WEDNESDAY, Nov. 26, 2003 (HealthDayNews) -- A specific kind of low-density cholesterol is an accurate indicator of increased risk of heart attack and stroke in older men, but not women, says a new study that has researchers scratching their heads in puzzlement.
"I don't know why" the difference exists, says Dr. Abraham A. Ariyo, lead author of a report on the study in the Nov. 27 issue of the New England Journal of Medicine.
Nevertheless, testing older men for blood levels of the substance, Lp(a) lipoprotein, could help doctors identify those who require special attention to prevent heart attack, stroke and other cardiovascular problems, Ariyo says.
Such a test would be useful because "the factors that predict cardiovascular risk in older people are not well known," he says. Most hospital laboratories are equipped to do the test, he adds.
Ariyo did the study when he was at Johns Hopkins Hospital in Baltimore. He now is director of HeartMasters, a cardiovascular prevention group in Dallas.
He says he studied Lp(a) lipoprotein because "there has been a lot of controversy about whether it carries cardiovascular risk. Some data says yes, some data says no."
Lp(a) lipoprotein is a member of the family of LDL cholesterol molecules, which form the fatty plaques that can block arteries. Ariyo and his colleagues began measuring blood levels of the substance in 5,888 heart-healthy men and women 65 and older, then followed them for an average of 7.4 years.
Men with the highest levels of Lp(a) had three times the risk of stroke, almost three times the risk of death from cardiovascular disease, and nearly twice the risk of death from all causes over that period, after adjustment for other risk factors, such as smoking.
"Similar analyses for women, which also included adjustment for estrogen use or nonuse, revealed no such relation," the report says.
Dr. Angelo Scanu, director of the University of Chicago Hospitals Lipid Clinic and the author of an accompanying editorial, says there is no ready explanation for that difference.
The reported results are not in doubt, because it came from "a large study done by competent people," Scanu says, but "there is no basic understanding of the mechanism."
One possibility, he says, is that "it may reflect influences by other genes and environmental factors." It's also possible that the difference has something to do with the factors that allow people to survive into very old age, he adds.
"I don't believe we can draw firm conclusions from this study," he says. "We need further information. We know that Lp(a) is a problem in ages less than 55. After that our ignorance grows enormously."
A better understanding is urgently needed, Ariyo says, because the fastest-growing population in the United States is the 85-and-older age group.
An explanation of Lp(a) lipoprotein's place among the good and bad cholesterols can be found at the American Heart Association, while the American Association for Clinical Chemistry explains testing for LDL cholesterol.