Seasonal Affective Disorder (SAD) is a major form of depression that occurs at the same time each year. Most people who suffer from this disorder experience the strongest symptoms during the winter (particularly during the months of December, January and February), but others have worse symptoms during the summer months. The Cleveland Clinic estimates that four-to-six percent of the general population experience SAD, with women outnumbering men four-to-one.

According to the National Mental Health Association (NMHA), SAD was first noted before 1845, although it was not named until the early 1980s. When people became aware that sunlight had an effect on the seasonal activities of animals (such as hibernation), many began to wonder if sunlight and seasonal light variation had the same effect on humans. It turns out that as seasons change, our circadian rhythm (or biological clock) shifts due to changes in sunlight pattern.

What Causes SAD?

Although the exact cause of SAD is unknown, there are many theories as to what causes this disorder. According to the National Organization for Seasonal Affective Disorder (NOSAD), for most people, SAD is caused by a biochemical imbalance in the hypothalamus due to the shortening of daylight hours and the lack of sunlight in the winter. Moreover, research has shown that SAD is becoming increasingly more common the farther north or south people live from the equator, with symptoms being more severe for people living at higher latitudes.

The NMHA reports that melatonin (a sleep-related hormone) may also be a contributing factor to SAD. Melatonin, which has been linked to symptoms of depression, is produced at increased levels in the dark. When the days are shorter and darker, the production of the hormone increases.

Symptoms

According to the Cleveland Clinic, SAD symptoms generally develop in a person’s early 20s; and the risk for developing SAD decreases with age. For many people, SAD is a major illness that prevents them from functioning normally without having to undergo continuous treatment. For others, it is a milder condition that causes slight discomfort and is also known as winter blues. Many of the symptoms of SAD are similar to that of any depressive disorder but do not happen year-round; they may include:

• The desire to oversleep: People who suffer from winter depression will have a difficult time staying awake and constantly feel tired during the winter months. For those who suffer from summer depression, it is the other way around.
• Feeling fatigued: Individuals feel as if they can’t carry out a normal routine.
• Cravings for carbohydrates: Many people suffering from SAD will crave sweets and other sugary and starchy foods, which often leads to weight gain.
• Feelings of misery: SAD sufferers may feel a lot of guilt and have low self-esteem. Often times they will feel a sense of hopelessness and despair; other times, apathy and loss of feelings.
• Interpersonal difficulties: Individuals tend to have trouble communicating and having effective relationships with those who are close.
• Irritability: People with SAD may have no desire to be around others and try to avoid social situations.
• Tension: This often results from an overload of stress and the inability to tolerate it.
• Decreased interest: SAD sufferers may lose interest in activities that they once enjoyed (such as sex and physical contact).
• Mood extremes: When people suffer from winter depression, for example, they may have short periods of hypomania (over activity) during the spring and summer months.  Likewise, those with summer depression experience periods of over activity during the winter months.
• Full remission in the opposite season: Symptoms often lessen or may even disappear in the opposite seasons. Individuals may have no nonseasonal depression episodes during these months.

Sources: National Mental Health Association; National Organization for Seasonal Affective Disorder; The Cleveland Clinic