Seasonal affective disorder (SAD)

Seasonal affective disorder (SAD) is a type of depression that typically affects people during the dark winter months. If the dark mornings and early sunsets affect your mood significantly, read on to learn more about SAD and how it can be managed.

What is seasonal affective disorder?

Seasonal affective disorder (SAD) is a recurring type of major depressive disorder (MDD) which occurs every winter. Although the cause for SAD is still uncertain, it occurs during the times of the year when periods of daylight are shortest. SAD symptoms typically reduce in the spring, and dissipate through the summer, until the following winter.

Reduced sunlight in the winter can disrupt the body’s biological clock and reduce the levels of important hormones in the brain:

  • Serotonin which stabilises mood and feelings of wellbeing as well as helping with sleeping, eating, and digestion
  • Melatonin which regulates sleep and influences the control of mood and behaviour

The prevalence of SAD is 1.5% to 9% of the population depending on the country’s latitude. In Nordic countries, where light is restricted during winter months, rates of SAD are around 15%. Studies of twins and families with SAD suggest there is also a genetic component. Relatives of SAD patients have higher rates of SAD (14% to 26%).

What are the symptoms of SAD?

Symptoms of SAD have a negative effect on patients’ lives. Feeling sad, lonely, or depressed at times is a normal reaction to life events such as the loss of a loved one or stress at work. However, if these feelings are intense and last for a long time, you may have depression. If these feelings are seasonal, you may have SAD.

The symptoms of SAD are like those of MDD:

  • Lack of energy and fatigue
  • Feelings of sadness or anxiety
  • Irritability or restlessness
  • Feelings of guilt or worthlessness/helplessness
  • Feeling less social than usual
  • Difficulty sleeping
  • Trouble concentrating, remembering details, and making decisions
  • Craving carbohydrates

SAD usually starts in adults aged 18 to 30 years. It is four times more common in women than men, unlike MDD which is only twice as common in women.

Symptoms which are more common in SAD than MDD are fatigue, increased sleep, appetite and weight gain. Patients also yearn for carbohydrates and prefer eating at night, both of which can lead to increased weight.

How is SAD diagnosed?

The criteria for diagnosing MDD is having five or more of the following symptoms. They must occur most of the day, nearly every day, and during a same two-week period. Additionally, one of these symptoms must be one of the first two listed:

  1. Depressed mood
  2. Loss of interest or pleasure, in all, or almost all, activities
  3. Non-intentional weight loss or decrease/increase in appetite
  4. Slowing down of thought processes and physical movement (as observed by others)
  5. Fatigue or loss of energy
  6. Feelings of worthlessness or excessive or inappropriate guilt
  7. Reduced ability to think or concentrate, or indecisiveness
  8. Recurrent thoughts of death or suicide

SAD is also known as MDD with seasonal pattern. Therefore, the additional criteria for diagnosing MDD with seasonal pattern is:

  • Symptoms reoccurring at specific times for at least two consecutive years, with no non-seasonal episodes of MDD
  • A time correlation between the onset/remission of symptoms and the time of year
  • Occurrence of more seasonal, than non-seasonal, episodes during the patient’s life

As with any other types of MDD, it is important to exclude conditions which may mimic the symptoms of depression. These can include:

  • Substance abuse
  • Medical conditions including hypothyroidism (underactive thyroid gland)
  • Infectious mononucleosis (glandular fever)

What are the treatments for SAD?

SAD can be treated with a number of treatments including:

  • Antidepressants
  • Light therapy
  • Cognitive behavioural therapy (CBT)
  • A combination of the above treatments


Antidepressants are effective in people with SAD, especially for those with intense symptoms. Since low serotonin links to SAD, antidepressants known as selective serotonin reuptake inhibitors can be effective. One example is fluoxetine (Prozac) which increases the levels of serotonin.

Light treatment and dawn simulation

Light treatment involves daily exposure to bright white full‑spectrum fluorescent light. It is sometimes also called bright light therapy. This lasts from 15 minutes to three hours a day. Dawn simulation consists of exposing sleepers to a gradually increasing intensity of light. This lasts for 30 minutes or more before waking. Both light treatment and dawn simulation are effective for the treatment of SAD. It is said to have results similar to antidepressants. The efficacy of these light-related treatments reinforces the concept that SAD is related to sensitivity to light.

Light treatment

Light treatment produces a similar effect to natural light, by generating the chemicals in the brain that help regulate mood. Between 60% and 80% of patients with SAD are known to benefit from light treatment. Daily administration of light therapy is now recognised as a first-line treatment for SAD. When administered in combination with an antidepressant, it has an additive effect to that of the antidepressant.

Dawn simulation

Dawn simulation can be effective, particularly for patients who do not have the time for light therapy, or those with sleep problems. Dawn simulation involves a gradual increase of light output, peaking at 250 lux, applied from 4:30am to 6:00am. It achieves superior results to light therapy administered for 30 minutes in the early morning.


Short courses of psychotherapy, such as CBT or individual psychotherapy sessions, achieve similar results to light therapy. It is effective for most symptoms of SAD, except for insomnia. A CBT course that has been especially adapted for SAD patients (CBT-SAD) is particularly effective. It consists of two sessions of group therapy per week for six weeks. It looks at patients’ perceptions and reasoning and develops coping strategies for the winter season.


Evidence shows vitamin D deficiency is associated with depression. The development of MDD is associated with deficiency of other nutrients such as:

  • B vitamins
  • Omega-3
  • Polyunsaturated fatty acids
  • Zinc
  • Antioxidants

Poor memory, lack of concentration and difficulties with decision making can also be experienced. This suggests a role for vitamin D and mineral supplements in reducing depression symptoms.

A typical Nordic diet contains lots of oily fish which is rich in omegas and vitamin D. This means it provides inhabitants with a natural defence against depression.

Preventative treatment

Given SAD is predictable, occurring at the same time each winter, preventative treatment should be possible. SAD patients should spend as much time as possible outside to benefit from the effects of daylight. They should also receive light therapy before the usual time of onset of their SAD. Additionally, cod liver oil tablets and vitamin D supplements can help minimise the onset of SAD.

Need some support?

If you are struggling with feelings of depression, anxiety or anger, our Leukaemia Counselling Service provides those affected by leukaemia, MDS or an MPN diagnosis. Find out more here.

Donate to Leukaemia Care today

Your donation will help to fund our vital support services that work tirelessly to ensure that people affected with leukaemia get the financial, emotional, and informational support they need.

Read More