When it comes to lipid profiles -- a key measure of heart disease risk-- it appears that African-Americans and women have it better than whites and men, according to a new study by Duke University Medical Center researchers.
Not long ago, one's lipid profile was a simple number produced by adding together the levels of high-density lipoproteins (HDL) and low-density lipoproteins (LDL), the so-called "good" and "bad" forms of cholesterol. However, researchers have now identified five subclasses of HDL, four subclasses of LDL, as well six subclasses of very low density lipoproteins (VLDL), as well as intermediate-density lipoprotein (IDL). In addition to the levels of the lipoproteins, also critical is the size of the particles they form in the blood.
In a study that takes these new subclasses into account, the Duke researchers have found that there are racial and gender differences in the sizes and numbers of the particles of these lipoproteins. Furthermore, they said, these differences can determine one's risk of developing cardiovascular disease. These differences help explain why two people with the same overall cholesterol level can have markedly different degrees of cardiovascular disease, the researchers said.
"It is important to know these differences, because the commonly used lipid profiles do not always tell the complete story," said Johanna Johnson, Duke exercise physiologist and first author of a paper published in the October, 2004, issue of the journal Atherosclerosis. "Generally speaking, African-American women have the best lipoprotein distribution, while white men have the worst profile.
"Our data would suggest that the subclass profile of the women in our study would place them at reduced risk for heart disease, even though their total cholesterol and LDL levels are higher than men," she continued. "Additionally, the significant racial difference seen among the LDL and VLDL subclasses would appear to put whites at more risk. These gender and racial differences would not be apparent in traditional lipid profiles."
The Duke team studied 285 sedentary and overweight men and women without a history of heart disease or diabetes as a part of one of the first large-scale clinical trials designed to measure the effects of differing amounts and intensities of exercise on the average American couch potato.
The trial, led by Duke cardiologist William Kraus, M.D., was support by a $4.3 million grant from the National Heart, Lung and Blood Institute. Dubbed STRRIDE (Studies of Targeted Risk Reduction Interventions through Defined Exercise), the five-year trial began in 1998.
"While others studies have suggested that in terms of lipid profiles, African-Americans are better off than whites and women are better off than men, what has not been known before is the distribution of the different particle size and number," Kraus said. "No matter how we look at it, white men have the higher risk of developing metabolic syndromes, diabetes and cardiovascular disease. When it comes to lipids, white men are cesspools."
Cholesterol and triglycerides are energy-rich fats, or lipids, that must "attach" to protein particles in order to circulate throughout the bloodstream and nourish tissues. Abnormal levels of these lipoprotein units have been linked to the progression of atherosclerosis and heart disease.
"It is known that small, dense LDL particles are associated with increased risk for cardiovascular disease, and our study found that men have higher levels of these particles compared to women, and that whites have higher levels than African-Americans," Johnson said. "Additionally, the white men in our study had 2.5 times higher levels of these small dense particles than any other group."
While the researchers found no difference between African-American and white men in terms of LDL particle concentration, they did find that African-American women tended to have larger LDL particle sizes with lower amounts of small LDL particles than white women.