Melatonin cycles in Seasonal Affective Disorder.




Arch Gen Psychiatry

Related Monographs

Consumer Data: Melatonin Depression
Professional Data: Melatonin Depression


Depression affects approximately 5 percent of the population at any given time, and about 30 percent of adults will suffer from depression over a lifetime.1 Seasonal Affective Disorder (SAD) is depression that follows the change of seasons. The most common type is wintertime depression. Out of 100 people, 4 to 6 suffer from this depressive disorder.2 Most cases of SAD occur in women and as you age, the chances of getting this type of depression decrease. Many researchers believe that this is caused by the decrease of natural light seen in winter, which may explain why SAD is more prevalent in the north than the south.

Symptoms of this affective depression are headaches, weight gain, cravings for starches, fatigue, crying episodes, among others. Some factors that may cause SAD are stress, heredity, and chemical components in the body. The symptoms of major depression consistently reflect changes in "neurotransmitters," substances that regulate function of the brain and nervous system. The neurotransmitters closely related to depression are norepinephrine, serotonin, and dopamine.

In animals, the circadian rhythm adjusts to the seasonal changes. In the wintertime, animals have a longer nocturnal melatonin secretion, which is partially responsible for hibernation. A group of researchers investigated the circadian cycle in people that suffer from seasonal affective disorder. They measured the extent of melatonin secretion in dim light both in summer and winter. The melatonin levels were taken each half hour for 24 hours in each season. The subjects included 55 patients with SAD and 55 healthy controls. The results showed that the control subjects showed no change in the melatonin secretion. However, the patients' period of melatonin secretion was longer in the winter than in the summer, similar to animals' seasonal behavior changes. The authors concluded that patients of SAD produce a biological change in their body that healthy people do not.3


1. Richelson E. Treatment of Acute Depression. Psych Clin North Am. 1993;16:461-78.
2. American Academy of Family Physicians. SAD. 2000.
3. Wehr TA, et al. A Circadian Signal of Change of Season in Patients With Seasonal Affective Disorder. Arch Gen Psychiatry. Dec 2001;58:1108-1114.