What is seasonal affective disorder (SAD)?

Seasonal affective disorder (SAD) is a form of depression that people experience at a particular time of year or during a particular season. Most of us are affected by the change in seasons – it is normal to feel more cheerful and energetic when the sun is shining and the days are longer in summer, or to eat more or sleep longer in winter. However, if you experience SAD, the change in seasons will have a much greater effect on your mood and energy levels, and lead to symptoms of depression that have a significant impact on your day-to-day life.

Most people experience SAD during the winter. However, some people experience SAD in reverse, with depressive symptoms occurring in summer.

“For years I suffered from depression. It started in the autumn, as the evenings drew in. By Christmas, I would be so low that I could barely get out of bed…One year, I felt so bad that I went to bed on Christmas Eve and refused to move.”

You are more likely to experience SAD if you live in a country where there are significant changes to daylight, temperature and weather between seasons. Thus, SAD is more common in Scandinavia, Europe, North America, North Asia, and in southern parts of Australia and South America. In northern Europe, it is estimated that about one in ten people experience some symptoms of SAD.

It is extremely rare to find people with symptoms of SAD living near the equator, where daylight hours are long and bright all year round.

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