The association between increased alcohol use and light eyes may also be related to differences in neuron-firing speed (via Personality and Individual Differences). Melanin sheaths act as a protective cover for the connecting cables of our neurons. The more melanin we have in the front layer of the iris as well as in our central nervous system, the faster our neurons fire and can communicate with the brain. Compared to those with dark eyes, people with light eyes produce less melanin.
Researchers from a more recent 2015 study published in the American Journal of Medical Genetics: Neuropsychiatric Genetics (Part B) zeroed in even further on specific eye colors in relation to alcohol dependency. Compared to people with dark brown eyes, those with light eyes had higher rates of alcohol dependency. This included individuals with grey, green, and blue eyes, as well as those with brown in the middle of the eye. The strongest correlation was observed in people with blue eyes. While the study team emphasized that the exact cause of this connection remains unclear, they noted that it may have to do with two specific genes that reside close to each other on the same chromosome; one being responsible for eye color and the other being related to heightened alcohol tolerance.
If you or anyone you know needs help with addiction issues, help is available. Visit the Substance Abuse and Mental Health Services Administration website or contact SAMHSA’s National Helpline at 1-800-662-HELP (4357).