Homocysteine May Trigger Strokes
Friday, February 16th 2001, 12:00 am
News On 6
FORT LAUDERDALE, Fla. (AP) â€” Evidence is building that high levels of the amino acid homocysteine, long implicated in heart attacks, also increase the risk of strokes.
The possible link between homocysteine and strokes is controversial, in part because no one knows for sure whether the substance actually causes them or whether lowering it protects against strokes.
However, several studies released Thursday at a meeting of the American Stroke Association in Fort Lauderdale build the circumstantial case that homocysteine is indeed a factor underlying strokes, the leading cause of permanent disability.
Genes and living habits can make homocysteine levels rise in the bloodstream. ``We need to identify whether it definitely is a risk factor or not, how big it is, can we modify it and do we decrease the risk of stroke,'' said Dr. Ralph Sacco of Columbia University.
One way to lower homocysteine is to increase doses of the B vitamins â€” folic acid and vitamins B-6 and B-12. A major study under way called VISP â€” Vitamin Intervention for Stroke Prevention â€” is testing whether extra doses of these vitamins ward off new strokes in those who have already suffered them.
Evidence of homocysteine's importance comes from a new analysis by Dr. Peter J. Kelly of Massachusetts General Hospital in Boston. His team combined the results of 14 studies involving more than 11,000 patients.
Together, they suggest that people with high levels of homocysteine have a 75 percent higher risk of stroke than do those with average levels. The chance this was a statistical fluke was less than one in 10,000.
The analysis also showed that people who suffer strokes have average homocysteine levels that are 18 percent higher than those who do not.
Dr. Edwould J. von Dijk of Erasmus Medical Center in the Netherlands looked for evidence of small, symptom-free strokes in the brains of 1,077 elderly people. It found that these were twice as common in those with high homocysteine levels.
A study by Dr. Souvik Sen of the New Jersey Neuroscience Institute of Edison, N.J., suggests one way that high homocysteine levels might be bad. Buildups of fatty deposits in the aorta, the main artery leaving the heart, can trigger strokes if globs break off and drift to the brain.
Sen studied 78 victims of strokes and mini-strokes. He found that those in whom this buildup worsened were more likely to have high homocysteine levels.
However, some of these studies might be complicated by the fact that a stroke itself can increase homocysteine levels. Virginia J. Howard, an epidemiologist from the University of Alabama at Birmingham, analyzed preliminary data from VISP and found that homocysteine levels go up about 20 percent during the two weeks following a stroke.
``This raises questions about cause and effect,'' she said. ``Which came first?''
Genes can raise homocysteine levels, as can B vitamin deficiency, kidney disease, aging and possibly alcohol abuse and lack of exercise, among other things.
To help protect against birth defects, the Food and Drug Administration ordered manufacturers to begin fortifying flour, rice and other grain foods with folic acid in 1998. This appears to be having the added benefit of lowering homocysteine levels.
A study last year of white, middle-aged residents of Framingham, Mass., found that average blood levels of folic acid doubled and average homocysteine levels fell about 7 percent after the change in food.
While grain foods, such as breakfast cereal, have become a primary source of folic acid, vitamin B-6 comes mostly from fruits and vegetables and vitamin B-12 from red meat. All of these are also found in multivitamins.
No one knows precisely what the ideal homocysteine level is. However, doctors estimate that one-quarter of the U.S. population has clearly elevated levels.