Do you have brown eyes and blues during the winter? There may be a link between the two! Dark eyes, which are less sensitive to light than light eyes, appear to be associated with a higher risk of seasonal depression.
Our mood varies with the seasons, but this phenomenon is more pronounced in some people who suffer from seasonal depression or “Seasonal Affective Disorder” (SAD). During the winter months, this recurrent depression is characterized by a bad mood.
The prevalence of this disorder remains rather vague in general, it is estimated that 1 to 10% of the population suffers from it. When symptoms are mild, the CAS is referred to as “winter blues.” The exact causes of this seasonal depression remain unclear, although a link with the decrease in brightness is suspected.
In an article published in The Conversation, Lance Workman, professor of psychology at the University of South Wales, offers another explanation: the color of the eyes would influence the risk of seasonal depression.
175 students from two universities, one in Wales and the other in Cyprus, took part in this work. They lived at different latitudes (51 ° and 35 ° North, respectively).
The objective was, among other things, to test the hypothesis that, the further one moves away from the equator, the more risks the seasonal depression. There is a questionnaire, the Seasonal Pattern Assessment Questionnaire (SPAQ ), which is used to diagnose seasonal depression.
A high score on this questionnaire indicates a more severe SAD. According to the results obtained in this study, the latitude did not affect contrary to the color of the eyes. Clear-eyed participants had lower questionnaire scores than those with dark eyes: brown eyes were more depressed.
Evolution would have favored blue eyes at high latitudes
But, how can the color of the eyes influence our mood? In the eye, photosensitive cells in the retina transform visual information into an electrical signal that allows the brain to reconstruct an image. Some cells in the retina send a message to the hypothalamus, a region of the brain, about the amount of light.
As light eyes are more sensitive to light, according to Lance Workman,
“That means they do not need to absorb as much light as brown or dark eyes before this information reaches the retinal cells. Thus, people with lighter eyes release less melatonin (Melatonin is a hormone, produced primarily by the pineal gland, which regulates wakefulness.) during the fall and winter. This mechanism may give people with clear eyes some flexibility to seasonal affective disorder (although a lower proportion may still suffer from SAD). “
For the researcher, the blue eyes would be the consequence of a mutation that also gave a clearer skin. This genetic evolution would have allowed populations to produce more vitamin D, from sunlight in regions that are less sunny in winter.
But the color of the eyes is indeed not the only cause of the seasonal depression. People who stay too much indoors are also more prone to this disorder. Also, in winter, leave your home to enjoy the light when the weather is sunny. The therapy is also known to treat SAD.