You are not alone if the colder weather and longer nights make you feel down. This well-known phenomenon, referred to as Seasonal Affective Disorder (SAD), can explain why people experience feelings of sadness, irritability, and apathy during the winter months. For some, the condition can be severe and debilitating.
Although SAD is a recognized form of clinical depression, experts still hold differing views about its causes, with some even questioning its existence. However, research by neuroscientist Lance Workman has discovered that your eye color may actually be a determining factor in whether you develop SAD.
A survey conducted by Lance Workman in 2014 found that about 8% of the UK population self-reported seasonal changes that could be classified as SAD. An additional 21% reported symptoms of SAD under syndrome, a less severe form commonly referred to as “winter blues.”
While many may suspect they have SAD, the condition is often diagnosed using a questionnaire that evaluates seasonal patterns. This requires individuals to answer a series of questions about seasonal behavior, mood, and changes in habits. The higher the score on the questionnaire, the more severe the individual’s SAD symptoms are likely to be. However, these diagnostic tools can vary between organizations, which sometimes leads to inconsistent diagnoses.
Eye color may be a determining factor in whether you develop SAD.
But what truly causes SAD remains a topic of debate. Some theories, such as the latitude hypothesis, suggest that SAD is triggered by reduced exposure to sunlight during winter. This implies that SAD should be more prevalent in countries located far from the equator (such as Iceland). However, some studies have failed to support this theory. Another hypothesis posits that SAD occurs when our biological rhythms are disrupted as the days shorten.
Other theories suggest it arises from an imbalance of serotonin and melatonin in the body. Serotonin gives us energy, while the release of melatonin makes us feel sleepy. Since melatonin is produced from serotonin, individuals with SAD may produce excessive melatonin during the winter months, leading to feelings of lethargy or despondency.
All of these studies are inconsistent and, in some cases, contradictory. However, because SAD is likely due to a combination of various biological and physiological factors working together, different interpretations of its causes may be interconnected.
SAD and Your Eye Color
Lance Workman’s team found evidence suggesting that a person’s eye color may directly influence their sensitivity to SAD.
The group’s research utilized a sample of 175 students from two universities (one in southern Wales in a colder region and one in Cyprus in a subtropical region). They discovered that when compared in the seasonal pattern evaluation questionnaire, individuals with lighter or blue eyes scored significantly lower than those with darker or brown eyes. These results align with previous research indicating that individuals with brown or black eyes are significantly more likely to experience depression compared to those with blue eyes.
The reason eye color may make some people more susceptible to depression or mood changes could be related to the amount of light their eyes can process.
The retina is a part of the eyeball that contains light-sensitive cells. When light enters the eye, these cells activate nerve impulses that form visual images in our brain.
In 1995, scientists discovered that some retinal cells, rather than creating images, only send information about light levels from the back of the eye to the hypothalamus of the brain. The hypothalamus is a crucial part of the brain that releases hormones (such as oxytocin) that regulate temperature cycles, feelings of hunger, and sleep.
As the levels of blue and green light increase in the hypothalamus, melatonin production decreases. Lighter-pigmented eyes (blue or gray) are more sensitive to light. This means they do not need to absorb as much light as brown or dark eyes before this information reaches the retinal cells.
Thus, individuals with lighter eyes produce less melatonin in the fall and winter. This mechanism may provide those with lighter eyes some resilience against Seasonal Affective Disorder (although a smaller proportion may still experience SAD).
So far, there are two hypotheses proposed to explain why blue eyes tend to appear only in Western communities that live further from the equator:
- Firstly, it may be perceived as more attractive to the opposite sex, thus providing a reproductive advantage.
- Secondly, blue eyes may be a side effect of the same mutation that leads to lighter skin. This mutation developed because it helps the body produce more vitamin D from the sun’s ultraviolet rays in areas of the world that receive less radiation, especially during winter.
However, since the blue-eyed individuals in the study reported lower levels of SAD compared to brown-eyed individuals, this mutation may have occurred as an adaptation “against SAD” due to the significant changes in light exposure that our prehistoric ancestors experienced when they migrated to northern latitudes.
Of course, eye color is not the only factor at play here. People who spend too much time indoors are also susceptible to both winter blues and full-blown SAD. Fortunately for those affected by SAD, simply going outside for regular walks, especially on sunny days, can help improve their mood.
If that does not work, then “light therapy,” which involves sitting in front of a lightbox for an hour each day, can also be beneficial. Lance Workman noted that individuals using these methods (whether they have brown or blue eyes) consistently report a significant improvement. However, those with SAD should consult their general practitioner, particularly if their symptoms do not improve or if their condition becomes difficult to manage.
All that remains of hunter-gatherer societies in the Middle Stone Age in Europe investigated so far shows a genetic sign for lighter-colored eyes, in cases where hunter-gatherers in Western and Central Europe had darker skin.
Later additions to the European gene pool, such as Neolithic farmers from Anatolia and Bronze Age/Copper Age Yamnaya herders (possibly the original Indo-European population) from the northern Black Sea region, appear to have a much higher prevalence of dark eye color alleles and alleles that produce lighter skin compared to the original European population.
The genetics and inheritance of eye color in humans is very complex. To date, 16 genes have been identified that are related to eye color inheritance. Some of the eye color genes include OCA2 and HERC2. Previously, it was thought that blue eye color was a simple recessive trait, which has been proven to be inaccurate. The inheritance of eye color is so complex that virtually any combination of eye colors between parents and children can occur.
