Study leader Dr. Marta Ebbing of Haukeland University Hospital in Bergen, Norway, said 3,096 patients with coronary artery disease between 1999 to 2006 were randomly assigned to one of four groups that received a daily oral dose of one of the following treatments: folic acid, vitamin B12 plus vitamin B6, folic acid plus vitamin B12, vitamin B6 alone or placebo.

The researchers said they could not detect any preventive effect of intervention with folic acid plus vitamin B12 or with vitamin B6 on mortality or major cardiovascular events among the patients.

"Observational studies have demonstrated that the concentration of total homocysteine in blood is associated with risk of coronary artery disease and stroke," the authors said in a statement.

"We found a numerically lower incidence of stroke and higher incidence of cancer in the groups receiving folic acid, but these observations were not statistically significant, but the findings do not support the use of B vitamins as secondary prevention in patients with coronary artery disease.

The study was published in the Journal of the American Medical Association.