = 0.036, P = 0.02 dominant model) sequence variation was positively associated with homocysteine concentration after adjusting for co-variants. The two PPARG sequence variations were in linkage disequilibrium and the common haplotype was associated with lower plasma homocysteine (P = 0.005). Our findings demonstrate a new genotypic association with plasma homocysteine. Replication will be required in other cohorts

Homocysteine, B Vitamins, and Cardiovascular Risk

Several observational studies have associated homocysteine with atherosclerotic disease. B vitamins, and particularly folic acid, B12 and B6, reduce homocysteine levels effectively. Hence, it was suggested that B vitamin supplementation could reduce cardiovascular risk. However, the results of several randomized clinical trials have not confirmed this hypothesis. This chapter presents the association of homocysteine and B vitamins with cardiovascular risk, and discusses the available data. © 2015 Elsevier Inc. All rights reserved