Researchers have pointed out that it is important to know one's blood type. When Harvard scientists ＿＿（46）＿＿ more than two decades of data on more than 77,000 people, they found that people with type AB blood had a 23 percent increased risk for heart disease compared to people with type O blood. ＿＿（47）＿＿ with type B blood had an 11 percent higher risk and people with type A blood had 5 percent greater risk of heart disease. Researchers aren't sure ＿＿（48）＿＿ , though. But they posit that type A blood is associated with LDL cholesterol and that type O blood, ＿＿（49）＿＿ is associated with reduced risk, may contain a chemical that boosts blood flow and prevents clots. However, researchers are quick to point out that lifestyle factors ＿＿（50）＿＿ weight, smoking, and diet, which, unlike blood type, are modifiable and have a much greater impact on heart disease.