WASHINGTON -- While cholesterol and heart disease are linked in
the minds of many as closely as smoking and lung cancer, another
substance circulating in the blood may actually be a better
predictor of heart attacks, strokes and even seemingly unrelated
conditions like high-risk pregnancies and Alzheimer's disease.
Homocysteine, a byproduct of meat metabolism, has become a
popular focus of study in recent years because of its close
association with cardiovascular disease. And the good news is that
something as simple as increasing the consumption of vitamin B and
folic acid lowers homocysteine levels and could help prevent
ailments associated with it.
Now that tests have become relatively cheap ($50 to $150),
widely available and reliable, the impetus to begin testing at
least those in high-risk groups is growing, according to scientists
speaking here last Thursday at the American Association for the
Advancement of Science meeting.
``Anybody who is at risk for cardiovascular disease, who has
present atherosclerosis or a family history of atherosclerosis --
those are candidates for homocysteine testing,'' said Donald
Jacobsen, a researcher at the Cleveland Clinic Foundation.
The precise way homocysteine may be related to disease is not
yet understood. Some believe it generates oxygen-free radicals that
damage the endothelial cells that line blood vessels, leading to
clots and clogs. Another theory suggests it interferes with
molecules in the blood like nitric oxide that are involved in
relaxing blood vessels.
One thing is clear, though: Study after study has shown a strong
correlation between people who have high homocysteine levels in
their blood and heart disease. And among a large group of nurses,
researchers found that those who took multivitamin pills reduced
the chance of having a heart attack by 25 percent.
With the introduction of homocysteine tests in the late 1980s,
research in this area has skyrocketed. Scientists now are
publishing an average of one paper a day on it, according to M.
Rene Malinow, professor of medicine at Oregon Health Sciences
University.
Several clinical trials are under way in the United States,
Europe, South Africa and Australia to test whether vitamin B and
folic acid supplements and their associated lowering of
homocysteine leads to less cardiovascular disease. The first
results are expected in about three years.
``My tentative prediction is that universal homocysteine testing
and treatment ... may be incorporated into medical practice and
public health if any of the clinical trials demonstrate that B
vitamins have a beneficial affect on atherosclerosis disease,''
Malinow said.
For the past two years, enriched flour sold in the United States
contains extra doses of folic acid, which is known to prevent spina
bifida and related birth defects. Such defects, too, may be related
to high homocysteine levels in pregnant women.
Aleksandar Rajkovic of the Baylor College of Medicine in Houston
has been studying the relationship of homocysteine to problems
during pregnancy, including preeclampsia, a dangerous elevation of
blood pressure. He said associations have also been made with
miscarriages.
``Ten to 30 percent of patients who have reproductive problems
have elevated homocysteine,'' Rajkovic said.
However, research in this area is much less comprehensive than
that involving heart disease. More recently, studies have been
published linking high homocysteine to Alzheimer's disease.
It is known than homocysteine levels rise over a person's
lifetime. A 3-year-old whose level is 5 micromols per liter (a
measurement based on molecular weight) would probably reach 25 by
the time he or she was 100, Jacobsen said. Women tend to have lower
rates than men, but that discrepancy begins to disappear after
menopause.
