What is seasonal affective disorder?

Also known as seasonal affective disorder or SAD. It is a type of depression that follows a seasonal pattern.

The most common form is winter depression, which is characterised by a worsening of symptoms, especially depression and lethargy, in autumn and winter, followed by an improvement in spring and summer.

There are also spring and summer depressions that occur regularly every year, not just in winter, with depressive symptoms worsening in spring and summer and improving slightly in autumn. 83% of patients are women.


In the case of winter depression, the lack of sunlight and sunshine hours is thought to trigger a biochemical response that leads to a lack of energy, decreased activity, sadness, overeating, and over-sleeping; in spring depression, it’s thought to be due to the disruption of circadian rhythms and temperature changes caused by sudden changes in sunlight; and in summer depression, it’s thought to be due to the heat of the summer.

The hypothalamus, a part of the brain that helps us adapt to external changes, is impaired in people with seasonal depression. It is not yet known exactly what causes winter depression, but it is thought that there may be a connection between the eyes and the hypothalamus, while in spring and summer depression, there may be a disruption in the neuroanatomical pathways involved in the body’s response to heat.


Symptoms are characterised by feelings of lethargy during the depressive period. People with winter depression tend to eat a lot and crave sweets and sugars during the depression, while those with spring and summer depression tend to have a decreased appetite and weight loss.

People with winter depression also feel physically drained during depression, whereas people with summer depression feel agitated. In particular, people with summer depression have more suicidal ideation and are more likely to self-harm than people with winter depression. In some cases, people regularly experience symptoms of depression in both the summer and winter seasons.


Treatments include phototherapy, which involves exposure to strong light for a certain period of time each day, and cooling the environment. Medications include antidepressants, and psychotherapy can also be effective.

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