From Medical Daily:
But though your eye color may seem rather superficial, it can say a lot about your health too, in ways you may not have been aware.
This is because a variety of genes go into deciding your eye color. There aren’t just two genes — one for blue eyes and one for darker eyes as many scientists previously thought — but rather, there are up to 12 to 13 gene variations that can decide color. These genes linked to eye color are often at play in your body in different ways, which is why eye color can be a determinant of other health aspects. “These genes do other things in the body,” Dr. Jari Louhelainen... “One of them, NCX-4, which is linked to darker eyes, controls many proteins, of which one has recently been linked to pain.”
Our skin, hair, and eyes all get their color from a group of natural pigments called melanins. The amount of melanin in your iris defines whether you’re born with green, blue, or brown eyes. People who are born with a lot of melanin in the stroma of the iris tend to have brown eyes, while people with less melanin have green or hazel eyes, and finally, having no melanin typically leads to blue eyes. Eye color is unique for every individual (no one has the same exact color as anyone else) and it changes constantly, shifting shades over the period of a lifetime depending on your genes, diseases, and age. Below are some of the things your eye color can tell about you.
In 2008, scientists discovered that everyone who has blue eyes is genetically linked to the same common ancestor, a person who experienced a genetic mutation sometime between 6,000 and 10,000 years ago. Before this mutation, every human had brown eyes.
Some scientists may argue that your eye color can tell you something about how your pain tolerance. One study published earlier this year found that out of 58 women, those with light-colored eyes seemed to experience less pain when giving birth compared to those with dark-colored eyes. Not only did women with light-colored eyes experience less physical pain, but they also reportedly had less anxiety, depression, and negative thoughts. “
Other studies have hinted that your eye color may indicate something about how well you can handle booze, too. In the past, researchers have found that people with light-colored eyes were more likely to abuse alcohol than people with dark-colored eyes because they could handle larger amounts of alcohol.
A study conducted in Australia found that people with lighter eyes could be less “agreeable,” and far more competitive, than people with darker eyes. Agreeableness is a personality factor that is typically associated with empathy, friendliness, generosity, and compassion... but researchers believe it may have something to do with our evolutionary roots — thousands of years ago, our Northern European ancestors found light-colored eyes more attractive and ideal for mating. Thus, it's possible that blue-eyed people ended up having more of a competitive edge, at least in Northern Europe.
In addition, some studies have linked specific eye colors to diseases like diabetes, melanoma, and vitiligo. A 2012 study out of the University of Colorado School of Medicine found that people with blue eyes are less likely to have vitiligo, a skin condition that results in the loss of brown pigment from certain areas of the skin and leaves white blotches across some parts of the body.
People's eyes may change hues depending on how bloodshot they are or what shirt they're wearing, but having each eye be a different color — a condition called heterochromia — can also be indicative of certain diseases, such as Horner's syndrome, Fuch's heterochromic iridocyclitis, or pigmentary glaucoma. In addition, people with late-stage diabetes might notice their eyes darkening.
Having lighter eyes may also mean that you're more sensitive to the sun's UV rays, since they contain less pigment to protect them. As a result, those with blue, grey, or green eyes may have an increased risk for melanoma of the uvea, which is the middle layer of the eye.