VISP Trial Analysis Says High-Dose B Vitamin Mix Lowers Stroke Risk

High doses of a combined B vitamin therapy yielded a 21% reduction in risk of stroke and other negative outcomes compared to low doses, an "efficacy analysis" of the VISP trial found.

Patients with baseline levels of B12 at the median or higher who were then randomized to the high-dose arm had the best overall outcome for the combined end point of ischemic stroke, coronary disease or death, the authors report in the November issue of Stroke.

David Spence, MD, Robarts Research Institute, Ontario, Canada, et al., revisited data from their Vitamin Intervention for Stroke Prevention Trial (VISP), which was published in February 2004 in the Journal of the American Medical Association.

VISP involved 3,680 subjects who had experienced ischemic stroke at 56 sites in the U.S., Canada and Scotland. Patients were randomized to either high-dose or low-dose vitamin supplements. The high-dose formulation contained 25 mg vitamin B6, 0.4 mg B12 and 2.5 mg folic acid.

The original study found no significant reduction of stroke risk in the high-dose arm.

However, Spence et al. 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."

For the analysis, the authors excluded patients who had low or very high B12 levels at baseline to rule out subjects with B12 malabsorption or renal impairment and those taking supplements outside the study.

The resulting subgroup of 2,155 patients was 37% female, with a mean age of 66 years.

The reduced stroke risk is due primarily to reduced levels of serum homocysteine.

The results demonstrate that vitamin B12 "plays a key role in vitamin therapy for total homocysteine," the authors conclude. "Higher doses of B12 and other treatments to lower total homocysteine may be needed for some patients."

- Christopher Walker