Some people experience serious mood changes in the winter months, when there is less natural sunlight. This is called seasonal affective disorder (SAD). It is a type of depression that usually lightens as winter turns to spring and summer.

SAD occurs more frequently in women than in men and is more common where there are shorter daylight hours in winter. In most cases SAD begins in early adulthood. People with major depression, bipolar disorder (especially bipolar II), ADHD, eating disorders and panic disorders are more likely to experience SAD.

SAD is also more common in people with a family history of depression or schizophrenia.

Depression | Bipolar Disorder | Eating Disorders | Panic Disorders | Schizophrenia

SAD is generally diagnosed by means of specific questionnaires and consultations with a physician and a mental health specialist.


While the causes of SAD are not fully understood, some research indicates that people with SAD have reduced activity of a certain brain chemical which regulates moods.

Vitamin D deficiency can exacerbate these issues. The body obtains vitamin D from food but also produces it when the skin is exposed to sunlight. People who live in places where daylight is reduced in winter may have lower vitamin D levels that further disrupt brain chemical activity.

Finally, negative thoughts and emotions about winter and the associated limitations and stresses driven by cultural imperatives are common. It isn’t clear whether this negativity is a cause of SAD or an effect, but it can be a useful place to focus treatment.

Signs & Indications

SAD is a type of depression characterised by its recurrent seasonal pattern that may last four to five months each year.

SAD is like depression with some specific signs that are different for winter- and summer-pattern SAD. Not everyone shows all these signs.

  • Feeling sad, anxious or ‘empty’ for weeks or even months
  • Feeling pessimistic or hopeless
  • Feeling guilty, worthless or helpless
  • Being irritable or restless all the time
  • Losing interest in activities or hobbies
  • Feeling tired or lacking energy
  • Finding it tough to concentrate, remember details or make decisions
  • Eating or sleeping too much or too little
  • Thinking of, or attempting, suicide

Seek treatment immediately if you feel worthless or are thinking of ending your life.


There are four main categories of treatment for SAD that may be used individually or in combination:

  • Light therapy
  • Psychotherapy
  • Medication
  • Vitamin D supplements

Your healthcare provider will decide which treatment or combination is best for you.


Light therapy. People with SAD are exposed to a bright light every day for about 30 to 45 minutes. The light boxes are about twenty times brighter than indoor ambient light and filter out potentially harmful ultraviolet (UV) radiation. People with certain eye diseases or medications that increase sunlight sensitivity may not be able to undergo light therapy.

Psychotherapy. Cognitive behavioural therapy (CBT), adapted specifically for SAD, aims to reduce negative thoughts associated with the winter months, replacing them with a more positive outlook. It also helps people with SAD identify and participate in activities that combat the loss of interest they experience.


Medication. Some types of antidepressants are also used to treat SAD. A person’s physician will determine what is appropriate.


Vitamin D. People with SAD are often deficient in vitamin D. Nutritional supplements may help improve their symptoms.

Talk to your doctor or a mental health specialist if you are experiencing any signs of SAD.