With the onset of the winter months, the associated lack of sunlight and the shortening of daylight hours can often have an adverse effect on our health. In fact, it is estimated that, every winter, half a million people in Britain suffer symptoms ranging from sleep problems, lethargy, overeating, depression, social problems, anxiety and mood changes. The clinical name for this illness is Seasonal Affective Disorder (SAD). The severity of the symptoms of SAD can vary from those patients who are unable to function normally without continuous medical treatment, to those with sub-syndromal SAD - sometimes known as the 'winter blues' - who are likely to experience physical symptoms of SAD but not the symptoms of depression. A diagnosis of SAD can be given when the patient has suffered for three or more consecutive years with recurrent winter symptoms. Causes of SAD

SAD sufferers have been found to have an altered brain biochemistry. For many years, increases in levels of melatonin, which is stimulated by the amount of light entering our eyes, were thought to be closely related to the disorder. However, studies comparing melatonin levels in those with the disorder and those who do not suffer from SAD have shown that it is unlikely to be the sole cause of the problem. The greatest impact is, in fact, caused when the SAD sufferer's biochemical-producing cycle becomes out of synchronisation with the rest of the body.

Studies in Canada have shown that the prevalence of SAD is related to higher (e.g. more northern) latitudes rather than with hours of sunlight, barometric pressure or temperature. Therefore, it can be assumed that it is the length of the day during winter that is a more important factor in the symptoms of SAD than local weather conditions, such as the amount of sunlight. This has been found to be consistent with SAD patients who, for example, do not become clinically depressed in bad weather during the summer nor experience normal mood patterns during spells of good weather in the winter.

Treatments

Light therapy has proven to be an effective treatment in 85% of cases of SAD. During the treatment, the patient will be exposed to very bright light emitted from a light box for between 30 minutes and four hours a day. Ordinary domestic lighting is not bright enough to provide sufficient relief. It is important that the light box is used regularly for the full benefits to be felt.

The fact that light is an effective treatment for SAD has been a stumbling block for the recognition of the disorder. In America in the 1980s, Dr Norman Rosenthal, who suffered from SAD himself, wrote a short article about the disorder in the Washington Post, which received a surprisingly good response. Five years on, and Dr Rosenthal estimated that between 6% and 10% of Americans suffer from SAD, and that light boxes can effectively treat 80% of cases. But it was not until 1995 that the scientific community accepted the disorder and the light-treatment therapy. It was suggested that, because the treatment for SAD is light therapy rather than drug therapy, many people dismissed it as just having a placebo effect.

Other SAD-relieving devices include a light visor and a dawn simulator that comes on in the morning in the last few hours of darkness to gradually brighten the room. Going outside into natural daylight as often as possible, particularly when the day is at its brightest, can also help, but this is insufficient in isolation. In some cases, antidepressants can be prescribed, although some are counterproductive as they can often cause the main symptoms of the disorder, such as sleepiness and lethargy.

The seasonal change in spring and autumn can have a temporary unsettling effect on those suffering from SAD, which is due to the body readjusting to the difference in daylight. Those with severe cases of SAD are advised to carry out more stressful tasks during the summer months when they feel more energetic, saving the less stressful tasks for the winter when their energy levels are lower.

For more information, e-mail health@metoffice.gov.uk.

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