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Seasonal affective disorder (SAD)

Seasonal affective (or mood) disorder (SAD) is a type of depression with a seasonal pattern, occurring at the same time each year, most commonly in winter.

About SAD

Your sleep patterns, energy levels and mood may change in autumn and winter, and you may feel low during long periods of grey days. If this unhappiness becomes problematic every year, you may have a condition known as SAD. Mild forms of SAD are commonly called ‘winter blues.’ However, you can have a more severe form of seasonal depression that makes it hard to function in winter.

SAD is most common between the ages of 18 and 30, although it can develop at any age. It affects more women than men.

Symptoms of SAD

If you have SAD, your symptoms usually get worse in the autumn and winter, when there is less daylight. However, your symptoms can get better in spring and summer, when there is more daylight. You're more likely to have SAD if you live further away from the equator, because there are fewer daylight hours and the weather is generally cooler. You may have symptoms in the summer months at times when there is little sunshine, but this is much less common.

The symptoms of SAD can vary from person to person, and are similar to those in other types of depression. Common symptoms include:

  • low mood for most of the day
  • loss of interest in your usual activities
  • drowsiness and low energy (lethargy)
  • needing more sleep and sleeping more than usual
  • eating more than usual, especially craving carbohydrates, leading to weight gain
  • loss of interest in sex (loss of libido)
  • mood swings and excessive energy in spring and summer

Talk to your GP if you have these symptoms.

Causes of SAD

The exact cause of SAD isn't fully understood. It may be related to changes in the amount of daylight during the autumn and winter. One theory is that light stimulates a part of your brain called the hypothalamus, which controls mood, appetite and sleep. In people with SAD, lack of light and a problem with certain brain chemicals and hormones may prevent the hypothalamus from working properly. The following theories have been suggested.

  • A chemical called serotonin has a role in mood, appetite and sleep. It's thought that people with SAD may have abnormally low levels of chemicals, such as serotonin, in winter.
  • A hormone called melatonin slows down your body clock and affects sleeping and mood patterns. People with SAD may respond to a decrease in light by producing more melatonin than people without SAD. However, medicines designed to reduce melatonin don't stop the symptoms of SAD, so this isn't the only factor.

Diagnosis of SAD

Your GP is a good first point of contact. He or she will ask about your day-to-day life and symptoms. One bout of the winter blues doesn't automatically mean you have SAD. But if you have symptoms in autumn and/or winter that clear in the spring for two or more years in a row, your GP may diagnose SAD.

Your GP may also want to rule out other forms of depression.

Treatment of SAD

Treatment for SAD is similar to other forms of depression.


There are a number of steps you can take that may help reduce the effects of SAD. Wherever possible, try to:

  • find time each day to get outside
  • work in bright conditions, such as near a window
  • take regular, moderate exercise or physical activity
  • eat a well-balanced diet
  • decorate your home in light colours, which reflect the light better
  • leave any major projects until summer and plan ahead for winter
  • learn relaxation techniques and not put yourself under stress
  • take a holiday in a sunny place if you can

It’s a good idea to tell your family and friends about your condition and its effects so that they are able to help and support you. You may find it helpful to join a support group. Knowing that you are not alone and that help is available can be a great comfort.


Your GP may recommend the same antidepressant medicines that are used to treat other forms of depression.

Antidepressants work best for SAD if you start taking them before your symptoms begin and keep taking them until spring.

Talking therapies

Talking therapies are also available, which include cognitive behavioural therapy (CBT). This is a short-term psychological treatment that can help you change how you:

  • think (cognitive processes) – such as unwanted, negative thoughts and beliefs
  • feel – the emotional response you have to your thoughts
  • behave – your behaviour in response to those thoughts and feelings

Other treatments

Light therapy (also called phototherapy)

Some people find that light therapy, which is exposure to bright artificial light, improves symptoms of SAD. The idea is that providing bright light may stimulate a change in the levels of chemicals and hormones which affect your mood.

Bright light can be delivered by:

  • a specially made light box – these vary in size
  • light caps or visors that are worn on your head
  • dawn simulators – these are timed bedside lights that mimic a sunrise to wake you gradually, which can help if you find it hard to wake up in winter

The light in most light boxes is at least 10 times brighter than a normal light bulb. It's similar to natural daylight, although it won't harm your eyes or skin like strong ultraviolet (UV) light does. You should never use tanning lights or beds for light therapy. The light given out by these is high in UV rays and can harm your skin and eyes.

Most doctors advise around half an hour to an hour a day of 2,500–10,000 lux light (lux is a measure of the intensity of light). The brighter the light, the less exposure you may need. If light therapy works for you, you'll probably notice an improvement in symptoms within a week. It can, however, take up to six weeks to work.

You can use light treatment in your own home or office. If you would like to get a light box, you can buy or hire one.

Light therapy has few side-effects but some people get a headache, feel agitated and on rare occasions, feel sick.

You can ask your GP for advice before starting light therapy. You also can often hire devices rather than buy them, so try a few until you find one that you prefer.


Produced by Rebecca Canvin, Bupa Health Information Team, January 2013.

For answers to frequently asked questions on this topic, see FAQs.

For sources and links to further information, see Resources.

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  • This information was published by Bupa's Health Information Team and is based on reputable sources of medical evidence. It has been reviewed by appropriate medical or clinical professionals. Photos are only for illustrative purposes and do not reflect every presentation of a condition. The content is intended only for general information and does not replace the need for personal advice from a qualified health professional. For more details on how we produce our content and its sources, visit the about our health information page.

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