Researchers from Harvard have discovered that blood type influences the risk of cardiovascular disease. The study showed that people with A, B, or AB blood types had a greater risk of coronary heart disease than people with an O blood type.

The findings are based on data analyzed from two of the largest, most well-known retrospective observational studies in the US. The studies had observed 90,000 people between the ages of 30 and 75 for a period of 25 years.

Researchers discovered that those with the highest increased risk had AB blood type, which also happens to be the rarest blood type (about 7% of the U.S. population). Those who have AB displayed a 23% increased risk of the condition, compared with the more commonly found type Os. Meanwhile, people with type B blood had an 11% higher risk of coronary heart disease, and people with type A blood had a 5% higher risk compared with people with type O blood.

The findings have been published in Arteriosclerosis, Thrombosis and Vascular Biology.