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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.

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.

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  • Symptoms 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.

    Bupa Health Assessment: Mental health check

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  • Diagnosis 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 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.

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  • Causes 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.
  • FAQs FAQs

    Could my diet help my seasonal affective disorder (SAD)?


    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 brain’s ability to produce certain chemicals, and so 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), eggs and bananas.
    • 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. Eating enough of these may help to prevent depression and keep your mood stable. The best source of omega-3 is oily fish, such as fresh tuna, salmon and mackerel.
    • Folic acid. There is some evidence that having enough of the vitamin folic acid in your diet may help to stabilise your mood. Good sources of folic acid include leafy green vegetables, some fruit, and bread and cereals fortified with folic acid.
    • Selenium. This has been linked to helping make your mood more stable, and is found in cereals, meat, fish and eggs.

    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 – less than a metre away. To get any beneficial effects, you must make sure that the light can shine into 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.

    What is the best type of light therapy?


    Different devices may suit different people so you could try a few to find out which is best for you.


    The type of device that you choose is down to your 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, you could 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 travel a lot or want to move about and do things during light therapy.

    Different devices also have different powers or intensity of light. Those with a lower power or intensity aren't any 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.

  • Resources Resources

    Further information

    Mental Health Foundation The Mental Health Foundation is a charity that carries out research and offers information about many areas of mental health. This page complements our content about SAD with additional detail about its symptoms and the ways the condition can affect you.


    • Depression – Background information. NICE Clinical Knowledge Summaries., published February 2010
    • Understanding seasonal affective disorder. Mind., published 2011
    • Seasonal affective disorder. Royal College of Psychiatrists., published May 2010
    • Seasonal affective disorder. Mental Health Foundation. accessed 13 July 2012
    • Taylor-Walker C. The basics – seasonal affective disorder. GP Online CPD article., published January 2011
    • Treatment. SAD Association., accessed 20 July 2012
    • Nutrition. Royal College of Psychiatrists., published August 2009
    • Feeding minds: The impact of food on mental health. Mental Health Foundation., accessed 20 July2012
    • The links between diet and behaviour: The influence of nutrition on mental health. Report of an enquiry held by the associate parliamentary food and health forum., published January 2008
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