What causes it?
The exact cause of SAD is unknown, but it is linked with changes in the secretion of various brain chemicals as the days draw in and exposure to natural sunlight is reduced. These changes may involve an increased sensitivity to a natural sedative hormone, melatonin, which is produced by the pineal gland in the brain. During daylight hours, little melatonin is made so you feel energetic and alert. During darkness, larger quantities of melatonin are made so you naturally slow down and tend to feel more sleepy. As days shorten and nights lengthen during late autumn and early winter, overall melatonin secretion tends to go up. This cannot be the sole cause of SAD however, as symptoms do not consistently respond to drug treatment designed to suppress the secretion of melatonin hormone. Seasonal variations in the secretion of the neurotransmitter, serotonin, thyroid stimulating hormone (TSH), and the get-up-and-go hormone, adrenaline, may also be involved. Recently a genetic link between the presence of a particular gene, DRD4, has also been associated with seasonal patterns of weight gain and binge eating.

Treatment for SAD
As SAD is linked with lack of sunlight, symptoms are often improved by using a special light box that emits bright, cool white fluorescent light (2500 lux) similar to natural daylight (so-called natural daylight bulbs are not strong enough to help, however). The box can be set up near your bed and timed to come on with increasing brightness before you wake to simulate a natural dawn. This fools the pineal gland into thinking spring has arrived, so melatonin secretion goes down, your mood increases and sleepiness and lethargy improve - usually within a week or two. Treatment is best started a month or so before your symptoms usually develop, which for some people is as early as October. Another way in which bright light therapy works is by raising levels of the adrenal hormone, cortisol. Using a light box to simulate a natural dawn has been shown to significantly increase total cortisol production during the first 45 mins after waking and to increase wakefulness in people without SAD - the next step is to see if the same results occur in people with winter depression. Light box hire schemes are available so you can see if bright light therapy works for you before investing in buying one.

St John's Wort (Hypericum perforatum) is an effective herbal treatment for mild to moderate depression and helps some people with SAD. One field trial found that it was just as effective when used alone as when combined with light box therapy. However, rarely, some people have developed excessive sensitivity to light when taking St John's Wort, leading to a photosensitivity rash, so it may not be a good idea to combine treatment with light box therapy - seek advice from a medical herbalist if you want to do this.

In more severe cases of SAD, antidepressant drugs may be needed. Traditional antidepressants, known as tricyclics, tend not to help people with SAD as they have side effects of sleepiness and lethargy that make symptoms worse. The newer, non-sedative antidepressants (SSRIs, which work by raising levels of serotonin) can be effective in alleviating depressive symptoms, however, and can be used together with light therapy.

The excessive sleepiness associated with SAD may respond to treatment with the new stimulant drug, modafinil, which helps to promote wakefulness. A small, recently published study involving just 13 patients found that modafinil significantly improved winter depression with two out of three people showing a response, which requires further investigation.

How to help yourself beat SAD
Self help approaches to SAD include keeping warm, getting up early rather than lying in bed (which will increase feelings of lethargy), getting out into the open air for exercise as much as possible, and eating little and often during the day. It may help to eat a low-glycemic diet concentrating on wholegrain cereals, root vegetables, legumes, oily fish and cheese - the later two foodstuffs contain tryptophan, a substance needed to make serotonin in the brain. Try to avoid overeating, however, as research suggests people with SAD selectively eat more carbohydrates during the winter months, and that weight gain is linked with eating chocolate and sweets when feeling depressed, anxious or lonely.

For an information pack about SAD, send a cheque for £5 to: The SAD Association, PO Box 989, Steyning, West Sussex BN44 3HG, or request one via the Sada website - which also provides further information.