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

About SAD
Symptoms of SAD
Causes of SAD
Diagnosis of SAD
Treatment of 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.

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


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. 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. You may find you 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 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

You can see your GP if you have these symptoms during the winter months.


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.


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 for two or more consecutive years in autumn and/or winter which clear in the spring, the diagnosis may be 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, 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 GP 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

Talking therapies are also available, which include 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.

You can ask your GP for advice before starting light therapy.

Answers to questions about seasonal affective disorder

This section contains answers to common questions about this topic. Questions have been suggested by health professionals, website feedback and requests via email.

Could my diet help my seasonal affective disorder?
Which type of light therapy is most effective?
Do I need to look directly at the light when I use a light box?

Could my diet help my seasonal affective disorder?

Various nutrients have been linked to mood, including complex carbohydrates, tryptophan, omega-3 fatty acids and folic acid. Eat a varied and balanced diet to make sure you are getting all the nutrients you need.


It's important to maintain a healthy, balanced diet if you have seasonal affective disorder (SAD), as the food you eat may affect your mood. Some nutrients are thought to be linked with depression.

  • Tryptophan – this is an amino acid that your body needs to produce serotonin, a chemical involved with mood, sleep and appetite. Sources of tryptophan include lean meat (especially poultry), and eggs.
  • Complex carbohydrates – foods high in complex carbohydrates can help to increase the levels of tryptophan in your brain. Sources include brown rice and pasta, wholegrain bread, beans and broccoli. It's common to want to eat more carbohydrates than usual if you have SAD, so try to opt for wholegrain types, and remember to balance this with plenty of fruit and vegetables.
  • Omega-3 fatty acids may also help to reduce symptoms of depression The best source of omega-3 is oily fish, such as fresh tuna, salmon and mackerel.

Folic acid – there is some evidence that the vitamin folic acid may help to improve mood. Good sources of folic acid include leafy green vegetables, some fruit, and bread and cereals fortified with folic acid.

Which type of light therapy is most effective?

Exactly how well light therapy works isn’t clear. Different devices may suit different people. You could try a few to find out which is best for you.


The type of device that you may choose is down to your particular needs and circumstances.

  • If you plan to use your device at home and usually have an hour or so where you can sit down to read a book, watch television or eat a meal, you may find that a light box is best.
  • If you want to use a device at work, try a desk lamp or light box that can be fitted to your computer monitor.
  • Devices that are used as a bedside lamp to simulate sunrise may help if you work irregular hours or if you find it most effective to receive light first thing in the morning, for example, if you dread getting up on dark mornings.
  • A visor may be best if you're always on the go or travel a lot.

Different devices also have different powers or intensity of light. Those with a lower power or intensity aren't any more or less effective; you just need to use them for longer to get the same effect. They are generally cheaper than higher power devices. You may decide that it's worth paying more to get a therapy that may work faster; or if you have time to spare, you may decide to save money and buy a lower power light.

You can often hire devices rather than buy them, so try a few until you find one that you prefer.


Do I need to look directly at the light when I use a light box?

No. The light box needs to be in your field of vision, so that the light can reach your eyes. However, you don’t need to stare at the light directly.


You should sit close to the light box – about an arm's distance away. To get any beneficial effects, you must make sure that the light can enter your eyes. You need to be awake and shouldn't wear sunglasses or anything else covering your eyes.

You can do other activities while you're using light therapy, such as eating, watching TV, reading or working at a computer; but keep your body faced towards the light, so that it's always in your field of vision.

Further information

SAD Association

0845 766 0163

Mental Health Foundation


  • Depresión Clinical Knowledge Summaries., published February 2010
  • Understanding seasonal affective disorder. Mind., accessed 23 March 2010
  • Seasonal Affective Disorder (SAD). Mental Health Foundation., published 2000
  • Depression: the treatment and management of depression in adults: updated edition. National Collaborating Centre for Mental Health and National Institute for Health and Clinical Excellence (NICE), 2009.
  • Seasonal affective disorder. Clinical Knowledge Summaries., accessed 24 March 2010
  • Seasonal Affective Disorder – Information, Advice and Answers. SAD Association., accessed 24 March 2010

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