The UK's Medical Research Council has awarded £280,000 (€403, 000) to fund the UK arm of the Vitatops study that will see up to 1,000 stroke patients recruited from the UK.
The trial aims to gather 8000 patients by the end of the year. The patients will be randomised in a double-blind study to receive either supplements including vitamin B12, B6 and folic acid or a placebo daily for five years.
Recent research has suggested that raised levels of homocysteine in the blood may be a treatable cause of the most common types of stroke. Small doses of B vitamins have been shown to lower these raised homocysteine levels.
If the study shows that vitamin supplements are effective, they will be a safe and inexpensive treatment that can be given to virtually every patient at risk of stroke.
First-time stroke afflicts some 100,000 people every year in the UK. People who have already had a stroke are more likely than average to have another.
Conventional treatments to prevent further strokes are targeted at lowering blood pressure and include aspirin and cholesterol-lowering drugs. For some patients, however, these drugs are not cost-effective and for others their side-effects make them unsuitable.
The UK's coordinator Professor Kennedy Lees, from the university of Glasgow's Department of Medicine and Therapeutics, said: "Stroke is the main cause of disability and one of the main causes of death in the UK. Affecting young people as well as the elderly, stroke remains a substantial burden for the patient, carers and society."
"This study is one of major public health importance as the findings will have the potential to benefit the lives of thousands and to reduce costs to an already over-burdened NHS [National Health Service]."
The study should help to clarify the role of supplements in heart health. Numerous studies have investigated whether folic acid can prevent heart attacks but so far results have been inconclusive.
Other countries participating in the trial include Australia, Austria, Brazil, Italy, Malaysia, New Zealand, Philippines, Portugal, Republic of Georgia, Singapore, Sri Lanka, US and Yugoslavia.