DALLAS -- Here's another reason to know your blood type -- it might be a clue to your risk of heart disease.
People with blood types A, B or AB have a slightly higher risk of heart disease than those with type O, which is the most common, according to research released Tuesday.
Those who know they are at higher risk may be more motivated to make changes to lower their chances of heart disease, said Dr. Lu Qi, senior author of the study from the Harvard School of Public Health in Boston.
"We cannot change blood type, but we can change lifestyle," said Qi, who led a study released last year showing that blood type may affect stroke risk.
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The new study involved about 90,000 men and women in two observational health studies that cover more than 20 years. Combined, 4,070 people developed heart disease. The researchers considered age and other factors, like diet, drinking and family history of heart attacks.
The increased risk for type A was 8 percent; type B, 11 percent; and type AB, 20 percent.
The trend held up when the researchers compared their results with several other population studies recording the same factors.
Across a total of seven studies, the risk for people with non-O blood types was 11 percent higher.
Rh factor -- the "positive" or "negative" often included in blood typing -- was not correlated with any differences in heart disease risk.
The analysis was not designed to identify why blood type might influence heart disease risk.
But the researchers noted that non-O individuals have higher levels of two proteins involved in clotting and atherosclerosis -- and that people with type A blood, in particular, have been reported to have higher levels of serum total cholesterol and LDL (bad) cholesterol.
While the study did not examine how blood type may affect heart disease risk, it noted that research has shown that some characteristics of different types may be a factor. For instance, some research suggests that blood types might affect cholesterol levels or the risk of developing blood clots.
The findings were published in the American Heart Association journal Arteriosclerosis, Thrombosis and Vascular Biology.
In a statement released by that organization, Harvard's Qi said that learning more about the relationship between blood type and heart disease risk could help doctors tailor their advice -- perhaps urging patients with type A blood to watch their cholesterol more carefully, for example.
"Our findings might help physicians better understand who is at risk for developing heart disease," he said.
"It's good to know your blood type the same way you should know your cholesterol or blood pressure numbers. If you know you're at higher risk, you can reduce that risk by adopting a healthier lifestyle, such as eating right, exercising and not smoking."
A doctor not involved in the study cautioned that the increased risk for non-O blood types is modest and that other risk factors have a bigger impact.
"Most of things that are this modest, most of the time they don't meaningfully change how you'd think about your risk overall," said Dr. Amit Khera, director of the preventive cardiology program at the University of Texas Southwestern Medical Center at Dallas.
Type O is the most common blood type, followed by A, B and AB. About 45 percent of Anglos, 51 percent of blacks, 57 percent of Hispanics and 40 percent of Asians have blood type O, according to the American Red Cross.
Type A: 40 percent of Anglos, 26 percent of blacks, 31 percent of Hispanics and 28 percent of Asians.
Type B: 11 percent of Anglos, 19 percent of blacks, 10 percent of Hispanics and 25 percent of Asians.
Type AB: 4 percent of Anglos and blacks, 2 percent of Hispanics and 7 percent of Asians.
This report includes material from the Los Angeles Times.