The specific cause of seasonal affective disorder remains unknown, but the lack of sunlight is considered as one of the main contributing factors.

Imbalances that Result from an Inadequate Amount of Light

Because of the reduced sunlight in the fall and winter months, the winter blues can appear as early as November. The lack of sunlight can affect body functioning in any of the following ways:

  • One’s biological clock, otherwise known as the circadian rhythm, can be thrown off-balance because of insufficient light. Because sufferers often awake when it is still dark and go home when the sun is setting, their internal clock may not be able to distinguish the times when they should be awake or when they should sleep. As a result, people suffering from seasonal affective disorder may find that they tend to nap during the day or have trouble sleeping at night. Or, they may tend to oversleep. Either way, the imbalance can lead to depression.
  • The regulation of the hormone melatonin can also be disrupted as well. A lack of light can cause an overproduction of the substance, all which can lead to depressive episodes.
  • In addition, serotonin, a chemical or neurotransmitter in the brain, can also be affected by a lack of UV light. Sunlight increases the level of serotonin in the body which also improves one’s mood.
  • Exposure to the sun is necessary as well to increase the level of vitamin D, a nutrient that is found to be deficient in most people who suffer from the winter blues.

Factors increasing the risk of Seasonal Affective Disorder


Seasonal affective disorder is diagnosed far more often in women than in men, but men may have more severe symptoms. It is of course possible that men don’t report symptoms as frequently as women. On the other hand the differences in body chemistry and hormones between men and women may make women more prone to developing winter blues.

Geographical location

Seasonal affective disorder appears to be more common among people who live far north or south of the equator. As decreased sunlight is thought to be the main cause of SAD it is likely that people living closer to the poles are also at a higher risk for more severe symptoms occurring.during the winter.

Family history

As with other types of depression, if you have blood relatives with the condition it is more likely that you will also develop seasonal affective disorder.

Other type of depression

Symptoms of depression may worsen seasonally if you have clinical depression, bipolar disorder or a similar condition.


Seasonal Affective Disorder is more likely to occur between the ages of 15 and 55. The initial onset of  the depression is highest in those between the ages of 18 and 30.

Other factors

The occurrence of symptoms is influenced by a number of other factors as well. Your general physical and mental health, as well as stress level, diet and sleep can all play a part.