Published Online
on October 20, 2005

A more recent version of this article appeared on November 1, 2005

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Submitted on July 29, 2005
Accepted on August 15, 2005

Vitamin Intervention for Stroke Prevention Trial. An Efficacy Analysis

J. David Spence MD, FRCPC, FAHA^*; Heejung Bang PhD; Lloyd E. Chambless PhD; and Meir J. Stampfer MD, DrPH

From the Stroke Prevention and Atherosclerosis Research Centre (J.D.S.), Robarts Research Institute, London, Ontario, Canada; VISP Statistical Coordinating Center (H.B., L.E.C.), Department of Biostatistics, University of North Carolina, Chapel Hill; and Departments of Epidemiology and Nutrition (M.J.S.), Harvard School of Public Health, Boston, Mass.

^* To whom correspondence should be addressed. E-mail: dspence{at}robarts.ca.

Background and Purpose--The Vitamin Intervention for Stroke Prevention trial (VISP) intention-to-treat analysis did not show efficacy of combined vitamin therapy for recurrent vascular events in patients with nondisabling stroke. Reasons for lack of efficacy may have included folate fortification of grain products, inclusion of the recommended daily intake for B₁₂ in the low-dose arm, treatment with parenteral B₁₂ in patients with low B₁₂ levels in both study arms, a dose of B₁₂ too low for patients with malabsorption, supplementation with nonstudy vitamins, and failure of patients with significant renal impairment to respond to vitamin therapy. We conducted an efficacy analysis limited to patients most likely to benefit from the treatment, based on hypotheses arising from evidence developed since VISP was initiated. The criteria for this subgroup were defined before any data analysis.

Methods--For this analysis, we excluded patients with low and very high B₁₂ levels at baseline (<250 and >637 pmol/L, representing the 25th and 95th percentiles), to exclude those likely to have B₁₂ malabsorption or to be taking B₁₂ supplements outside the study and patients with significant renal impairment (glomerular filtration rate <46.18; the 10th percentile).

Results--This subgroup represents 2155 patients (37% female), with a mean age of 66±10.7 years. For the combined end point of ischemic stroke, coronary disease, or death, there was a 21% reduction in the risk of events in the high-dose group compared with the low-dose group (unadjusted P=0.049; adjusted for age, sex, blood pressure, smoking, and B₁₂ level P=0.056). In Kaplan-Meier survival analysis comparing 4 groups, patients with a baseline B₁₂ level at the median or higher randomized to high-dose vitamin had the best overall outcome, and those with B₁₂ less than the median assigned to low-dose vitamin had the worst (P=0.02 for combined stroke, death, and coronary events; P=0.03 for stroke and coronary events).

Conclusions--In the era of folate fortification, B₁₂ plays a key role in vitamin therapy for total homocysteine. Higher doses of B₁₂, and other treatments to lower total homocysteine may be needed for some patients.

Key words: homocysteine • stroke prevention • stroke • vitamins

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