The distinguishing characteristic of seasonal affective disorder is that it’s cyclical; this type of depression occurs at about the same time every year. If you’re like most SAD sufferers, your symptoms start in the late fall and continue into winter. You may then see symptoms gradually disappear during the warmer, sunnier months of spring and summer.

Some SAD sufferers experience symptoms in the spring and summer, while others feel these symptoms in the fall and winter months. If SAD can occur at any time of year, what causes SAD?

Causes of SAD

The main cause of winter-onset SAD seems to be the reduction in sunlight that comes with shorter winter days, which may disrupt your body’s internal clock. SAD sufferers experience interferences in their natural body rhythms, from appetite to sleep cycles.

Some researchers believe that the change in season can disrupt the balance of melatonin, a hormone associated with sleep patterns and mood. Studies conducted at the Oregon Health and Science University (2007) have shown that some SAD sufferers benefit from taking melatonin supplements.

Other scientists believe that what causes SAD may be a drop in the brain’s levels of serotonin, a neurotransmitter that helps regulate mood. Reduced sunlight exposure can cause a drop in serotonin, which may lead to seasonal affective disorder.

Risk Factors for SAD

Although scientists aren’t exactly sure what causes SAD, it’s likely that age, genetics and chemical makeup all play a role in the development of the disorder.

People with certain medical conditions may be at a higher risk of developing SAD. These conditions include:

Several of these conditions interfere with the brain’s serotonin production and reception, which can cause depressive symptoms. Another risk factor for SAD is geography. Living in northern climates, where winter days are shorter and winter nights are longer, increases risk.

Gender also seems to play a role. While more women are diagnosed with seasonal affective disorder than men are, male sufferers often experience more severe symptoms.

In addition to geography and gender, age is another risk factor for SAD. Although SAD can begin at any age, onset usually occurs between the ages of 18 and 30.


American Psychiatric Association. (2010). Seasonal affective disorder. Retrieved July 10, 2010, from

Bhattacharjee, Y. (2007). Is internal timing key to mental health? Retrieved July 10, 2010, from

Lurie, S. J., Gawinski, B. Peirce

 Posted on : June 14, 2014