Seasonal affective disorder (SAD) is a type of depression that comes and goes in a seasonal pattern.

SAD is sometimes known as "winter depression" because the symptoms are more apparent and more severe during the winter.

A few people with SAD may have symptoms during the summer and feel better during the winter.

Symptoms of SAD

Symptoms of SAD can include:

• a persistent low mood
• a loss of pleasure or interest in normal everyday activities
• irritability
• feelings of despair, guilt and worthlessness
• feeling lethargic (lacking in energy) and sleepy during the day
• sleeping for longer than normal and finding it hard to get up in the morning
• craving carbohydrates and gaining weight

For some people, these symptoms can be severe and have a significant impact on their day-to-day activities.

When to see your GP

You should consider seeing your GP if you think you might have SAD and you're struggling to cope.

Your GP can carry out an assessment to check your mental health. They may ask you about your mood, lifestyle, eating habits and sleeping patterns, plus any seasonal changes in your thoughts and behaviour.

What causes SAD?

The exact cause of SAD isn't fully understood, but it's often linked to reduced exposure to sunlight during the shorter autumn and winter days.

The main theory is that a lack of sunlight might stop a part of the brain called the hypothalamus working properly, which may affect the:

• production of melatonin – melatonin is a hormone that makes you feel sleepy; in people with SAD, the body may produce it in higher than normal levels
• production of serotonin – serotonin is a hormone that affects your mood, appetite and sleep; a lack of sunlight may lead to lower serotonin levels, which is linked to feelings of depression
• body's internal clock (circadian rhythm) –your body uses sunlight to time various important functions, such as when you wake up, so lower light levels during the winter may disrupt your body clock and lead to symptoms of SAD

It's also possible that some people are more vulnerable to SAD as a result of their genes, as some cases appear to run in families.

Treatments for SAD

A range of treatments are available for SAD. Your GP will recommend the most suitable treatment programme for you.

The main treatments are:

• lifestyle measures, including getting as much natural sunlight as possible, exercising regularly and managing your stress levels
• light therapy – where a special lamp called a light box is used to simulate exposure to sunlight
• talking therapies, such as cognitive behavioural therapy or counselling
• antidepressant medication, such as selective serotonin reuptake inhibitors (SSRIs)

A number of treatments are available for seasonal affective disorder (SAD), including cognitive behavioural therapy (CBT), antidepressants and light therapy.

Your GP will recommend the most suitable treatment option for you, based on the nature and severity of your symptoms. This may involve using a combination of treatments to get the best results.

NICE recommendations

The National Institute for Clinical Excellence (NICE) recommends that SAD should be treated in the same way as other types of depression.

This includes using talking treatments such as cognitive behavioural therapy (CBT) or medication such as antidepressants.

Light therapy is also a popular treatment for SAD, although NICE says it's not clear whether it's effective.

See the NICE guidance about the treatment and managment of depression in adults.

Things you can try yourself

There are a number of simple things you can try that may help improve your symptoms, including:

• try to get as much natural sunlight as possible – even a brief lunchtime walk can be beneficial
• make your work and home environments as light and airy as possible
• sit near windows when you're indoors
• take plenty of regular exercise, particularly outdoors and in daylight
• eat a healthy, balanced diet
• if possible, avoid stressful situations and take steps to manage stress

It can also be helpful to talk to your family and friends about SAD, so they understand how your mood changes during the winter. This can help them to support you more effectively.

Talking therapies

Talking therapies focus on both psychological aspects (how your brain functions) and social aspects (how you interact with others).

Cognitive behavioural therapy

Cognitive behavioural therapy (CBT) is based on the idea that the way we think and behave affects the way we feel. Changing the way you think about situations and what you do about them can help you feel better.

If you have CBT, you'll have a number of sessions with a specially trained therapist, usually over several weeks or months. Your programme could be:

• an individual programme of self-help
• a programme designed for you and your partner (if your depression is affecting your relationship)
• a group programme that you complete with other people in a similar situation
• a computer-based CBT programme that's tailored to your needs and supported by a trained therapist

Read more about CBT.

Counselling and psychodynamic psychotherapy

Counselling is another type of talking therapy that involves talking to a trained counsellor about your worries and problems.

During psychodynamic psychotherapy you discuss how you feel about yourself and others and talk about experiences in your past. The aim of the sessions is to find out whether anything in your past is affecting how you feel today.

It's not clear exactly how effective these two therapies are in treating depression.

Read more about psychotherapy.

Antidepressants

Antidepressants are often prescribed to treat depression and are also sometimes used to treat severe cases of SAD, although the evidence to suggest they're effective in treating SAD is limited.

Antidepressants are thought to be most effective if taken at the start of winter before symptoms appear, and continued until spring.

Selective serotonin reuptake inhibitors (SSRIs) are the preferred type of antidepressant for treating SAD. They increase the level of the hormone serotonin in your brain, which can help lift your mood.

If you're prescribed antidepressants, you should be aware that:

• it can take up to four to six weeks for the medication to take full effect
• you should take the medication as prescribed and continue taking it until advised to gradually stop by your doctor
• some antidepressants have side effects and may interact with other types of medication you're taking

Common side effects of SSRIs include feeling agitated, shaky or anxious, an upset stomach and diarrhoea or constipation. Check the information leaflet that comes with your medication for a full list of possible side effects.

Read more about antidepressants.

Light therapy

Some people with SAD find that light therapy can help improve their mood considerably. This involves sitting by a special lamp called a light box, usually for around 30 minutes to an hour each morning.

Light boxes come in a variety of designs, including desk lamps and wall-mounted fixtures. They produce a very bright light. The intensity of the light is measured in lux – the higher lux, the brighter the light.

The light produced by the light box simulates the sunlight that's missing during the darker winter months.

It's thought the light may improve SAD by encouraging your brain to reduce the production of melatonin (a hormone that makes you sleepy) and increase the production of serotonin (a hormone that affects your mood).

Sunrise alarm clocks, which gradually light up your bedroom as you wake up, may also be useful for some people.

Who can use light therapy?

Most people can use light therapy safely. The recommended light boxes have filters that remove harmful ultraviolent (UV) rays, so there's no risk of skin or eye damage for most people.

However, exposure to very bright light may not be suitable if you:

• have an eye condition or eye damage that makes your eyes particularly sensitive to light
• are taking medication that increases your sensitivity to light, such as certain antibiotics and antipsychotics, or the herbal supplement St. John's Wort

Speak to your GP if you're unsure about the suitability of a particular product.

Trying light therapy

Light boxes aren't usually available on the NHS, so you'll need to buy one yourself if you want to try light therapy.

Before using a light box, you should check the manufacturer's information and instructions regarding:

• whether the product is suitable for treating SAD
• the light intensity you should be using
• the recommended length of time you need to use the light

Make sure that you choose a light box that is medically approved for the treatment of SAD and produced by a fully certified manufacturer.

Does light therapy work?

There's mixed evidence regarding the overall effectiveness of light therapy, but some studies have concluded it is effective, particularly if used first thing in the morning.

It's thought that light therapy is best for producing short-term results. This means it may help relieve your symptoms when they occur, but you might still be affected by SAD next winter.

When light therapy has been found to help, most people noticed an improvement in their symptoms within a week or so.

Side effects of light therapy

It's rare for people using light therapy to have side effects. However, some people may experience:

• agitation or irritability
• headaches or eye strain
• sleeping problems (avoiding light therapy during the evening may help prevent this)
• tiredness
• changes to your sight, including blurred vision

These side effects are usually mild and short-lived, but you should visit your GP if you experience any particularly troublesome side effects while using light therapy.