It isn't strong enough evidence to justify a change in public health policy

Professor John Mathers, University of Newcastle

Blood tests suggested that all 29, while apparently completely healthy, had elevated levels of a chemical called homocysteine.

This has already been linked with hardening of the arteries, which can cause heart disease.

After a year of extra folic acid, all 29 had their homocysteine levels re-tested.

In addition, doctors used ultrasound to check how well their blood vessel walls were working, using ultrasound.

It is believed that artery hardening happens partly because the walls lose elasticity, robbing it of the ability to widen when necessary.

They found that homocysteine levels had fallen by 12%, and that the artery walls appeared to work more efficiently.

Testing process

Dr Irwin Rosenberg, of the Human Nutrition Research Center at Tufts University, Boston, suggested that future heart disease screening tests could concentrate on homocysteine levels.

He said: "Is it time or even past time for the modification of the diet-heart hypothesis, which has for decades focused on the levels of dietary fat, cholesterol, and, with less evidence, dietary salt?

"We should, I believe, begin to standardise the quality and reproducibility of the tests of blood homocysteine offered in the clinical setting."

However, UK experts are cautious about using the latest results as a justification for universal folic acid fortification.

Professor John Mathers, from the University of Newcastle, said: "It's an interesting study but really just another piece of the puzzle.

"It isn't strong enough evidence to justify a change in public health policy."