Seasonal affective disorder (abbreviation: ATS) is a predominantly depressive disorder that occurs in the late fall or winter months. In spring and summer, the symptoms of depression disappear. Scientists believe that a possible cause of bad mood lies in low levels of serotonin. However, other factors - genes, stress and hormones - can also influence the development of depression.
Hypothesis No. 1: little light and a lot of melatonin
When it gets dark in the evening and less light falls into the eyes, the pineal gland releases the hormone melatonin. It reduces anxiety, prepares for sleep and improves falling asleep. In winter, the light intensity is lower, so more melatonin is released during the day.
In patients with "winter depression," the flow of information from the visual cells of the eye to the brain is disrupted.
The visual cells of patients are less sensitive to light. If a person lacks light, nerve cells produce more sleep hormone. The "overproduction" of melatonin is one of the causes of severe fatigue and depressive symptoms.
Hypothesis No. 2: a lot of melatonin and a little serotonin
Serotonin is required for the production of melatonin. If the concentration of melatonin increases, then, consequently, the level of serotonin decreases. Serotonin is a chemical that stabilizes a person’s mood. Antidepressants that increase serotonin levels in the brain can reduce winter depression.
If the brain lacks serotonin, it tries to compensate for the deficiency by other means. The desire for sweet foods is found in many people in the winter.
Sugar and some of the ingredients in chocolate help restore the concentration of serotonin in the brain cells.
Researchers scanned 11 patients with ATS and 23 healthy people using positron emission tomography. Scientists were able to identify significant differences in the amount of serotonin transporter (SERT) in summer and winter. Patients with seasonal affective disorder showed a higher level of SERT in the winter months. Therefore, they observed less serotonin in the winter.
Sunlight keeps SERT levels low. However, as nights get longer, SERT levels rise. As a result, the concentration of serotonin is reduced. Patients with seasonal depression have an average SERT level of 5% higher in winter than in summer.
Hypothesis No. 3: disturbed biological rhythms
The human body follows a biological rhythm: the sleep-wake cycle is regulated by the light that enters the eyes.
In people with winter depression, the "biological clock" appears to be impaired. Therefore, a lot of melatonin is released both in the morning and at night.
Will “artificial” light help get rid of depression?
A new study shows that the gold standard in treating seasonal affective disorder - light therapy - is ineffective. Cognitive-behavioral therapy is more effective, according to studies published in the American Journal of Psychiatry.
Researchers at the University of Vermont found that light therapy was effective in acute episodes of seasonal affective disorder. However, special cognitive-behavioral therapy adapted to ATS was significantly better at preventing recurrence of the disease.
In a French study, 177 subjects were treated for 6 weeks with light phototherapy. Daily exposure to bright artificial light of certain wavelengths did not help to get rid of depression.
With the help of special cognitive-behavioral therapy, which cast doubt on negative thoughts about the “sad” winter months, patients got rid of ATS.
More recent studies of seasonal affective disorder found that not all people are prone to mood changes. Scientists suggest that the reason for poor mood in healthy people can not be a change in the length of the day or night. About 5-7% are susceptible to ATS, while other people feel sad - nothing more than fiction and self-hypnosis.
Modern researchers believe that the prevalence of bad mood in winter is clearly exaggerated.
