It is thought that SAD affects around 2 million people in the UK and more than 12 million people across Northern Europe. It can affect people of any age, including children. The symptoms are most likely to appear in people aged between 18 and 30.
In people with milder depressive symptoms, the condition is often referred to as "winter blues".
The exact cause of SAD is not fully understood at present. However, it is believed to be tied to a reduced exposure to sunlight during the autumn and winter months. Research has shown that sunlight can affect some of the brain's chemicals and hormones, but - at present - it is not clear what this effect is. One theory is that light stimulates a part of the brain called the hypothalamus which controls mood, appetite and sleep, which can affect how you feel.
In SAD sufferers, the combination of a lack of sunlight and a problem with certain brain chemicals prevents the hypothalamus working from properly. The lack of light is thought to affect the production of the melatonin and serotonin, as well as affecting the body's internal clock (circadian rhythm), which regulates important biological processes throughout the day.
As with other types of depression, two of the main symptoms of SAD are mood swings and a generalised sensation of apathy. Other symptoms include a noticeable decrease in activity and sleeping more. The condition is, at times, called 'winter depression', due to the fact that it is at that time of year when symptoms typically manifest themselves and are more severe.
Often the onset of symptoms will start in autumn, as the days start to get shorter, and are most critical from December to February. In the majority of cases, the symptoms of SAD start to diminish in spring, before eventually disappearing.
Other symptoms include:
- Feeling irritable
- Feelings of despair
- Feelings of guilt and worthlessness
- Low self-esteem
- Feeling stressed or anxious
- A reduced sex drive
- Being less active than normal
- Feeling tired and sleep more than normal (hypersomnia)
- Feeling lethargic (lack energy)
- Finding it difficult to concentrate
- Having an increased appetite and eating more than usual (hyperphagia)
There are several types of treatment for Season Affective Disorder, amongst which the most common are: cognitive behavioural therapy; counselling and psychodynamic psychotherapy; the use of antidepressants, and - quite frequently - light therapy. If you present any of the symptoms described, visit your GP, who will be able to discern what the best form of treatment is for you. Although the condition can, at times, make day-to-day activities difficult, it can be overcome with the correct treatment.
Source: NHS choices: Seasonal Affective Disorder