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Page medically reviewed by Dr Rupesh Adimulam (MBBS, MRCPsych), Consultant Neuropsychiatrist at Priory Hospial Chelmsford in January 2022.

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Definition  |   Warning signs and symptoms  |   Causes and Risk Factors  |   Treatment

What is seasonal affective disorder (SAD)?

Seasonal affective disorder (SAD), sometimes known as ‘winter depression’, is a type of depression and formally recognised mental health condition. The symptoms of SAD, including persistent low moods, a lack of energy, and poor concentration, are typically experienced in a seasonal pattern, emerging in the winter months when people are exposed to less natural daylight, and decreasing in spring and summer.

The majority of people with SAD live in the northern and southern hemispheres (places that experience longer hours of darkness during winter). SAD is much less common in those living near the equator, where daylight hours are reliably long and bright.

What are the warning signs of seasonal affective disorder?

seasonal affective disorder symptoms and causes

The signs and symptoms of SAD will typically occur at a similar time every year, usually during the autumn and winter months when there's less sunlight. They include:

  • Feeling low and depressed
  • Feeling excessively tired during the day and needing to sleep for longer
  • Having difficulty getting up in the morning despite having more sleep
  • Social withdrawal and loss of pleasure and interests
  • Loss of libido
  • Feelings of irritability, tension, stress and anxiety
  • Carbohydrate cravings, waking up in the night to eat, and weight gain
  • Feelings of despair, guilt and worthlessness
  • Suicidal thoughts

If the signs you're experiencing align with that of seasonal depression, you can make one or two changes to your daily routine that will help you cope with seasonal affective disorder

Why does the weather affect my mood?

The exact cause of SAD can differ depending on each individual, just as the causes of all types of depression do. It may also be a combination of things that contribute to the likelihood of you developing SAD. However, there are a few distinct factors that research shows are linked to SAD.

Poor sleep patterns

Your body’s internal clock, known as your circadian rhythm, uses sunlight as a guide for o when you should wake up or go to sleep. With the lower levels of sunlight during winter, your body’s biological clock may become disrupted, leading to symptoms of SAD.

Serotonin and Melatonin levels

It is also believed that SAD may be related to the activity of the hypothalamus (a portion of the brain that links the nervous system to the endocrine system). The hypothalamus produces varying levels of melatonin (the ‘sleep hormone’), according to the amount of sunlight we are exposed to, which can affect our sleep and mood patterns.

Similarly, less sunlight can lead to a drop in how much serotonin we produce. Serotonin is a brain chemical that affects our mood, so any reduction can lead to symptoms of depression.

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Why do people get seasonal affective disorder?

There are some additional factors that might make someone more vulnerable to developing SAD. These include:

  • Age: The risk of being affected by SAD decreases with age, with the highest rate of cases among those aged 18-30
  • Gender: Women are more likely to experience SAD than men
  • Location: Rates of SAD are higher in parts of the world with less sunlight and longer winter nights. In general, the further you go from the equator the more at risk you are of SAD. If you work outside, allowing you to get more sunlight, this might also decrease your risk of developing SAD
  • Family history: Genetics can play a role in causing SAD. If you have a family history of SAD, or other types of depression, then you may be at higher risk of developing the condition yourself

If you already suffer from depression, SAD can increase the existing depression symptoms that you experience throughout the rest of the year. If you find there’s a link between you feeling depressed and the nights drawing in during winter, it’s important to understand that SAD is a treatable condition. It’s crucial that you seek help as early as possible, so that you can start your journey towards recovery.

Seasonal affective disorder treatment

To be diagnosed with SAD, your symptoms of depression would resurface on an annual basis, coinciding with the winter months and lessen when spring returns. For those who are suffering with SAD, know that there are treatment options available that can help you to reduce symptoms and continue to live your life the way you want to, no matter the time of year.

Common SAD treatments include:  

Light therapy using lightboxes

Light therapy can be a very effective treatment for SAD, with most seeing an improvement of symptoms within the first week. A powerful lamp that replicates natural light, high-quality lightboxes are recommended as they allow patients to spend a shorter time (up to 30 minutes at a time) using them. Some patients prefer ‘lower lux’ lightboxes, as these can be positioned on the corner of their desks at work. The sunlight that light therapy imitates helps trigger the releases of serotonin in the brain, helping to improve your mood.

Some people also find dawn simulators to be an effective treatment of SAD. Essentially a light-based alarm clock, a dawn simulator has a timer that you adjust before you go to sleep. The light in a dawn simulator mimics the morning sunrise, aiding your body clock and ensuring a healthier sleep pattern. 

Guidance for buying lightboxes, including any risks involved, can be found on the SADA website.

Talking therapies

Cognitive behavioural therapy (CBT) is also known to be helpful in alleviating winter depression and possibly preventing it from re-emerging in the future.

CBT identifies the link between our thoughts, behaviour and mood. Therapy involves helping people to become more aware of their negative thought patterns, which can lead to unhealthy behaviours and emotions.

It also helps people to adjust any underlying beliefs they may have, which could be maintaining their unhealthy thinking patterns and behaviours. Teaching people to challenge their negative thoughts and modify their behaviour, can lead to a significant improvement in mood.


Selective serotonin reuptake inhibitors (SSRIs), a type of antidepressant, is an effective treatment particularly when they are taken alongside therapy. To be most effective in treating SAD, SSRIs such as fluoxetine or sertraline, should be started in the autumn and discontinued in the spring.  Antidepressants can be prescribed by your GP or a psychiatrist – make sure you speak to your doctor or read the leaflet to understand any side effects or risks associated with them.

Getting Help for Seasonal Affective Disorder

At Priory, our treatment specialists are committed to ensuring that we provide a high-quality depression treatment programmes that’s structured within the National Institute for Health and Care Excellence (NICE) guidelines.  

SAD treatment can be delivered on an outpatient basis at Priory, which consists of you attending one of our Priory hospitals or wellbeing centres for a series of flexible therapy sessions. It might also be appropriate for you to undergo an inpatient treatment programme, where you stay at one of our UK hospitals on a residential basis and receive round-the-clock support for your SAD. You can read more about Priory’s inpatient and outpatient offerings on our approach to treatment page.

Make an enquiry today and get the help that you need to get your life back on track. Our highly qualified mental health professionals are ready to talk through your situation and help you to begin your recovery journey.  

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For details of how Priory can provide you with assistance regarding mental health and wellbeing, please call 0330 056 6020 or click here to submit an enquiry form. For professionals looking to make a referral, please click here

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