Seasonal affective disorder

This factsheet is for people who have seasonal affective (or mood) disorder (SAD), or who would like information about it.

SAD is a type of depression with a seasonal pattern, occurring most commonly in the winter months.

Click on the tabs below for more information about SAD.

Published by Bupa's Health Information Team, April 2011.

About SAD

About SAD

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 referred to as winter blues but you can have a more severe form where you’re unable to function in winter.

You're more likely to have SAD the further you live from the equator where the number of daylight hours is reduced and the weather is generally cooler. More people have SAD in northern Europe, Canada and Scandinavia. You may find you have symptoms in the summer months at times when there is little sunshine, but this is much less common.

SAD is most common between the ages of 18 and 30, although it can develop at any age. More women are affected than men.

Causes of SAD

The exact cause of SAD isn't fully understood.

SAD may be related to changes in the amount of daylight during the autumn and winter. One theory is that light stimulates a part of the 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 the body clock, and affects sleeping and mood patterns. People with SAD may respond to a decrease in light by secreting more melatonin than people without SAD. However, medicines designed to suppress the secretion of melatonin don't stop the symptoms of SAD, so this isn't the only factor.

Symptoms and diagnosis

Symptoms and diagnosis

Symptoms of SAD

If you have SAD, your symptoms usually get worse in the autumn and winter when the days are shorter, but your symptoms go in spring and summer when the days are longer.

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

  • low mood for most of the day
  • loss of interest in your usual activities
  • drowsiness and indifference (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
See a doctor if you have these symptoms during the winter months.

Diagnosis of SAD

If you see a doctor with symptoms of SAD, 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 for two or more consecutive years in autumn and/or winter which clear in the spring, the diagnosis may be SAD.

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



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, you should:

try to find time each day to get outside
sit near windows when you are inside
take regular, moderate exercise or physical activity
eat a well-balanced diet
decorate your home in light colours
leave any major projects until summer and plan ahead for winter
not put yourself under stress and learn relaxation techniques
Tell your family and friends about the 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 doctor may recommend antidepressant medication normally used for other forms of depression.

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

Talking therapies

Your doctor may also recommend talking therapies, such as cognitive behavioural therapy (CBT). CBT is a short-term psychological treatment that helps to change the way you think, feel and behave. CBT is a combination of two types of therapy:

  • cognitive therapy, which helps with thinking processes such as unwanted thoughts, attitudes and beliefs (called cognitive processes)
  • behavioural therapy, which focuses on behaviour in response to those thoughts

Other treatments

Light therapy (also called phototherapy)

Some people find light therapy (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 range in size
  • light caps or visors that are worn on the head like a baseball hat
  • dawn simulators - these are timed bedside lights that mimic a sunrise and wake you gradually (these help only some of the symptoms of SAD)
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.

There is no recommended amount of light as there is limited evidence that this treatment works. On average, most people use one hour of 5,000 lux of light per day (lux is a measure of the intensity of light). This can also be given as 2,500 lux for two hours or 10,000 lux for 30 minutes each morning during the autumn and winter months. You may notice an improvement in symptoms within three to five days but it may take a week or more to see any effects.

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.

Ask your doctor for advice before starting light therapy.

Availability and use of different treatments may vary from country to country. Ask your doctor for advice on your treatment options.



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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 peer reviewed by Bupa doctors. This content was compiled by Bupa based on clinical information and practice current as at the stated date of publication. Content is likely to reflect clinical practice in a particular geographical region (as indicated by the sources cited) – accordingly, it may not reflect clinical practice in the reader’s country of habitation. This content is intended for general information only and does not replace the need for personal advice from a qualified health professional. Photos and videos are only for illustrative purposes and do not reflect every presentation of a condition.

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