Here’s another reason to know your blood type — it might be a clue to your risk of heart disease.

People who have blood types A, B, or AB have a slightly higher risk of heart disease compared to those with type O, the most common kind, according to a research study.

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 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 that showed blood type may affect stroke risk.

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, family history of heart attacks that could contribute to heart disease.

The increased risk for type A was 8 per cent; type B, 11 per cent; and type AB, 20 per cent.

While the study did not examine how blood type may affect heart disease risk, it noted that research has shown 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.

A doctor not involved in the study cautioned that the increased risk for non-O blood types is modest, and that other risk factors like smoking 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 Programme at the University of Texas Southwestern Medical Centre in Dallas.

“This shouldn’t cause much alarm for most of the population,” he added.  No matter what blood type, Harvard’s Qi said everyone should pay attention to risk factors they can change, including smoking, weight, high cholesterol, high blood pressure and a sedentary lifestyle.

Type O is the most common blood type, followed by A, B and AB. About 45 per cent of whites, 51 per cent of blacks, 57 per cent of Hispanics and 40 per cent of Asians have blood type O, according to the American Red Cross.

Type A: 40 per cent of whites, 26 per cent of blacks, 31 per cent of Hispanics and 28 per cent of Asians.

Type B: 11 per cent of whites, 19 per cent of blacks, 10 per cent of Hispanics and 25 per cent of Asians.

Type AB: 4 per cent of white and blacks, 2 per cent of Hispanics and 7 per cent of Asians.