SAD (Seasonal Affective Disorder) is a type of winter depression that affects an estimated 7% of the UK population every winter between September and April, in particular during December, January and February.
It is caused by a biochemical imbalance in the hypothalamus due to the shortening of daylight hours and the lack of sunlight in winter.
For many people SAD is a seriously disabling illness, preventing them from functioning normally without continuous medical treatment.For others, it is a mild but debilitating condition causing discomfort but not severe suffering.
We call this subsyndromal SAD or 'winter blues.' It is estimated that a further 17% of the UK population have this milder form of condition.