Seasonal affective disorder (SAD) is a type of depression that has a seasonal pattern. The symptoms often begin in the autumn as the days start getting shorter. They are most severe during December, January and February. It’s sometimes known as ‘winter depression’.
In most cases, the symptoms of SAD begin to improve in the spring before disappearing.
The symptoms of seasonal affective disorder (SAD) differ throughout the year and from person to person.
The symptoms of SAD are usually fairly mild at the start of the autumn. They might get worse as the winter progresses and the amount of sunlight decreases. However, the nature and severity of the symptoms of SAD will vary from person to person.
If you have SAD, you may experience depressive symptoms like:
You may also:
For many people, SAD can be a difficult condition to live with because it can have a significant effect on your day-to-day life.
Some people with SAD experience recurring episodes of unipolar depression. This is where you only experience depressive symptoms. Others find they experience mild episodes of bipolar depression. This is when depressed periods are followed by manic periods where you feel happy, energetic and much more sociable.
The exact cause of seasonal affective disorder (SAD) is unknown. The symptoms of depression are thought to be linked to less exposure to sunlight.
One theory is that light stimulates a part of the brain called the hypothalamus. This part controls your mood, sleep and appetite, affecting how you feel.
In people with SAD, lack of sunlight and a problem with certain chemicals in the brain prevents the hypothalamus from working properly. The lack of light is thought to affect:
your internal body clock (circadian rhythm) – your body uses sunlight to time important biological functions, like when you wake up, so lower light levels during winter may disrupt your body clock causing SAD
There are many different causes and contributing factors associated with depression. Some of these may also contribute to SAD. Possibilities include:
social factors, like your relationships with other people and whether you have close friends
SAD is often difficult to diagnose because the there are many other types of depression that have similar symptoms. It may take several years before you and your GP realise that your symptoms are forming a regular pattern.
Your GP might carry out a psychological assessment to check your mental health. During the assessment, you may be asked questions about:
Your GP may also carry out a brief physical examination to check for any other possible causes of your symptoms.
A diagnosis of SAD will depend on whether:
Your GP will recommend the most suitable treatment option for you. This may involve using a combination of treatments to get the best results.
Treatment options may include:
If other treatments like CBT, counselling and psychotherapy aren’t helping, there are some other options that might be offered to you.
Antidepressants are often only prescribed for SAD when the symptoms are severe. This is because there’s limited evidence that they’re effective.
It’s thought that they are most effective if they’re taken at the start of winter (before the symptoms appear) and continued until spring.
It can take between four and six weeks for antidepressants to take full effect. It’s also important to continue to take the medication as prescribed, even if you start to feel better.
Read more about antidepressants
Researchers think that light therapy works by simulating the sunlight that’s missing during the darker winter months.
This additional light encourages your brain to
It’s thought that altering the levels of both hormones can help to ease your symptoms of SAD.
However, there’s mixed evidence about the effectiveness of light therapy. It’s difficult to compare the research because they use a variety of light sources. Also, many of the clinical trials (medical tests) were conducted over short periods of time.
The studies which showed that light therapy is effective discovered that it’s best if used first thing in the morning.
Light therapy produces short-term results. It may help to relieve your current symptoms, but you’ll still be affected by SAD next winter.
When buying a light box, make sure that you choose one that is:
Check the manufacturer’s information and instructions to see:
The SAD Association can provide a list of recommended manufacturers.
Very bright light may not be suitable if you:
Speak to your GP if you’re unsure about a particular product or if you experience any side effects while using light therapy.
Last updated:
28 February 2024