But what causes it, how can it be treated and how does light help?
Here’s what you need to know.
What is SAD?
SAD is a type of depression that comes and goes in a seasonal pattern. It is sometimes known as "winter depression" because the symptoms are usually more apparent and more severe during the winter.
However, a few people with SAD may have symptoms during the summer and feel better during the winter, according to the NHS.
What are the 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
What causes SAD?
Although the exact cause of SAD is not fully understood, it’s often linked to reduced exposure to sunlight during the shorter autumn and winter days.
Priory consultant psychiatrist, Dr Natasha Bijlani, explains that “it is well recognised that SAD may be related to changes in the amount of daylight during autumn and winter months, which can affect the levels of serotonin and melatonin in the brain that influence mood.”
She says: “During the night, the brain releases melatonin which contributes to making us feel drowsy and induces sleep.
“At daybreak, the effect of bright light, coupled with the natural rhythms of the brain, suppresses melatonin.
“In those susceptible to SAD, not being exposed to sufficient light, on dull winter days, can lead to the development of the symptoms of SAD.”
The NHS also notes that 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.
What treatments are available for SAD?
A range of treatments are available for SAD. A 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 (CBT) or counselling
- antidepressant medicine – such as selective serotonin reuptake inhibitors (SSRIs)
How does light and SAD lamps help the condition?
Dr Jeff Foster explains that there is “good evidence for light therapy”, adding that light stimulation at dawn stimulation also “helps reduce symptom severity for seasonal affective disorder”.
If buying a SAD lamp, the doctor notes you should also consider the strength of the light and how long you want to be in front of it, as brighter light requires less time but can sometimes causes headaches, irritability and fatigue.
He also adds that it’s worth remembering light therapy can take several weeks to produce any effect, but if it takes longer than six weeks you should see your doctor.
“Best evidence is still that natural light is best,” Dr Foster adds.
Dr Bijlani also notes that people with SAD sometimes need four hours a day of special bright light at 10 times the intensity of ordinary lighting.
“It’s a very simple treatment, but when used regularly throughout the winter months, it can take away the worst of the feelings,” she adds.