Vitamin Intervention for Stroke Prevention Trial

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Abstract
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 (637 pmol/L, rep...