SAD: A Seasonal Pattern
Circadian changes in the sleep system can lead to SAD.
Posted September 19, 2012
The American Psychiatric Association’s Diagnostic and Statistical Manual, the DSM, describes episodes of depression as having a “seasonal pattern” if the depression reoccurs repeatedly for at least two years and doesn’t occur at other times of the year. It can happen in winter or in summer, but must start and end at a characteristic time of the year.
As with all major depressive episodes, the seasonal type includes symptoms of depressed mood, loss of interest or pleasure in activities, decreased or increased appetite, insomnia or hypersomnia, fatigue, poor concentration, and possibly thoughts of death. Interestingly, there are additional typical symptoms of seasonal pattern depression, such as cravings for carbohydrates, weight gain, fatigue, difficulty concentrating, anxiety and social isolation, sleeping longer and difficulty getting up from bed. While SAD can occur in spring and summer, it is much less common than the fall onset type. As with any major depression, SAD can be debilitating and may require professional treatment, including medication and psychotherapy.
Men tend to have more severe symptoms of SAD, but it is more common among women. In addition to gender, other risk factors include having had past episodes of depression and a family history of seasonal pattern depression.
Not everyone who has seasonal depression experiences a full major depressive episode. More common is the “winter blues." While not as severe as SAD, people with the winter blues also have low mood, cravings for carbohydrates, difficulty getting up, and are easily exhausted. While their symptoms may be less debilitating and may not result in the need for professional treatment, they find fall and winter are to be endured, not enjoyed. Such people may experience the upcoming fall and winter with dread, and may fantasize about moving to southern California. New England is not often a comfortable home for people with the winter blues.
The causes of SAD and winter blues is unknown. Some evidence, however, links these conditions to changes in the sleep system brought about by seasonal changes in light levels. As the days get shorter, the circadian system that regulates the 24 hour sleep/wake cycle may become disrupted, similar to changes that occur with jet lag or shift work. The disruption in the circadian regulation of sleep may then result in low mood or full major depression. Serotonin levels may be decreased by lower levels of light in the fall and winter. Decreased levels of serotonin have been associated with depressed mood. In addition, changes in light levels may also disrupt melatonin levels, which are affected by light.
The circadian system needs to be reset daily by synchronizing with external events such as activity levels, meals, and bright light. Light is the most effective time synchronizing factor and there are receptors in the retina to allow the brain to know what time of day it is based on light levels. Melatonin is released by the pineal gland as it starts to get dark outside and affects a specific nucleus of the brain that sets the circadian rhythm. Drowsiness follows the release of melatonin. When we are exposed to bright light we find it harder to feel sleepy and drift off to sleep. Bright lights in hospital halls and factory floors help those working through the night stay awake. Think how much harder a detective’s “stakeout” is when sitting in a dark car at night than when doing the same during daylight hours. It’s much harder to remain alert after dark.
People seem to function best when they sleep for eight hours and be alert for 16 of the 24 hours that make up the day. If you live near the equator, the amount of daylight remains relatively constant throughout the year. Further north, in places such as New England or Alaska, the length of daylight varies depending on the season. As the days grow short, light decreases and the sleep/wake system may not be able to function optimally. Depression can occur as the sleep system gets unbalanced.
In the next blog I will discuss some treatment approaches for dealing with seasonal depression. Unsurprisingly, these approaches are closely related to better regulating the sleep system!