What is Seasonal Affective Disorder (SAD)?

Winter is coming.

And with it travels a dark army of long nights, conquering sunbeams on its journey across the Northern hemisphere.

Now, imagine this inevitable darkness, not only devouring the light around you, but also dimming down the sparkling electricity which normally illuminates some of the most fundamental chambers of your psyche…

Your museum of memories suddenly fails to remind you of joyful times. Your dining room no longer controls your appetite. Your activity centre no longer accommodates your zest for new experiences. And your self-esteem exhibit refuses to display any of your achievements or admirable characteristics.

For some people, seasonal changes not only happen in nature, but inside the mind as well. As days grow darker, so do thoughts. As temperature drops, so do energy levels.

The condition is known as Seasonal Affective Disorder (SAD), or, if you happen to read the Diagnostic Manual of Mental Disorders, it’s called “Major Depressive Disorder with Seasonal Pattern”.

The most common form of SAD strikes every fall or winter when there is less natural sunlight, and lifts as spring approaches. Consequently, it’s more common in people who live far from the equator. If untreated, this type of depression typically lasts for around 4-5 months, forcing you to endure several of the following symptoms:

  • low mood
  • loss of interest or pleasure in almost all activities
  • appetite and sleep disturbances
  • unusual fatigue
  • excessive feelings of guilt or shame
  • concentration difficulties
  • and suicidal thoughts or plans

Though it’s difficult to determine exactly how many people are affected by SAD, SAD-researchers1-3 suggest it’s quite common in temperate countries to experience a decrease in mood and energy during the winter months. But only around 2-5 % fall into the dusky abyss known as clinical depression.

Researchers don’t fully understand why SAD happens. A complex interaction between genetic, biochemical, environmental and cultural factors determines how each person responds to seasonal changes.

However, most researchers agree that the lack of daytime light during the winter months seems to disturb the circadian rhythm of the body, causing depression. This theory is called the phase shift hypothesis.

In a healthy person, body temperature and hormone levels rise and fall in predictable patterns over the course of a day and night. But as winter days become shorter, these natural rhythms can get out of sync with the time of day. Melatonin – a hormone which helps the body maintain the natural cycle of sleep and wakefulness – seems to play an important part.

Melatonin is produced in the pineal gland and makes us sleepy in the evening. In the morning, natural sunlight acts as a trigger for the brain to suppress melatonin and raise energy levels.

Except in people with SAD.

It is hypothesised that the winter morning light is not strong enough to suppress melatonin in people with winter depression. If affected by SAD, you spend your winter days with excess sleep hormone in your system. Awake, but not alert.

Unsurprisingly, the behavioural pattern of a person with winter onset SAD can be associated with that of a bear preparing for hibernation:

  • Hypersomnia (sleeping significantly more than usual and spending more time in bed)
  • An unusual craving for carbohydrates and overeating
  • Weight gain
  • Avoiding social contact (staying at home to “hibernate”)

And there is another type of SAD – a much less common type. It’s triggered by the arrival of spring. Spring onset SAD is associated with another behavioural pattern. As the bear wakes up from hibernation, you may experience:

  • Insomnia (significant problems falling or staying asleep and/or early morning awakenings)
  • Poor appetite and weight loss
  • Restlessness
  • Anxiety
  • Agitation
  • Violent behaviour

As with all forms of depression, it’s not enough to experience the symptoms to receive a SAD diagnosis. Other criteria apply, for example:

  • Your depressive episodes must occur during specific seasons (for example during the winter or summer months) for at least 2 consecutive years.
  • The seasonal depressive episodes must be much more frequent than other depressive episodes you may have experienced at other times of the year during your lifetime.

Evidently, SAD is different from feeling blue due to seasonal unemployment, demands connected to the big holidays or other stressors that tend to show up around the same time as the dark army invades the North.

So, how do we avoid it? How do we keep the electric circuits of our brains lit as the army of darkness overcomes our favourite ally – daylight?

Well, whether you struggle with a few symptoms or suffer from a full-blown depressive episode, there are many therapies and strategies to help you recover.

Light therapy

Winter-onset SAD is thought to occur because of a lack of sunlight. Consequently, it’s beneficial to give your light-thirsty body as much of it as possible.

People with SAD can experience significant improvements with light therapy4.

According to the phase shift hypothesis, light therapy helps restore the circadian rhythm of the body by providing it with morning light.

But to fight the dark army of winter, you need a far more powerful weapon than a regular light bulb.

The tool used in light therapy is a specially designed light box. You sit close to it for around 30-60 minutes each morning throughout the winter months.

The light box should deliver full spectrum white light at an intensity of at least 10 000 lux (about 20 times brighter than regular indoor lighting).

It’s well established that light therapy should occur in the morning and that the light must be absorbed by the eyes. Light shone on skin has no effect.

Most studies on light therapy show that a majority of people with SAD notice an improvement within 2 weeks time. For some it can be helpful within only one week, especially if used first thing in the morning.

Light therapy is considered a safe treatment. However, make sure to consult with a professional before trying it. People with an underlying bipolar disorder must be extremely cautious because intense light exposure can trigger manic episodes.

Cognitive Behavioural Therapy for SAD (CBT-SAD)

CBT is a well-known type of talk therapy aimed at restructuring the invasive negative thoughts that usually torments depressed people. In addition, CBT helps you to identify and accomplish meaningful activities and goals in your life, acting as an antidote for the loss of interest and pleasure that comes with depression.

In recent years, CBT practitioners have sharpened their weapon to make it even more impactful. There is now CBT-SAD with a special focus on negative thoughts related to the darkness, cold and other aspects of the winter season. CBT-SAD is usually structured into two weekly group sessions over the course of six weeks.

The research suggests that CBT-SAD and light therapy are equally effective at improving winter depression. Some evidence suggests that light therapy improves symptoms faster, while the positive effects of CBT-SAD seem to last longer over time.

Physical exercise

Sweating, panting and flexing your muscles is one of the safest routes to defeating depression.

As the dark army invades your mind, you can actually use your physical strength to fight off the enemy.

Along with countless other mental health researchers, Schuch and colleagues5 have concluded that physical exercise is an evidence-based depression treatment for children, adults and older adults on all continents of the world.

It’s also preventive.

In an impressive study from 2020, including 36 595 participants, Hallgren and colleagues6 found that exercising only 1-2 times a week significantly decreased the risk of depression.

Even though it seems almost cruel that when falling into a dark abyss of low mood and fatigue, you are supposed to jog and jump your way up – it is effective.

30-45 minutes of physical exercise 3-4 times a week stimulates the growth of new brain cells and protects the brain from depression and anxiety.

For more information and tips to get started: All you need to know about exercise and depression


Few people are surprised by the fact that winter depression triggers a craving for carbohydrates – it seems almost “natural” for the bear within us to gain winter weight in preparation for hibernation. However, the lesser known connection between gut bacteria and mental health still raises a few eyebrows.

In recent years, neuroscience has discovered that the battle between darkness and light is not only located inside your mind, but in your stomach as well. What you eat during winter months will inevitably impact how you think and feel.

In a research article titled “Gutted!, Thomas Bastiaansen and his colleagues explain how the brain and the gut are connected via the vagus nerve – a connection also known as the gut-brain-axis7. The stomach and the head are in constant communication with each other.

Neuroscientist Dr Uma Naidoo teaches you to feed the “good” bacteria in your gut with fibre and important vitamins, protecting your body from inflammation and thereby depression.

Another type of bacteria – the “bad” bacteria – thrive on sugar, white flour, processed meat, artificial sweeteners, stabilisers and thickeners. A high-fat, high-sugar diet causes inflammation in the body and thereby the risk of leaky gut, panic anxiety, skin rashes and depression.

So, there is reason to combat those carbohydrate cravings as well as possible. Mobilise an army of vegetables, fruit, legumes, seeds, healthy fats and whole grains to defeat some of your depressive symptoms.

For more information and recipes: Brain foods for depression

In conclusion

Even though seasonal changes can be a challenge for your mental health, you don’t stand without allies. Light therapy, CBT-SAD, exercise and nutrition are powerful enough to protect you from depression. In combination, they may even transform you into an impregnable fortress.

Hanna Silva

Clinical psychologist at Flow Neuroscience


  1. Fonte A., Coutinho B. BMC Psychiatry. 2021; 21: 317. doi: 10.1186/s12888-021-03313-z.
  2. A. Magnusson. Acta Pschiatrica Scandinavia. 2009;101, 176-184. doi: 10.1034/j.1600-0447.2000.101003176.x.
  3. Winkler D, Kasper S. Medicographia. 2005;27:247–53.
  4. NICE recommendations. https://www.nhs.uk/mental-health/conditions/seasonal-affective-disorder-sad/treatment/.
  5. Schuch, FB. PhD; Stubbs, B. PhD. Current Sports Medicine Reports. 2019; 18;8:299-304 doi: 10.1249/JSR.0000000000000620.
  6. Hallgren M, Kandola A, et al. Mental Health and Physical Activity. 2020; 19;1755-2966. doi: 10.1016/j.mhpa.2020.100351.
  7. Bastiaanssen TF. S. MSc; Cussotto S. PhD, et al. Harvard Review of Psychiatry: 1/2 2020; 28;1:26-39. doi: 10.1097/HRP.0000000000000243