People with blue eyes may have a greater risk of becoming alcoholics than those with darker eyes, according to the results of a new genetic analysis by researchers at the University of Vermont.
The study, led by Arvis Sulovari, a doctoral student in cellular, molecular and biomedical sciences, and Dr. Dawei Li, Ph.D., assistant professor of microbiology and molecular genetics, is the first to make a direct connection between a person’s eye color and their risk of developing alcohol dependence. The results of the research, published in this month’s issue of the American Journal of Medical Genetics: Neuropsychiatric Genetics (Part B), could move scientists one step closer to finding the roots of not only alcoholism, but also many other psychiatric illnesses.
The National Institute on Alcohol Abuse and Alcoholism (NIAAA) estimates that about 16.6 million adults and almost 700,000 youths in the United States suffered from an alcohol use disorder in 2013. Each year, nearly 88,000 Americans die from alcohol-related causes, making it the nation’s third leading preventable cause of death. While the causes of alcoholism are complex and not yet fully understood, past research has established that genetic factors account for approximately 50 to 60 percent of an individual’s risk of developing alcohol dependence — in fact, family history is the single-most reliable predictor of future alcohol problems.
Scientists have identified multiple genes that contribute to the risk of alcoholism. These include genes that increase a person’s risk, as well as those that may decrease that risk, directly or indirectly. For instance, some people of Asian descent carry a gene variant that alters their rate of alcohol metabolism, causing them to have symptoms like flushing, nausea, and rapid heartbeat when they drink. Many people who experience these effects avoid alcohol, which helps protect them from developing alcoholism.
Dr. Li notes that previous studies of individuals with European ancestry have shown that people with light-colored eyes tend to consume more alcohol than those with dark-colored eyes, but none have investigated whether there is a specific genetic link between eye color and alcohol dependence. 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.
Using the database, the researchers identified over 1,200 people with European ancestry who suffered from alcohol dependence. Once the team recognized an eye color connection, they reanalyzed their data three times, comparing the participants’ age, gender and differences in backgrounds and locations. The analysis revealed that European Americans with light-colored eyes had a higher rate of alcohol dependence than those with dark brown eyes. Blue eyes were most strongly linked to this condition, the researchers found. These results remained even after accounting for confounding factors like age, gender, ethnicity and geographical location.
As it turns out, the genetic components that determine eye color overlap with genes related to excessive alcohol use, the authors explained. “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.
Although the study did not show a cause-and-effect link between eye color and alcoholism risk, Sulovari says the findings “suggest an intriguing possibility that eye color can be useful in the clinic for alcohol dependence diagnosis.”
Indeed, eye color is already used as an indicator of risk for certain health conditions. For example, those with lighter iris color have been found to have a higher prevalence of age-related macular degeneration (ARMD) than those with darker iris color. Additionally, having blue or gray eyes is considered a risk factor for uveal melanoma and ocular melanoma. And according to a study published in the American Journal of Ophthalmology, people with dark brown eyes are at increased risk of developing cataracts, and therefore should protect their eyes from direct exposure to sunlight.