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Understanding Seasonal Affective Disorder (SAD)

Dr Nathan Anthony specialises in the treatment of SAD, along with associated conditions such as depression and bipolar disorder, at Priory Hospital Hayes Grove and Priory Wellbeing Centre Fenchurch Street in London.

With dark nights, cold weather, the pressures of Christmas just behind us, and back-to-work fear, a lot of us can experience the ‘winter blues’; in fact it is reported that up to 28% of us can feel more depressed this time of year. But it is when these low feelings begin to have a significant negative impact on the quality of a person’s life, that it could constitute seasonal affective disorder (SAD).

SAD is a serious mental health condition which affects up to 9% of the British population. It is also reported that up to 30% of suffers may require hospitalisation for at least one period of their illness during their lifetime.

What causes SAD?


There is no doubt that an evolutionary adaptation plays a part in the existence of SAD. This is from our ancestors who lived in the northern hemisphere, who continually experienced harsh, dark winters. Unfortunately this evolutionary response does not serve a purpose in our modern lifestyles.

However, even our modern day lifestyles do not help with the existence and onset of SAD – only 10% of us now work outside in the daylight, compared to 75% of us 200 years ago.


There are of course more complex causes of SAD, with some cases being tied to strong genetic links. It is thought that SAD could form a continuum between unipolar and bipolar depression, which both have hereditary links.


It is also thought that another cause of SAD is mediated through the hypothalamus (a portion of the brain that links the nervous system to the endocrine system). The hypothalamus produces varying levels of melatonin, according to the amount of sunlight we are exposed to, which can affect our sleep and mood patterns.

The “Phase Shift Hypothesis” suggests that with less available light in the winter, we may produce an inability to synchronise circadian (body clock) rhythms with the sleep/wake cycles.

SAD is up to three times more common in women of child bearing age than men and rarely found in children or older adults.

Signs and symptoms

Recognising the difference between the ‘winter blues’ and SAD is important to ensure a patient is offered the most appropriate treatment. Signs and symptoms occur at the exact same time every year, only usually during the autumn and winter months, and 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 ideations

Symptoms of SAD share the same characteristics of depression as part of a bipolar spectrum disorder.

Patients with SAD also describe periods of marked mood elevation with increased energy in the spring. This can also be difficult to distinguish between hypomanic episodes in patients with bipolar spectrum disorders. Up to 28% of people with bipolar type 2 spectrum disorders show a seasonal variation which is similar to SAD. For this reason it can be particularly difficult to diagnose SAD.

SAD relies on a patient having symptoms at the same time of year every year, for at least two consecutive years, followed by relief of the depression usually in the spring. During this time, a GP can offer the following advice and support:

  • Keep a regular routine in terms of eating, exercise and sleeping
  • Sit near windows when indoors e.g. at work
  • Eat regular, well-balanced meals

Once diagnosed, there are certain types of treatment and therapy that can support patients with SAD. They include:

Light therapy using light boxes

Light therapy can be a very effective treatment of SAD, with most seeing an improvement of symptoms within the first week. High quality light boxes are recommended as they allow patients to spend shorter time (up to 30 minutes at a time) in the vicinity of the light box. Some patients prefer ‘lower lux’ light boxes and can have them positioned on the corner of their desks at work.

Caution should be taken when using light boxes – rapid cycling mood disorders and a switch to mania or hypomania have been known to be reported, particularly in patients with a bipolar spectrum disorder, with a seasonal component.

Guidance for buying light boxes can be found on the SADA website here:

Talking therapies

There is increasing evidence that cognitive behavioural therapy (CBT) may be helpful in alleviating winter depressions and possibly preventing it from re-emerging in the future.

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

It also attempts to help patients understand and adjust underlying belief patterns which maintain these dysfunctional thinking patterns and behaviours. Teaching people to challenge cognitions and modify their behaviour can lead to a significant improvement in mood.


Selective serotonin reuptake inhibitors (SSRIs) are the most effective form of treatment particularly when used alongside therapy. To be most effective, fluoxetine or sertraline should be started in the autumn and discontinued in the spring. Caution must be taken for patients who may have an underlying bipolar spectrum disorder.

Priory offers tailored treatment programmes for individuals suffering with SAD. Our nationwide network of hospitals and wellbeing centres provides the choice of inpatient, outpatient or day patient care for this condition.

Get in Touch Today

For details of how Priory can provide you with assistance regarding mental health and wellbeing, please call 0800 840 3219 or click here to submit an enquiry form. For professionals looking to make a referral, please click here

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