In late fall, when the days get shorter, some people develop a special form of depression called seasonal affective disorder, or SAD. This condition should not be confused with mild winter blues. It is a real illness, as severely debilitating as any other form of clinical depression.

Symptoms are generally worst in January and February, and begin to disappear as the days lengthen in the spring. SAD occurs most often in adolescents and women, but it is not limited to those groups. Up to 25% of the population may suffer from a mild version of SAD, and perhaps 5% experience the full disorder.

The cause of SAD is not known, but is believed to relate to the daily biological clock and the way it responds to sunlight. The hormones melatonin and serotonin are thought to be involved, although exactly in what manner remains unclear.

Conventional treatment for SAD focuses on increasing exposure to light. Making sure to get outside during the brightest part of the day may help significantly. Bright artificial light sources (phototherapy) are also helpful. Antidepressant drugs may be used if these treatments prove ineffective.

Proposed Natural Treatments for Seasonal Affective Disorder

The body creates vitamin D when it is exposed to the sun, and during the winter vitamin D levels drop. For this reason, it seems logical that vitamin D supplements might help people with SAD. One double-blind, placebo-controlled trial conducted during winter on 44 people without seasonal affective disorder found that vitamin D supplements produced improvements in various measures of mood.1 However, a double-blind, placebo-controlled study of 2217 women over seventy failed to find benefit.12 It has been suggested that phototherapy for SAD works by raising vitamin D levels, but current evidence indicates that this hypothesis is incorrect.2

The hormone melatonin plays a major role in the daily biological clock. Our bodies are designed to manufacture melatonin at night, and stop making it when the sun comes out. One study found that people with SAD had higher levels of melatonin than those without the condition.3 On this basis, it would seem that supplemental melatonin should worsen SAD symptoms. However, the evidence for such an effect is inconsistent.4 Some researchers have proposed that interaction between SAD and melatonin might be more complex than merely high or low levels, and that, when taken at certain times of day, melatonin might help the condition. A very small study found that when melatonin was given in the afternoon, it produced some benefit for people with SAD.5 However, a study of melatonin used in the early morning or the late evening failed to find any benefit.6

A small study failed to find vitamin B12 helpful for SAD.7

The herb St. John’s wort has shown considerable promise for treating depression in general. However, the evidence that the herb is helpful for SAD consists only of studies too preliminary to prove much.8,9
Note: Combining St. John’s wort with bright light therapy might not be safe. A substance called hypericin, found in most St. John’s wort products, may cause the body to become hypersensitive to light, increasing risk of damage to the skin and eyes. See the full article on St. John’s wort for more information.

For reasons that are not at all clear, use of a device that produces negative ions may help SAD symptoms, according to two preliminary controlled studies.10,11