Depressive disorders are starting to be the greatest burden of modern society. According to most recent data provided by the World Health Organization, 350 million people suffer from depression, and it is considered the leading cause of disability around the world. Seasonal Affective Disorder (SAD), also called winter blues or winter depression, is the form of depression which occurs mostly in cold regions with the lack of sunlight or during the winter season.

It is well-known that the occurrence of winter blues is related to the deficiency of exposure to sunlight, which is why the light therapy plays an important role in the treatment of affected individuals, and the lightboxes are usually used for that purpose. Besides that, antidepressant drugs are also used in more severe forms of the disease.

The Role of Melatonin in Regulating the Circadian Rhythm

Recently, the role of melatonin, a naturally occurring hormone in the brain tissue, is linked to the development and severity of SAD symptoms. Melatonin has a great impact on the regulation of our circadian rhythm (the internal process in the brain that dictates the changes in bodily functions during the 24 hours of a day). It is noticed that the production of melatonin varies during the day. The highest levels are in the evening and during the night, which suggests that melatonin helps to maintain sleep. During the morning hours, the melatonin levels decrease, thus inducing awakening.

Melatonin Levels and Sunlight

Scientists have been searching for the factor which causes the daily changes in melatonin levels. The researchers from Seattle Swedish Medical Centre, Seattle, WA, have noticed that the persons living in the northern latitude have the greatest risk of developing SAD. Besides that, the melatonin levels in those persons are shown to be higher and poorly regulated, which suggests the impact of sunlight on melatonin secretion. Therefore, the disturbances in melatonin secretion as a consequence of the lack of sunlight might represent the cause of SAD. One of the studies dealing with the effects of lightboxes on melatonin levels has confirmed these findings. Namely, the evening course of light therapy delayed the normal increase in melatonin levels by 2.8 hours, while the morning course prolonged the normally occurring decreased levels of melatonin by 2.65 hours.

Melatonin for The Treatment of SAD

Alfred Lewy and his team from Oregon Health and Science University investigated the possibility of using melatonin in the treatment of SAD. The study divided 68 patients suffering from SAD into two groups receiving melatonin capsules or placebo in the morning or in the evening for 4 years. They have found that most of the patients receiving evening doses of melatonin experienced improvement of the symptoms. The key is that evening dose of melatonin enables good night sleep and encourages the restoration of normal melatonin secretion cycle.

The whole concept of circadian rhythm importance for the proper functioning of the nervous system has not received enough attention. Although the exact mechanism of action of melatonin is not yet discovered, its role in the development and evolution of winter depression is supported by scientific evidence, and the upcoming treatment options for this disorder may actually involve melatonin supplementation.


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Lewy, A.J., Rough, J.N., Songer, J.B., Mishra, N., Yuhas, K., Emens, J.S. (2007). The phase shift hypothesis for the circadian component of winter depression. Dialogues Clin Neurosci. 9(3):291-300.

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Lewy, A.J., Lefler, B.J., Emens, J.S., Bauer, V.K. (2006). The circadian basis of winter depression. Proc Natl Acad Sci U S A. 103(19):7414-9.

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