Giving B vitamins to Heart Attack survivors does not cut their risk of having another attack and may actually do more harm than good, researchers said on Monday.

The finding confounds supporters of vitamins, including some doctors, who have argued that folic acid and Vitamin B6 can prevent Heart disease by reducing levels of a substance called homocysteine in the blood.

A study of more than 3,700 patients presented at the European Society of Cardiology congress showed high doses of B vitamins could be bad news.

Those who took folic acid or vitamin B-6 alone had a small and statistically insignificant increase in the risk of cardiovascular disease, but those who took both saw their risk jump by 20 percent.

Professor Kaare Harald Bonaa of the University of Tromso, Norway, said the 3-year trial showed vitamins did reduce homocysteine levels, by around 30 percent, but this did not translate into lowered heart risk.

“The homocysteine hypothesis is dead,” he told reporters.

Homocysteine, an amino acid, is produced when the body metabolises high-protein foods. Scientists think that high concentrations could damage blood-vessel walls.

“The results of the trial are important because they tell doctors that prescribing high doses of B vitamins will not prevent Heart disease or Stroke. B vitamins should be prescribed only to patients who have B vitamin deficiency,” Bonaa said.