What is Seasonal Affective Disorder?

What is Seasonal Affective Disorder?

Seasonal Affective Disorder (SAD) affects an estimated 10 million people in the United States, with up to 20 million more experiencing some depressive symptoms. It presents as similar to depression except it strikes only at certain times of the year, most often during the winter months. It can also occur during the summer but it is much less common. SAD has often been referred to as the “winter blues” but that name better represents a non-clinical form of SAD. While many people feel a bit down during the winter, the symptoms of SAD are more severe.


People with SAD have many of the same symptoms of major depression. More specific symptoms of winter-onset SAD include:

  • Oversleeping
  • Increased appetite
  • Weight gain
  • Tiredness or low energy
  • Isolation

Symptoms specific to summer-onset SAD include:

  • Insomnia
  • Weight loss
  • Agitation or anxiety


The exact cause of SAD is unknown. However, its occurrence has been linked to the following factors:


People with SAD appear to have less serotonin activity during the winter months. Low serotonin levels are associated with depressive symptoms.


Melatonin is the hormone that helps the body fall asleep. People with SAD appear to overproduce melatonin during the winter and, as a result, are more tired and lethargic. Although humans are not bears, you can understand why there is a tendency to hibernate during the colder months. 

Circadian Rhythms

People with SAD have more difficulty adjusting to the shift in body rhythms brought on by increasing darkness. Disruption in the body clock leads to feelings of depression

Vitamin D

People with SAD produce less vitamin D. Deficiency in vitamin D has been linked with less serotonin production and depressive symptoms.


Some of the treatments for SAD are similar to those for depression but also contain some specific interventions related to winter conditions.

Light Therapy

One of the main problems with winter is the lack of light. Light has a tremendous impact on shifting our circadian rhythms. It also stops melatonin from being produced and increases vitamin D intake. People who suffer from SAD appear particularly susceptible to the negative effects of increased darkness. Sitting in front of lightboxes that mimic full-spectrum sunlight is effective in reducing SAD symptoms. A person will need to dedicate up to an hour a day to exposure to full-spectrum light. Besides lightboxes, you can also purchase full spectrum lightbulbs. In addition, it is recommended to spend as much time as possible outside during the winter months.

Vitamin D Supplementation

Taking supplements for vitamin D has shown some promise in helping reduce the occurrence of SAD. It is recommended to take 100,000 IU daily as well as increasing the intake of foods rich in Vitamin D (e.g., salmon, mushrooms, milk).

Antidepressant Medication

Antidepressant medication is effective in treating major depression and SAD. Because of SAD’s association with decreased serotonin levels, it makes sense that medication that increases serotonin (e.g., SSRIs) would reduce symptoms.


Talk therapy, especially cognitive behavioral therapy (CBT), is effective in reducing SAD. CBT aims to change negative thinking patterns and behavior that contributes to depressive symptoms.

SAD can cause considerable misery during the winter months. Cold weather and reduced sunlight contribute to physiological and psychological issues that are particularly sensitive to people with SAD. Luckily, there are treatment options that reduce negative symptoms and can help make winter a season to be enjoyed.


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