ROANOKE TIMES
Copyright (c) 1997, Roanoke Times
DATE: Tuesday, March 4, 1997 TAG: 9703040036
SECTION: EXTRA PAGE: 3 EDITION: METRO
COLUMN: personal health
SOURCE: JANE BRODY
When someone has a heart attack or stroke, it is common to wonder what might have set it off. Was it smoking, high cholesterol, obesity, diabetes, high blood pressure, inactivity, heredity, old age?
In many instances, these cardiovascular events seem to happen out of the blue to people without any of the well-known risk factors.
But these risk factors are not the only ones. Consider homocysteine, an amino acid that has recently been linked to as many as one in five heart attacks and strokes. Some researchers now say that homocysteine may be as important a risk factor for vascular disease as smoking and even more important than high cholesterol levels.
While the case against homocysteine has not been proved to the satisfaction of experts in the field, strong circumstantial evidence continues to pile up. It is so convincing that even some usually wary researchers are suggesting that Americans would be wise to increase their consumption of foods and supplements containing folic acid, a B vitamin that can reduce homocysteine levels in the blood.
The story of homocysteine as a risk factor nearly parallels that of cholesterol. In decades past, a serum cholesterol level in the 240-milligram range, now known to be a heart hazard, was called ``normal'' because it was found in the average middle-aged American man. Eventually, researchers realized that these ``normal'' cholesterol levels were likely to lead to heart disease, often showing up as heart attacks in midlife.
Likewise, the levels of homocysteine now linked to heart attacks and strokes were, until recently, listed as ``within normal range'' on blood tests. Again, what was thought to be normal for middle-aged Americans turns out to be high and potentially hazardous.
The first hint of vascular trouble resulting from high homocysteine levels came in 1969, when Dr. Kilmer McCully, now a pathologist at the Veterans Affairs Hospital in Providence, R.I., reported finding arterial disease in an infant who had died from a rare metabolic defect that resulted in very high levels of homocysteine.
The baby had severe arteriosclerosis, similar to the arterial disease seen in young people with a better-known inborn disorder, homocystinuria, which also results in extremely high blood levels of homocysteine. McCully proposed that very high levels of homocysteine caused vascular disease.
But not until the 1990s did elevated homocysteine levels begin to be recognized as a potentially widespread risk factor. The evidence, which has been remarkably consistent, comes from both laboratory and human studies. More than 20 studies comparing people who had suffered heart attacks or strokes with those who were healthy have found higher blood levels of homocysteine in patients than in the healthy control subjects.
Two studies that tracked the fates of many thousands of initially healthy individuals have corroborated these findings. One, the Physicians' Health Study by Dr. Meir Stampfer and colleagues at the Harvard School of Public Health and Brigham and Women's Hospital in Boston, found that men with homocysteine levels in the top 5 percent of the group faced a threefold greater risk of suffering a heart attack than men with lower levels, even when other risk factors were taken into account. Similar results were found in a large study in Norway.
Among participants in the Framingham Heart Study, much higher rates of atherosclerosis in the arteries feeding the brain were found among those with high blood levels of homocysteine.
This study, by Dr. Jacob Selhub and colleagues at the Department of Agriculture's Human Nutrition Research Center on Aging at Tufts University in Boston, also found that people with little folic acid in their diets and blood had the highest homocysteine levels.
As might be predicted from the Framingham findings, separate studies in Baltimore and in Bergen, Norway, have linked high homocysteine levels to an increased risk of stroke in young women and middle-aged men.
In laboratory and animal studies, high levels of homocysteine damaged the lining of blood vessels and increased the likelihood of blood clots, which could account for its role in vascular disease.
A recent report from researchers in Dublin traced moderately high homocysteine levels to a common gene mutation that results in a defective enzyme involved in homocysteine metabolism. This defect, they reported, is significantly more common among patients with heart disease than among healthy people. Moderately high levels of homocysteine are also found in people who carry a single gene for homocystinuria; two such genes are needed to cause the severe metabolic disorder.
But while genetics may be involved in some or all people with high homocysteine levels, diet clearly plays an important role, both as a cause and a treatment. Elevated levels of homocysteine are associated with an inadequate intake of certain B vitamins, particularly folic acid and to a lesser extent, B-6 and B-12. Folic acid, as folate, is most abundant in dried beans and peas, enriched whole-grain cereals, nuts and seeds, dark green, leafy vegetables and orange juice.
In a move that homocysteine researchers regard as unfortunate, the Food and Nutrition Board of the National Academy of Sciences, in its last rendering of Recommended Dietary Allowances, reduced the RDA for folic acid from 400 micrograms a day to 200 micrograms for men and 180 micrograms for women.
Yet homocysteine levels were elevated among the elderly in Framingham who consumed 280 micrograms of folic acid each day. Selhub and his colleagues estimated that two-thirds of those with high homocysteine levels consumed low or moderate amounts of one or more of the three B vitamins.
The good news is that regardless of what may cause a rise in homocysteine, consuming more folate or folic acid can reduce it. In treating elevated levels, doctors generally prescribe a supplement of one gram of folic acid daily, continued indefinitely.
For the average healthy person, experts suggest eating more folate-rich foods each day. Stampfer has calculated that eating the recommended five servings of fruits and vegetables a day ``would bring the folate and vitamin B-6 intakes of most persons to levels adequate to prevent high homocysteine levels.''
For those who cannot or will not make the needed dietary adjustments, Stampfer suggests taking a daily 400-microgram supplement of folic, acid along with a small amount (six micrograms), of vitamin B-12, because taking folic acid can mask a deficiency of B-12.
Dr. Robert Russell of Tufts estimated that raising folic acid intake to 400 micrograms a day could prevent at least 13,500 deaths from heart attack alone each year. Currently, only about 40 percent of Americans consume that amount. - New York Times Syndicate
LENGTH: Long : 116 linesby CNB