Seasonal affective disorder and the power of sunlight

Seasonal affective disorder and the power of sunlight

Here in the Northern Hemisphere, summer has finally arrived. For those of us who suffer from depression during those bleak winter months, summer is a welcome respite as our moods are often lifted and we naturally gravitate to the outdoors, eager to feel the sun’s rays on our skin once again.

Seasonal affective disorder (SAD) is a common psychiatric condition whereby an individual experiences mood disorders, such as depression or anxiety, during the winter months. Afflicting millions of Americans, the most recent statistics suggest that about 7.1% of the US population are affected by SAD and that it occurs more often in women than in men (National Institute of Mental Health, 2022). It is also more noticeable in areas north of the equator that have shorter daylight hours during the winter months, such as in Alaska or New England. In most cases SAD is cyclical, beginning in the late fall to early winter months before subsiding in the spring to summer months, once the days get longer.

It is widely believed that one of the potential causes of psychiatric disorders, such as SAD, is due to a disruption in the serotonergic system. Commonly referred to as the “happy” chemical, serotonin plays an essential role in the body, stabilizing mood, aiding in sleep, facilitating digestion, and a host of other bodily functions.  As such serotonin, has been used in the treatment of depression for many years (Gupta et al., 2013).

Located in three different areas of the body: the central nervous system, the gastrointestinal lining (the largest producer of serotonin), and the blood platelets, this serotonin is synthesized from tryptophan, an essential amino acid found in foods such as turkey, milk, and bananas (Sansone & Sansone, 2013).

But, did you know that sunlight may also play a fundamental role in the production of serotonin? A potentially potent antidote to SAD, the sun offers multifaceted benefits with some data suggesting an association between its powerful rays and meaningful serotonin production. While the relationship between the sun and serotonin may be due to a variety of complex variables — including the effects of the suns rays entering the body via the retina of our eye and stimulating our central nervous system (CNS) — we also know that the skin has its own inherent serotonergic system, suggesting that it may be capable of producing this happy chemical on its own (Gambichler et al., 2002). While the data is still preliminary, this may explain our innate desire for sunbathing as soon as summer rolls around.

Historically, the sun has been a crucial part of human existence, from ancient Greek mythology and sun worshipping in ancient Egypt to modern history with Louis XIV of France referring to himself as the “Sun King”. Medical practitioners throughout the ages would embrace the sunlight as a practical and holistic way to manage illness, a treatment that later came to be known as heliotherapy. In fact, the first scientific documentation of this practice came from Danish Nobel prize winner Niels Robert Finsen for his successful treatment of skin conditions (Alpert, 2015). Many physicians and healthcare providers followed suit, opening sunbathing clinics across the globe to treat a myriad of other conditions including skeletal and pulmonary (particularly tuberculosis) diseases.

Ultimately, while we know that too much sun can indeed be a cause for concern, moderate sun exposure especially during the early morning hours or late afternoon might be a pleasant option to consider for those of us feeling the remains of the winter blues.



Alpert, J. S. (2015). The Jeremiah Metzger lecture: Jeremiah Metzger and the era of heliotherapy. Transactions of the American Clinical and Climatological Association126, 219.

Gambichler, T., Bader, A., Vojvodic, M., Bechara, F. G., Sauermann, K., Altmeyer, P., & Hoffmann, K. (2002). Impact of UVA exposure on psychological parameters and circulating serotonin and melatonin. BMC dermatology2(1), 1-7.

Gupta, A., Sharma, P. K., Garg, V. K., Singh, A. K., & Mondal, S. C. (2013). Role of serotonin in seasonal affective disorder. Eur Rev Med Pharmacol Sci17(1), 49-55.

Sansone, R. A., & Sansone, L. A. (2013). Sunshine, serotonin, and skin: a partial explanation for seasonal patterns in psychopathology?. Innovations in clinical neuroscience10(7-8), 20.

U.S. Department of Health and Human Services, National Institute of Mental Health. (Updated 2022). Seasonal affective disorder. (NIH Publication No. 20-MH-8138). Retrieved from



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