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 usually 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.
The exact causes of SAD aren't clear. It seems that the things we know can cause depression in general can lead to SAD, and research has also suggested that there are a few things that could contribute to the development of SAD in particular.
Depression can vary a lot between different people and you might have SAD due to a combination of factors, or there might not seem to be any specific reason.
When light hits the back of your eye, messages go to the part of your brain that controls sleep, appetite, sex drive, temperature, mood and activity. If there isn't enough light, these functions can slow down and gradually stop.
Some people seem to need a lot more light than others. This may mean they're more likely to get SAD during winter months. Some people seem to have the opposite experience, finding bright light and sunshine hard to cope with.
Your brain sets your body clock by the hours of daylight. One theory is that if you experience SAD, this part of your brain isn't working in the same way. This could mean your body clock slows down, leading to tiredness and depression.
Some researchers think this is because your sleep pattern (also known as your 'sleep phase') starts at a different time. This is sometimes described as having a delayed sleep phase.
SAD is thought to be more common in countries where there are greater changes in the weather and daylight hours during different seasons, including England and Wales. People who live near the equator for part of their lives and then move further away may also be especially vulnerable to getting SAD.
When it's dark, your brain produces a hormone called melatonin which helps your body get ready for sleep. Some people with SAD seem to produce much higher levels of melatonin during winter (which is also what happens to animals when they hibernate).
The exact relationship between melatonin and SAD isn't clear. Researchers have found that if you have high levels of melatonin and you're exposed to bright light, your melatonin levels drop to a more usual amount. But this doesn't seem to help with symptoms of depression.
We all have different experiences of particular seasons and types of weather. You might feel particularly uncomfortable in hotter or colder temperatures, which could contribute to you developing depression (or any existing depression worsening) at those times.
While more people are aware of SAD happening in winter, some people have more difficulty in warmer weather. Some studies have suggested a possible link between higher temperatures and poor mental health, but more research is needed to understand why.
Whether or not you have symptoms of SAD, there might be some occasions or times of year you find especially difficult – for example, due to upsetting memories of abuse, bereavement, money problems, housing problems, loneliness or other mental health problems that get worse at particular times of year. Occasions like Christmas can also be particularly stressful, whether or not you have SAD in winter.
Looking after your physical health can make a difference to how you feel emotionally. For example, it can help to:
If you've noticed your symptoms follow a pattern, you may be able to work out when they're most likely to start in the future. This may help you put things in place for those times.
For example you could:
Some people find it helpful to fill a box with things that comfort them or help them to relax. You could try including your favourite book or film, a notebook and pen to write down your thoughts or notes of encouragement to yourself. This can be a useful tool as it can be very difficult to come up with ideas to help you when you're feeling low.
You might find it helps to keep a note of your symptoms, including when they start and if particular things seem to trigger them, including changes in the weather. This could help you notice any patterns.
You could also make a note of things that feel helpful for you or which seem to make things worse. This can be helpful because SAD affects you at some times and not others, so you might not easily remember these details.
If SAD affects you during hot weather, there are particular things you could try that might help. You could:
If SAD affects you during winter, there are particular things you could try that might help. You could:
A number of treatments are available for seasonal affective disorder (SAD), including cognitive behavioural therapy, 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.
Things you can try yourself
There are a number of simple things you can try that may help improve your symptoms, including:
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.
Psychosocial treatments 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:
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 2 therapies are in treating depression.
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:
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.
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.
Dawn-stimulating alarm clocks, which gradually light up your bedroom as you wake up, may also be useful for some people.
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).
Who can use light therapy?
Most people can use light therapy safely. The recommended light boxes have filters that remove harmful ultraviolet (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:
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:
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:
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.