Seasonal affective disorder (SAD) is a form of depression also known as winter depression or seasonal depression. SAD was first identified by researchers at the National Institute of Mental Health in the 1980s.1 It has been defined as a type of depression that comes and goes with the seasons. It starts and ends at about the same time every year. In the United States, the most difficult months for individuals suffering from SAD tend to be January and February. Some individuals experience SAD in the summer, even though it is much less common. Researchers have concluded that SAD stems from a problem in adapting to the physical environment. Between four and six percent of the U.S. population suffers from winter-onset SAD. Meanwhile, about 10 to 20 percent suffers from a milder form of the disorder. SAD typically begins in young adulthood, meaning that adolescents and teenagers are at risk. Some researchers have questioned whether there is actually any data in support of the existence of SAD. One study did not find a correlation between depression scores and the hours of sunlight on the day the scores were collected. Nevertheless, the findings do not negate evidence that lack of light negatively affects the mental health or the experiences of millions of individuals around the world.2
What Causes SAD?
- Low Levels of Serotonin. Serotonin is a neurotransmitter that affects mood. Reduced sunlight in the fall and winter sometimes leads to a drop in the serotonin levels, which may trigger the onset of SAD.
- Elevated Levels of Melatonin. Change in the season may disrupt the balance of melatonin, which plays a role in mood and sleep patterns. Darkness leads to increased production of melatonin in the body, which is why individuals suffering from SAD tend to feel sluggish or sleepy.
- Disturbed Circadian Rhythms. The decrease in the amount of sunlight that comes with the end of summer may disrupt the body’s circadian rhythms, or internal clock which may cause individuals to become more susceptible to SAD.
- Vitamin D Deficiency. A lack of Vitamin D has been linked to SAD. A significant amount of vitamin D comes from the sun, which means that during the darker winter months, people may suffer from a Vitamin D deficiency that results in SAD.
SAD SymptomsTo determine whether an individual is suffering from SAD, a healthcare professional usually administer a psychological as well as a physical evaluation. Lab tests may also be ordered to help determine whether a thyroid problem or a different underlying medical condition may be a contributing factor. The symptoms of SAD are similar to those of other forms of depression, including low energy, a sense of hopelessness, feelings of sadness throughout the day, difficulty concentrating, sluggishness, changes in weight or appetite, loss of interest in previously enjoyable activities, lack of self-worth and self-esteem, sleeping problems, and thoughts of suicide. Winter-onset SAD has its own specific set of additional symptoms including weight gain, craving for high-carb foods, oversleeping, heavy feeling in either the legs or arms, difficulty getting along with others, low energy, and irritability. Summer-onset SAD symptoms include episodes of violent behavior, anxiety or agitation, poor appetite, loss of weight, insomnia, and feelings of sadness.
Risk Factors for SADIndividuals with any of the characteristics provided below may be at a higher risk of suffering from seasonal affective disorder (SAD).
- Younger Age. Younger people tend to have a higher risk of developing winter-onset SAD. However, the risk of developing SAD for the first time reduces as people age.
- Being Female. About 75 percent of the people diagnosed with SAD are female. However, it also occurs in males, who are at risk of developing more severe symptoms.
- Bipolar Disorder or Clinical Depression Diagnosis. Individuals suffering from depression or bipolar disorder may experience seasonal shifts in their depression symptoms.3
- Distance from the Equator. SAD is more individuals in people living either far north or far south from the equator.