Experts warn: regular taking B vitamins to prevent heart attacks and stroke may even be harmful.
Scientists had thought that these drugs might be useful by lowering levels of a blood substance called homocysteine which has been linked heart risk.
However, a new study looking at this has found no benefit even though homocysteine went down with these supplement pills.
The work was revealed in Stockholm at a European Society of Cardiology meeting.
The Norwegian Vitamin Trial (NORVIT) researchers looked at 4,749 heart attack survivors who had been divided into four groups.
In addition to their standard heart medicines, the groups received either daily (itself a B vitamin), daily vitamin B6, both folic acid and vitamin B6 or a dummy drug for three years.
After three and a half years, those who had been taking either folic acid or vitamin B6 alone had only a small increase in the risk of cardiovascular disease (heart attack or stroke), compared with those who had received the placebo.
However, those who had taken both folic acid and vitamin B6 each day had a 20% increased risk of heart attack and stroke.
According to the AP the results also showed there was a 40% increase in the risk of new cancers in the group taking folic acid, which the researchers said warranted further investigation.