"There are some interesting ethnic differences in cardiovascular risk factors, including the fact that blacks tend to have higher HDL (high-density lipoprotein) and lower triglycerides, which is an advantage, and we suspect it is due to genetic influences," says Dr. Catherine L. Davis, clinical health psychologist at the Medical College of Georgia.
Coronary artery disease rates in the United States are similar or lower in blacks yet blacks have higher mortality rates.
Dr. Davis and her colleagues at MCG's Georgia Prevention Institute examined heritability - the percentage of a variable attributable to genes - to better understand the influence of genetics and environment on heart health.
Heritability studies were enabled by data MCG is collecting on 500 pairs of twins - blacks and whites, identical and fraternal - to determine whether environmental stress is a risk factor for cardiovascular disease. Identical twins have identical genes and fraternal twins share about 50 percent of their genes, much like normal siblings.
"Any differences between identical twins must be due to the environment," says Dr. Harold Snieder, genetic epidemiologist. "So you can quantify the part that is due to genetics," he says, noting that heritability provides an aggregate look at the effect of genes, many of which may still be unknown.
Across both races they found that lipid levels, which include so-called good cholesterol, HDL, and bad cholesterol, LDL, as well as triglycerides, are 60 percent to 80 percent determined by genetics.
A separate study found heart rate variability - the heart's ability to respond to changing demands - was heritable and equally so, about 70 percent, among young blacks and whites, Dr. Snieder says.