Some people like it. Some people loathe it. But certain things about winter are indisputable. The days are short and dark. You often get up and go out to work in the dark and get home in the dark. It’s possible not to see your house in daylight for what seems like ages.

If you’re at home during the day you often need the light on for most of the time. It’s constantly cold and you have to wrap up in layers of clothes to venture outside. Most of us start to wonder when we’ll ever see the sun again. Many of us feel thoroughly miserable.

Seasonal Affective Disorder (SAD) affects an estimated half a million people every winter between September and April, in particular during December, January and February. It is caused by a biochemical imbalance in a part of the brain known as the hypothalamus due to the shortening of daylight hours and the lack of sunlight in winter.

For many people SAD is seriously disabling, preventing them from functioning normally without treatment. For others, it is a mild but debilitating condition causing discomfort but not severe suffering. This is called sub-syndromal SAD or winter blues.

The symptoms of SAD usually recur regularly each winter, starting between September and November and continuing until March or April and a diagnosis can be made after three or more consecutive winters of symptoms, which include a number of the following: sleep problems; lethargy; over-eating; depression; social problems such as shunning contact with others; anxiety or irritability; loss of libido; and mood changes. In sub-syndromal SAD, symptoms such as tiredness, lethargy, sleep and eating problems occur, but anxiety is absent or mild.

SAD may begin at any time of life, but the main age of onset is between 18 and 30 years. It occurs throughout the northern and southern hemispheres, but is extremely rare in those living within 30 degrees of the equator, where daylight hours are long, constant and extremely bright.

What are the causes?
 
It has been suggested that the release of a brain chemical, melatonin, may be involved. Melatonin release is influenced by exposure to light and can exert an effect on several bodily rhythms. But research into this so far has been fairly inconclusive.
Doctors can prescribe medication, psychological therapy or bright light therapy.

Light therapy has been proved effective in up to 85 per cent of diagnosed cases. Ordinary light bulbs and fittings are not strong enough. Average domestic or office lighting emits an intensity of 200-500 lux but the minimum dose necessary to treat SAD is 2,500 lux. The intensity of a bright summer day can be 100,000 lux.

Light treatment should be used daily in the winter and dull periods in the summer starting in early autumn when the first symptoms appear. It consists of sitting two to three feet away from a specially designed light box, allowing the light to shine directly through the eyes.

The user can carry out normal activity such as reading, working, eating and knitting while stationary in front of the box. It is not necessary to stare at the light, although it has been proved safe. Treatment is usually effective within three or four days and the effect continues provided it is used every day. Tinted lenses or any device that blocks the light to the retina of the eye should not be worn,

You can join the SAD Association (Sada) and receive an information pack and a year’s membership with newsletters, list of contacts, telephone helpline, local groups, research and treatment updates, invitations to meetings, reduced rate books and other goods. Visit their website www.sada.org.uk/.