Seasonal affective disorder (SAD) is a type of seasonal depression characterized by major depressive episodes in the fall/winter and remissions in spring/summer. The symptoms include persistent low mood, lack of interest, irritability, lack of energy, irritability, longer hours of sleep, withdrawal from social situations, and craving for carbohydrates.
It is estimated that 1-10% of the population is affected by seasonal affective disorder, with a predominance in northern latitudes where there is less light during fall and winter. It is also more common in women than men with a predominance in younger individuals .
How Is Seasonal Affective Disorder Diagnosed?
To differentiate between seasonal affective disorder and other depressive disorders, individuals are assessed using the following criteria:
1- A history of a minimum of two chronological years of fall/winter depressive episodes and remission in the spring or summer.
2- Absence a history of depression associated with other depressive disorders that can also manifest seasonal affective disorder such as hypersomnia, increased appetite, and fatigue.
What Are the Causes of Seasonal Affective Disorder?
Although it is clear that there is an association between seasonal affective disorder and seasons, the mechanisms that cause this type of depression are not well known and several hypotheses that gravitate around the lack of sufficient light exposure during fall and winter, have been formulated:
1- Melatonin Level
Melatonin is a hormone that is secreted by the pineal gland during the night to regulate the circadian rhythm. Its activity is mediated by the suprachiasmatic nucleus, a region located in the hypothalamus. Due to the reduction in exposure to blue light during fall and winter, there is an increase in melatonin secretion which promotes a state of sleepiness and tiredness .
2- Serotonin Level
Serotonin, also known as 5-hydroxytryptamine or 5-HT, is a neurotransmitter that modulates mood, cognition, learning, memory, depression, anxiety, and social phobia. Although studies expressed concerns regarding the role of serotonin in seasonal affective disorder, others have shown that the level of serotonin was lowest in winter which may affect the mood in individuals who are less exposed to light .
3- Circadian Clock
The circadian clock is our 24-hour clock associated with physical, mental, and behavioral changes that happen within the day-night cycle. Several studies have reported anomalies in circadian clockwork in patients with seasonal affective disorder, while another study reported a link between some genes involved in the circadian clock (e.g., Per2, Arntl, and Npas2) and seasonal affective disorder .
The involvement of genetic inheritance in seasonal affective disorder has been reported using twin studies where it was shown that two genetic variants involved in the serotonin pathway are involved in seasonal affective disorder .
What Is the Treatment for Seasonal Affective Disorder?
1- Lifestyle Changes
As a lack of light appears to be an important factor in the etiology of seasonal affective disorder, getting enough natural sunlight exposure can be a considerable help. Regular outdoor exercising (preferably) can also lower stress and prevent depression.
2- Light Therapy
This therapy involves the use of a lightbox with the aim of reducing the production of melatonin to prevent sleepiness and tiredness and inducing the production of serotonin to modulate mood changes associated with anxiety and depression .
3- Cognitive Behavioral Therapy (CBT)
As the symptoms of seasonal affective disorder include persistent low mood, lack of interest, irritability, lack of energy, irritability, longer hours of sleep, withdrawal from social situations, and craving for carbohydrates, cognitive behavioral therapy is used to improve cognitive disorders, behaviors, and develop coping strategies.
4- Psychodynamic Psychotherapy
This type of psychotherapy can be complementary to cognitive behavioral therapy. As patients may have low self-esteem and lack of confidence, they can discuss past experiences with a professional to alleviate associated feelings and emotions.
Second-generation antidepressants such as Selective Serotonin Reuptake Inhibitors (SSRI), particularly fluoxetine (Prozac), are used for the treatment of patients with seasonal affective disorder .
Although the mechanisms underlying the causes of seasonal affective disorder are based on theories, and therefore, not well-known, early diagnosis and prevention of this disorder in patients is extremely important.
Treatment using light therapy resulted in mixed evidence and its application can lead to side effects including increased tiredness, irritability, headaches, blurred vision, and sleeping problems. Therefore, it is essential to clarify the therapeutic effect of light therapy to avoid incomplete treatment of patients who are in distress and need urgent treatment for their suffering.
Finally, seasonal affective disorder is classified as a major depressive disorder that can become extremely severe with consequences that can potentially develop into suicidal thoughts particularly during the gloomy weather of fall and winter in countries that are less exposed to sunlight during those periods of the year.
 Neumeister, A., Pirker, W., Willeit, M., Praschak-Rieder, N., Asenbaum, S., Brücke, T. and Kasper, S., 2000. Seasonal variation of availability of serotonin transporter binding sites in healthy female subjects as measured by [123I]-2β-carbomethoxy-3β-(4-iodophenyl) tropane and single photon emission computed tomography. Biological Psychiatry, 47(2), pp.158-160.
 Partonen, T., Treutlein, J., Alpman, A., Frank, J., Johansson, C., Depner, M., Aron, L., Rietschel, M., Wellek, S., Soronen, P. and Paunio, T., 2007. Three circadian clock genes Per2, Arntl, and Npas2 contribute to winter depression. Annals of medicine, 39(3), pp.229-238.
 Rosenthal, N.E., 1984. Seasonal affective disorder: a description of the syndrome and preliminary findings with light therapy. US Department of Health and Human Services, National Institutes of Health.