Can blood type affect personality and chemical reactions in the brain?
The answer with regard to brain chemistry is yes. Many studies have documented a link (probably genetic) between ABO group and certain differences in brain function, most commonly with regard to stress reactions. The Mind/Body Knowledge Base has a few links to collections of studies linking blood type to differences in adrenaline metabolism, cortisol breakdown and other brain/stress functions. With regard to personality, the data is less conclusive. There is an ongoing personality questionaire many people have filled out, and the results are available from the above link. Suffice it to say that personality is much more complicated and under a great number of influences.
