The American Heart Association recommends fruits and vegetables containing the B vitamins
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• 'We don't have definitive proof'
• A 'modest' risk factor
• A whole new domain of markers
• Related sites and stories

DALLAS (CNN) -- Fresh fruits and vegetables, rather than vitamin supplements, are the best line of defense against a possible indicator of heart disease, the American Heart Association said Tuesday.

High levels of a blood substance called homocysteine may be linked with the risk of heart disease, and three vitamins -- folic acid, B-6 and B-12 -- may lower homocysteine levels.

The AHA waded cautiously into the scientific debate over the connection between homocysteine and heart disease in a report released at its annual conference.

Some researchers argue that homocysteine is an underappreciated cause of heart trouble that should be brought under control. Others believe it is insignificant.

The AHA compromised by recommending that people eat vitamin-rich food that lowers homocysteine levels, while stopping short of urging special efforts to monitor homocysteine or bring it down with vitamin pills.

"We have to be cautious in assuming that homocysteine is definitely a risk factor for heart disease. We don't have definitive proof," said Dr. Daniel Rader of the University of Pennsylvania.

Dr. Ronald Krauss of the Lawrence Berkeley National Laboratory in Berkeley, California, and colleagues on the AHA's nutrition committee studied results from several trials that looked at the links between homocysteine and heart disease.

He said only six out of 11 trials showed a clear association between high levels of homocysteine and heart disease.

"Until there is proof, rather than emphasizing supplements, we should recommend an increased intake of vegetables, fruits, legumes and fortified grains," Krauss said.

Two more new studies were presented at this week's AHA conference. Both add to the evidence that high homocysteine may be bad, even in those who have no other risks of heart trouble, such as high cholesterol or diabetes.

"Homocysteine appears to be a modest risk factor limited to those with the highest levels," said Dr. Paul Ridker of the Veterans Administration Medical Center and Brigham and Women's Hospital, both in Boston.

A blood test for homocysteine is expensive -- between $50 and $100 -- so at this point there is no justification in telling doctors to test patients routinely for the compound, Krauss said.

Homocysteine is a product of the metabolism of protein, but levels do not seem to be linked to overall protein in the diet. B vitamins affect it because they help break down homocysteine, Krauss said.

Scientists are still not sure if homocysteine causes some negative effect on the body, or if it is just a marker -- a signal that something else is wrong.

"This is entering into a whole new domain of nontraditional markers for heart disease," said Dr. Robert Eckel of the University of Colorado Health Sciences Center and chairman of the AHA nutrition committee.

Correspondent Rhonda Rowland and Reuters contributed to this story.