Family doctor

Overview:

• Seasonal Affective Disorder is known as SAD for short
• It is a form of depression linked to autumn and winter time when sunshine hours are shorter
• Symptoms include low mood, weight gain, food cravings for carbohydrates and sleeping more
• SAD is believed to be caused by changes in serotonin levels in the brain
• The disorder is treated with light therapy or SSRI antidepressants

What is it?

Seasonal Affective Disorder (SAD) is a mood disorder linked to the autumn and winter months, and is sometimes known as the "winter blues".

It is a form of depression and mild symptoms affect up to 20 percent of the population; women seem to be more susceptible. It is believed about 4-6 percent of people are severely affected. The risk of SAD is highest in people with a history of depression.

It is more common in the Northern Hemisphere and in countries furthest away from the Equator, but is less common where is snows.

The syndrome, which was first recognised by the medical community in 1985, is thought to be brought on by the lack of sunshine hours and cooler temperatures during the winter time.

Researchers have found that bright light can change brain chemistry but the exact mechanism of these changes is still unknown.

It is currently believed that low serotonin levels in the brain are an important factor in seasonal depression.

Another theory suggests increases of melatonin during winter may explain seasonal depression, however there is minimal evidence to support this.

Changes in sleeping patterns have also been suggested as a possible explanation for SAD, but again, there is no strong evidence for this. However, it is possible that serotonin levels, melatonin secretion and sleeping patterns may all play a part.

The disorder may start between adolescence and the early 20s, and some people are affected all their lives.

Another type of seasonal affective disorder, known, as summer depression, is far less common and symptoms begin in spring and resolve during autumn.

What are the symptoms?

Symptoms include a low mood or depression which begins in autumn or winter.

Sufferers experience a lack of energy and interest in work or activities they once enjoyed. They may put on weight by eating more due to cravings for foods high in carbohydrates.

Some people may withdraw socially and sleep a lot more. They may also lose interest in sex.

Symptoms resolve with the onset of spring and summer.

There must be a pattern of seasonal depression over at least two years and for other explanations to be ruled out for SAD to be diagnosed as a medical problem.

The symptoms may be the same as clinical depression, which can occur at any time of the year, so it is important to seek professional help.

What can be done to help?

Light therapy (phototherapy) is the main treatment recommended by some doctors. This involves spending time under a special bright light in the morning or the evening. However, symptoms often return once the therapy is stopped.

The light must be at least 2500lux which is very bright given that a normal living room may only be 100lux. Bright sunlight provides about 10,000lux.

It is recommended that you spend between 15 and 45 minutes in the light, and allow it to reach your eyes. Patients should keep their eyes open and glance towards the light without staring directly into it. It is believed light therapy is effective when going through the eyes instead of the skin.

Light therapy should begin at 15 minutes per day, increasing up to 45 minutes a day.

Other treatments involve antidepressant drug therapy with a serotonin reuptake inhibitor (SSRI) such as Prozac as a first choice or an MAOI, such as moclobemide (Aurorix), if patients do not respond to Prozac.

One study comparing light therapy with Prozac found 70 percent of patients responded to the light therapy and 65 percent responded to treatment with Prozac.

Light therapy is recommended over Prozac because it works a lot quicker than the antidepressant which can take up to six weeks to be effective. The most common side effects reported so far from light therapy are eye strain and headaches.

People with retinal eye problems should check the safety of light therapy with their ophthalmologist.

A small study of the herbal remedy, St John's Wort, combined with light therapy was also found to be beneficial, but further studies are required before this treatment is routinely advised.

Taking a holiday in a warmer climate may also be helpful for seasonal depression.

Future trends

Full-spectrum fluorescent light therapy is being studied as a possible treatment for the disorder.

Other drug treatments may be shown to be effective.

Getting help

People who suspect they are suffering from SAD should talk to their doctor about their symptoms. The doctor will be able to rule out other conditions and recommend appropriate treatment.