What is seasonal affective disorder?
Many people go through short periods of time where they feel sad or not like their usual selves. Sometimes, these mood changes begin and end when the seasons change. People may start to feel “down” when the days get shorter in the fall and winter (also called “winter blues”) and begin to feel better in the spring, with longer daylight hours.
In some cases, these mood changes are more serious and can affect how a person feels, thinks, and handles daily activities. If you have noticed significant changes in your mood and behavior whenever the seasons change, you may be suffering from seasonal affective disorder (SAD), a type of depression.
In most cases, SAD symptoms start in the late fall or early winter and go away during the spring and summer; this is known as winter-pattern SAD or winter depression. Some people may experience depressive episodes during the spring and summer months; this is called summer-pattern SAD or summer depression and is less common.
What are the signs and symptoms of SAD?
SAD is not considered a separate disorder but is a type of depression characterized by its recurrent seasonal pattern, with symptoms lasting about 4 to 5 months per year. Therefore, the signs and symptoms of SAD include those associated with major depression, and some specific symptoms that differ for winter-pattern and summer-pattern SAD. Not every person with SAD will experience all of the symptoms listed below.
Symptoms of major depression may include:
- Feeling depressed most of the day, nearly every day
- Losing interest in activities you once enjoyed
- Experiencing changes in appetite or weight
- Having problems with sleep
- Feeling sluggish or agitated
- Having low energy
- Feeling hopeless or worthless
- Having difficulty concentrating
- Having frequent thoughts of death or suicide
- Oversleeping (hypersomnia)
- Overeating, particularly with a craving for carbohydrates
- Weight gain
- Social withdrawal (feeling like “hibernating”)
What causes SAD?
Scientists do not fully understand what causes SAD. Research indicates that people with SAD may have reduced activity of the brain chemical (neurotransmitter) serotonin, which helps regulate mood. Research also suggests that sunlight controls the levels of molecules that help maintain normal serotonin levels, but in people with SAD, this regulation does not function properly, resulting in decreased serotonin levels in the winter.
Other findings suggest that people with SAD produce too much melatonin—a hormone that is central for maintaining the normal sleep-wake cycle. Overproduction of melatonin can increase sleepiness.
Both serotonin and melatonin help maintain the body’s daily rhythm that is tied to the seasonal night-day cycle. In people with SAD, the changes in serotonin and melatonin levels disrupt the normal daily rhythms. As a result, they can no longer adjust to the seasonal changes in day length, leading to sleep, mood, and behavior changes.
Deficits in vitamin D may exacerbate these problems because vitamin D is believed to promote serotonin activity. In addition to vitamin D consumed with diet, the body produces vitamin D when exposed to sunlight on the skin. With less daylight in the winter, people with SAD may have lower vitamin D levels, which may further hinder serotonin activity.
Negative thoughts and feelings about the winter and its associated limitations and stresses are common among people with SAD (as well as others). It is unclear whether these are "causes" or "effects" of the mood disorder, but they can be a useful focus of treatment.
How is SAD treated?
Treatments are available that can help many people with SAD. They fall into four main categories that may be used alone or in combination:
- Light therapy
- Antidepressant medications
- Vitamin D