Several older studies—we’re talking 1970s and ’80s—found weak associations between blood type A and higher rates of alcoholism. More research has linked specific blood components called antigens to the disease. These studies suggest type A antigens may alter your immune system’s reaction to alcohol in ways that affect intoxication. Also, genetic factors make up about 50% of your risk for alcoholism, according to the National Institutes of Health. All of this suggests biology plays a role in your risk, though specifics are murky. See last post for association between Rh negative blood factor and heavy drinking.