Seasonal affective disorder - Introduction

Seasonal affective disorder (SAD) is a type of depression that has a seasonal pattern. The episodes of depression tend to occur at the same time each year, usually during the winter.

As with other types of depression, two of the main symptoms of SAD are a low mood and a lack of interest in life. Other symptoms of SAD include:

• being less active than normal
• sleeping more

Read more about the symptoms of seasonal affective disorder.

'Winter depression'

SAD is sometimes known as 'winter depression' because the symptoms are more apparent and tend to be more severe at this time of the year.

The symptoms often begin in the autumn as the days start getting shorter. They are most severe during December, January and February.

In most cases, the symptoms of SAD begin to improve in the spring before disappearring.

What causes SAD?

The exact cause of SAD is not fully understood, but it is thought to be linked to reduced exposure to sunlight during the shorter days of the year.

Sunlight can affect some of the brain's chemicals and hormones. However, 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. These things can affect how you feel.

In people with SAD, a lack of sunlight and a problem with certain brain chemicals stops the hypothalamus working properly. The lack of light is thought to affect:

• the production of the hormone melatonin
• the production of the hormone serotonin
• the body's circadian rhythm (the body's internal clock that regulates a number of biological processes during a 24 hour period)

Read more about the effects of sunlight on melatonin, serotonin and the body's circadian rhythm.

Diagnosing SAD

If you have the symptoms of SAD, you should visit your GP. They may carry out an assessment to check your mental health.

You may be asked about your mood, lifestyle, eating and sleeping patterns and any seasonal changes in your thoughts and behaviour.

Read more about diagnosing seasonal affective disorder.

Treating SAD

As with any type of depression, SAD can be difficult to live with. It can make you feel tired, stressed and unhappy. However, it can usually be successfully treated.

Light therapy is often used to treat SAD. It involves sitting in front of, or beneath, a light box. Light boxes are special lamps that produce a very bright light. They come in a variety of designs, including desk lamps and wall-mounted fixtures.

Before using a light box to treat SAD, speak to your GP and check the manufacturer s instructions.

Depending on the nature and severity of your symptoms, talking therapies, such as cognitive behavioural therapy (CBT), and/or medication, such as antidepressants, may also be recommended.

Your GP will recommend the most suitable treatment programme for you which may involve using a combination of treatments.

Read more about how seasonal affective disorder is treated.