Seasonal Affective Disorder (SAD) is a type of depression which occurs periodically, with the onset of symptoms in winter months and full recovery during the spring and summer. That is why it is also called winter blues or winter depression. The usual symptoms experienced by SAD patients are: bad mood, increased hunger and weight, low energy, fatigue, sleeplessness, irritability, concentration problems, etc.


There are numerous substances in the brain tissue that enable the communication between nerve cells. These substances are called neurotransmitters, and the most important of them include serotonin, norepinephrine , and dopamine. The disturbances in levels of neurotransmitters can induce mental disorders such as SAD.

The Role of Serotonin

The clue that serotonin might be involved in the development of SAD was derived from the scientific evidence that serotonin levels in the brain tissue vary seasonally in healthy individuals. That was confirmed in animal as well as in human studies. The lowest levels of serotonin in the brain tissue were found in January and December, and many studies have been conducted with the aim to investigate the role of serotonin in the development of winter depression. Tryptophan is an important amino acid in our body and it is also a precursor of serotonin. Decreased levels of tryptophan were measured in persons suffering from SAD, especially during winter months. Serotonin is also involved in the metabolism of melatonin – a very important substance in our brain which controls circadian rhythm and regulates sleeping.

Many symptoms of SAD are considered the result of serotonin deficiency, for example: sugar cravings, anxiety, disturbed sleep cycle, bad mood, and the feeling of guilt.

Ways to Increase Serotonin Levels

The knowledge about serotonin disturbances in persons with SAD has contributed to the development of therapeutics that can modify the serotonin levels in the brain tissue. Selective Serotonin Reuptake Inhibitors (SSRIs) as well as Serotonin and Norepinephrin Reuptake Inhibitors (SNRIs) are antidepressant drugs that increase the amount of serotonin in the brain, thus improving the symptoms of winter blues.

Research conducted on rats proved that the increased exposure to sunlight leads to increased serotonin levels. That is why light therapy greatly improves the symptoms of SAD, and it is the most commonly used treatment option today. Also, several studies have shown beneficial effect of massage on serotonin levels. In one study, the massage increased serotonin levels by 30%. Running, aerobic, walking, swimming, and all other forms of physical activity are well known to increase serotonin levels. Positive thinking, yoga, and happy events are also the things that boost serotonin production.

In conclusion, serotonin is proven to be a very important factor in depressive disorders, and the disturbances in serotonin levels undoubtedly contribute to the development of SAD.  Persons suffering from this disorder should engage in all of the above activities as much as possible in order to improve their condition. The light therapy applied via light boxes (panels that emit the light of certain wavelength) is shown to be the most effective treatment option.


Gupta, A., Sharma, P.K., Garg, V.K., Singh, A.K., Mondal, S.C. Role of serotonin in seasonal affective disorder. Eur Rev Med Pharmacol Sci. 2013 Jan;17(1):49-55.

Schloss, P., Williams, D.C. (1998). The serotonin transporter: a primary target for antidepressant drugs. J Psychopharmacol. 12: 115-121.

Michel, K., Zeller, F., Langer, R., Nekarda, H., Kruger, D., Dover, T.J., Brady, C.A., Barnes, N.M., Schemann, M. (2005). Serotonin excites neurons in the human submucous plexus via 5-HT3 receptors. Gastroenterology. 128: 1317-1326.

Tyce, G.M. (1999). Origin and metabolism of serotonin. J Cardiovasc Pharm 16: S1-S7.

Lambert, G.W., Reid, C., Kaye, D.M., Jennings, G.L., Esler, M.D. (2002). Effect of sunlight and season on serotonin turnover in the brain. Lancet 360: 1840-1842.