Researchers from the University of Vermont in Burlington have suggested a somewhat surprising way to identify a person's risk of alcohol dependence: eye color.
Their study, published in the American Journal of Medical Genetics: Neuropsychiatric Genetics (Part B), suggests people with light-colored eyes are more likely to be alcohol dependent than those with brown eyes, with blue-eyed individuals at highest risk.
The research team - led by Arvis Sulovari, a doctoral student in cellular, molecular and biomedical sciences, and Dawei Li, assistant professor of microbiology and molecular genetics - says their study is the first to make such an association.
According to the National Institute on Alcohol Abuse and Alcoholism, around 16.6 million adults and almost 700,000 youths in the US had an alcohol use disorder in 2013. Each year, nearly 88,000 people die from alcohol-related causes, making it the third leading preventable cause of death in the US.
Sulovari, Li and their team note that previous research in individuals of European ancestry has shown that people with light-colored eyes tend to consume more alcohol than those with dark-colored eyes, but they note that no studies had investigated whether there is a link between eye color and alcohol dependence.
Genetic link between eye color and alcoholism
To find out, the researchers analyzed information from a clinical and genetic database of more than 10,000 people who had been diagnosed with at least one psychiatric illness, including depression, schizophrenia, bipolar disorder and drug or alcohol dependence.
"These are complex disorders," says Li. "There are many genes, and there are many environmental triggers."
The team included 1,263 alcohol-dependent Americans with European ancestry in their final analysis, and assessed the genetic samples of each individual.
The results revealed that individuals with light-colored eyes - particularly those with blue eyes - were at higher risk of alcohol dependence than people with brown eyes. These results remained after being retested three times, accounting for subjects' age, gender, ethnicity and geographical location.
Commenting on the findings, Sulovari says:
"This suggests an intriguing possibility - that eye color can be useful in the clinic for alcohol dependence diagnosis."
In addition, the team identified associations between genes related to eye color and genes related to alcohol dependence. "We found evidence of linkage disequilibrium between an alcohol dependent-associated GABA receptor gene cluster, GABRB3/GABRG3, and eye color genes, OCA2/HERC2, as well as between alcohol dependent-associated GRM5 and pigmentation-associated TYR," they explain.
The team says the mechanisms underlying the link between eye color and alcohol dependence are unclear, and more studies are needed to better understand the association.
Still, they suggest their results may help uncover the genetic roots of alcoholism as well as other psychiatric disorders.
Last month, Medical News Today reported on a study published in JAMA Psychiatry, in which researchers claim 1 in 3 Americans are affected by alcohol use disorders in their lifetime.