The B vitamin group, including folic acid, B6, and B12, reduce the amount of the amino acid homocysteine in the blood. High levels of this substance have been linked to heart disease.
But a previous study by the Vitamin Intervention for Stroke Prevention (VISP) group based in Canada and the US suggested that taking a combination of B9, B6 and B12 did not reduce recurrent stroke and cardiac events.
However work carried out since then suggested to the team that their initial trial included patients who were not likely to benefit from the treatment.
In a new analysis they excluded patients with low and very high B12 levels at baseline. These were likely to have B12 malabsorption or to be taking B12 supplements outside the study. Patients with significant renal impairment were also excluded as they were unlikely to respond to vitamin therapy.
In the remaining 2155 patients, high-dose vitamin supplements reduced recurrent stroke, death and heart disease by 21 per cent compared with those taking low-dose vitamins, they report in the 1 November issue of Stroke Stroke (vol 36, p2404).
When they subdivided patients by baseline levels of vitamin B12, thus identifying those with difficulties absorbing the vitamin, the differences between the low-dose and high-dose groups became greater.
The authors suggest that given the fortification of flour with folate, the response to vitamin therapy for lowering homocysteine largely depends on B12 levels of heart patients.
Higher doses of B12 could be required to reduce homocysteine, and thus to reduce stroke and heart attack.