The finding that blue-eyed people have a greater tendency towards alcoholism has come from geneticists working at the University of Vermont. The finding is that European-Americans with blue eyes are most likely to have a greater dependency for alcohol than people with other eye colors. Eye color is caused by pigmentation of the iris and the degree of light scattering by the liquid in the stroma of the iris.
The finding has come about through computer modeling. For this, the research group took a genetic database containing some 10,000 northeastern Americans who had been diagnosed with one or more types of psychiatric illness. They then filtered out European-Americans who had also been diagnosed as alcoholics. Several exercises is sorting the data produced the same outcome: a high correlation between people sporting blue eyes and a higher chance of alcoholism.
In the paper the authors write that they found: “a statistically significant number of genetic interactions between eye color genes and AD (alcohol dependent)-associated genes.”
Of course the research was not concluding that everyone with blue eyes is an alcoholic; what it was arguing is that there is a genetic link that means that someone with blue eyes is more likely to become addicted to alcohol than someone who does not have blue eyes. For this to happen, a number of social factors would need to be accounted for and a regular and excessive level of alcohol consumed. So the link remains one of correlation rather than of causation. The researchers have not put forward any theory relating to any biological mechanism involved. Furthermore, the data relates to the U.S. and Canadian population only. The researchers are clear that the finding is intended to be the start of further investigation, rather than a conclusive and deterministic connection.
The findings have been published in the journal American Journal of Medical Genetics: Neuropsychiatric Genetics (Part B). The research paper is “Eye color: A potential indicator of alcohol dependence risk in European Americans.”