TUESDAY, Sept. 19, 2006 (HealthDay News) -- Women who have high levels of a little-known lipoprotein face a higher risk of heart attacks and strokes, a new study suggests.
And when a high reading on what is called lipoprotein (a) is accompanied by high levels of "bad" cholesterol, women are in even more cardiovascular danger.
"Lipoprotein (a) is a protein that tends to be measured in hospital patients," said study author Dr. Jacqueline Suk Danik, whose report is published in the Sept. 20 issue of the Journal of the American Medical Association. It's not routinely measured, and so many people have never heard of it, explained Danik, a cardiologist at Brigham and Women's Hospital, in Boston. Like other lipoproteins, it carries fats through the blood.
Studies on lipoprotein (a) and its value as a predictor of cardiovascular risk in both men and women have yielded conflicting results over the years. Part of the problem, Danik said, is that the protein is hard to measure partly because the size of the protein varies from person to person. Another challenge is that a variety of different tests to measure the protein exist, and there is no gold standard screen for it.
But Danik and her colleagues took advantage of a new, more accurate test to measure it, evaluating nearly 28,000 initially healthy women who took part in the Women's Health Study. The women joined it between 1992 and 1995, donating blood specimens, and were followed up for 10 years to evaluate a number of health issues. Danik's team tested stored blood samples of all 28,000 for lipoprotein (a) to see if those with high levels were more likely to suffer cardiovascular problems. During the follow-up, there were 899 cardiovascular "events," such as stroke or heart attack.
They found women with high levels of lipoprotein (a) did indeed have a higher chance of suffering heart problems or strokes. "Women who had levels greater than 30 (milligrams per deciliter), which is the standard for being high, did have a slightly higher risk of cardiovascular events during the 10 years we followed them," Danik said.
If the levels were very high, the risk of stroke or heart attack was even greater, she said. "Women with very high lipoprotein (a), in the top 10 percent, which in this case meant a reading above 65 milligrams per deciliter, was associated with a 67 percent higher risk of developing a heart attack or an ischemic stroke, requiring cardiovascular intervention such as surgery or angioplasty or dying from cardiovascular disease, compared to women who had low lipoprotein (a)," she noted.
If women also had high levels of LDL cholesterol, it was a double whammy, the researchers found. "Women with lipoprotein (a) greater than 65 milligrams per deciliter and LDLs higher than the median value, around 120 milligrams per deciliter, had an 80 percent higher risk of developing the same events," Danik said.
For the general population, LDL levels are considered optimal if below 100 by the National Heart, Lung, and Blood Institute.
The new study is a valuable addition to research, said Dr. Karol Watson, an assistant professor of cardiology at the University of California, Los Angeles, David Geffen School of Medicine.
"Even in the world of preventive cardiology, we have not known what to do with lipoprotein (a)," she said. "Data about lipoprotein (a) as it correlates to heart disease is mixed. In African-Americans, for instance, some studies show it is not even a risk. And in women, the effects are not found to be as robust as in men."
However, she said, "Most of us have believed that lipoprotein (a) is an important risk factor. This is one more piece of compelling research that says, yes, it is a risk factor for certain individuals. One of the study's strengths is it's a huge population."
But Watson and Danik agreed the study doesn't mean routine testing of lipoprotein (a) levels is warranted, at least not yet. The test is best reserved, they said, for those with a strong family history of cardiovascular disease, those diagnosed with cardiovascular disease without any obvious risk factors (such as high blood pressure), and those who keep having heart attacks and strokes even if they are receiving medical care to control their risk factors.
To learn more about lipoprotein (a), visit the Cleveland Clinic.