Gender and eye color influence the risk for the development of seasonal affected disorder, say 2 new studies. The explanations for why are fascinating, too.
Seasonal affective disorder is a kind of depression occurring during the winter only in countries far away from the equator. The psychiatric condition, Seasonal Affective Disorder or “SAD” occurs in the fall and winter. As a type of depression, the symptoms are similar to other depressive disorders. Acute sadness and feelings of hopelessness affect about 5 percent of the American population. Women tend to be at higher risk.
SAD is sometimes simply called winter depression. Mornings start later as winter approaches. Evenings also begin earlier. There is less sunlight in each day. SAD is most likely caused only by a lack of sunlight. The cold temperatures do not appear to contribute to the condition.
About 80% of those affected are women. Researchers have found no correlation with social and lifestyle factors, which suggests that there could be biological gender specific issues.
The depressive symptoms tend to build up slowly when the days are getting shorter. Gradually the SAD symptoms subside in the spring, when there is more sunlight each day.
Things to know about SAD:
- There was no clinical name for SAD until the early 80s.
- SAD symptoms are very similar to the symptoms of depression.
- The most common symptoms are social withdrawal, lethargy and low mood.
- Scientific literature first mentions the symptoms of SAD in 1845 even though it was not given a name until almost 140 years later.
Our circadian rhythms are affected by seasonal changes in the amount of sunlight each day. This is also called our “internal biological clocks”. 4-6 % of Americans suffer from SAD. They are more likely to be young adults who first noticed symptoms when they were between 20 and 30 years old. SAD is far more common the further north you travel. It is 7 times less common in Florida than in Washington State.
Causes of SAD
The experts continue to be unsure about the causes of SAD. Studies are pointing to the following areas:
Unbalanced Melatonin and Low Serotonin Levels
Your sleep patterns and moods are influenced by your melatonin levels. Reduced sunlight exposure in the shorter days of winter seems to disrupt melatonin balance. Serotonin levels are low in those suffering with SAD during the winter months as well.
Your circadian rhythm is your body’s internal clock. It is supposed to tell you when to be awake and when to be asleep. With less sunlight during the winter your circadian rhythm can be disrupted, which causes depressive symptoms.
The hypothalamus is a portion of your brain that controls your appetite, mood and sleep. Since sunlight stimulates the hypothalamus this can impact how you feel. Also, the production of the neurotransmitter serotonin that impacts your mood, could be affected by low sunlight levels.
Previously Known Risk Factors
Previous studies have shown a short list of risk factors.
- Gender – Women are more likely than men to suffer from SAD. If men do have SAD they seem to be prone to more severe symptoms.
- Geography – Being further from the equator equates to a higher risk for SAD. The places that have the shortest winter days are most likely to have higher incidents of SAD.
- Genetics – Anyone with any close relative with SAD has a greater risk.
- History of Depression – A history of other types of depression makes it more likely that you will suffer from SAD.
The most recent research has confirmed that women are more likely to suffer, and adds a fascinating consideration. Apparently eye color is a risk factor for SAD. These new studies are offering an intriguing explanation for why gender and eye color are contributing risk factors.
The Research Team’s Findings
The findings were presented to the attendees at the 2018 conference of the British Psychological Society, held in Nottingham, United Kingdom. Lance Workman presented the findings. He is a University of South Wales professor.
Blue Eyes Keep the Blues Away
Prof. Workman presented his first study which he titled ‘Blue eyes keep the blues away: the relationship between SAD, lateralized emotions, and eye color’. In this study he surveyed 175 students from the Girne American University and the University of South Wales.
The questionnaires revealed that brown eyed participants experience mood shifts significantly more often when compared to the blue-eyed participants.
Prof. Lance Workman explains, “We know that light entering the brain causes a decrease in levels of melatonin. As blue eyes allow more light into the brain, it may be that this leads to a greater reduction in melatonin during the day and this is why people with lighter eyes are less prone to SAD. This, may be taken as suggestive that the blue eye mutation was selected as a protective factor from SAD as sub-populations of humans migrated to northern latitudes.”
People with SAD Use the Right Side of the Brain
Participants with SAD took part in a test that examined the response of their two brain hemispheres. This was tested when they tried to recognize emotional expressions. The test showed that those suffering with SAD had a tendency to use the left visual field.
Prof. Workman explained that, “This tendency to use the left visual field and right side of the brain for identifying facial expressions is present in the general population, whether they [live with] SAD or not.
But, people who [have] more conventional forms of depression generally lose this right hemisphere advantage.”
In those suffering from SAD, this left visual field utilization advantage was increased. This confirms that SAD stems from different causes than other types of depression.
Why Women Are at Higher Risk
The other study that was presented at the conference surveyed a sample of 2,031 people. 8 % had the chronic form of SAD, and 21 % had the milder type.
During their reproductive years, women are at a particularly high risk. They are 40 % more likely to suffer from SAD than men are. Prof. Workman ventured another guess using an evolutionary explanation. The speculation is that SAD is just an energy-saving mechanism that has gone wrong.
He supports this speculation by adding that those who suffer from SAD also crave carbs, and gain weight over the winter. He suggested that this could have helped our ancestors cope with cold.
When eye color, gender, genetics and geography are combined with a history of depression the risk for developing SAD is greater. There are some treatments available, but this is an area that warrants more study. SAD clearly has different causes than other forms of depression so treating it differently does make sense. Light therapy helps some, but until the underlying cause is found it is likely that brown-eyed woman in northern climates may need to seek relief in the way of a winter holiday closer to the equator.
Mental Health America
American Family Physician
University of Virginia
The British Psychological Soicety