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Seasonal Affective Disorder

Seasonal affective disorder (SAD) is an extreme form of common seasonal mood cycles, in which depression develops during the winter months.

How seasonal changes cause depression is unknown, but most of the research into mechanisms and treatment has focused on changes in levels of the brain chemicals melatonin and serotonin in response to changing lengths of exposure to light and darkness.


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St. John’s wort


Vitamin D


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Contradictory, insufficient, or preliminary studies suggesting a health benefit or minimal health benefit.
For an herb, supported by traditional use but minimal or no scientific evidence. For a supplement, little scientific support and/or minimal health benefit.


What are the symptoms of seasonal affective disorder?

SAD is characterized by typical symptoms of depression, such as sadness, hopelessness, and thoughts of suicide (in some cases), and “atypical” depressive symptoms such as excessive sleep, lethargy, carbohydrate cravings, overeating, and weight gain. The symptoms usually occur the same time of year, typically fall and winter, and disappear with the onset of spring and summer.

Dietary changes that may be helpful for seasonal affective disorder

Cravings for simple carbohydrates are increased in SAD, and women diagnosed with this form of winter depression have been found to eat more carbohydrates, both sweets and starches, than do healthy women. These women also report eating in response to emotionally difficult conditions, anxiety, depression, and loneliness more frequently than healthy women, but eating patterns associated with SAD are distinct from those of women with eating disorders.1

People with SAD process sugar differently in winter compared with summer or after light therapy in winter.2 Changes in neurotransmitters that may affect cravings also occur in women with SAD.3 Because consumption of carbohydrates can influence neurotransmitter levels,4 some authorities have speculated that eating simple carbohydrates may be a form of self-medication in people with SAD. A review of the research on diet and mood found that, while eating simple carbohydrates in reaction to depressed mood does bring about a temporary lift in mood, other evidence suggests that long-term control of negative moods is, for some people, best achieved by eliminating simple carbohydrates from the diet.5 No research has yet been conducted, however, to evaluate the benefits of a diet low in simple carbohydrates (or any other dietary intervention) for people with SAD.

Lifestyle changes that may be helpful for seasonal affective disorder

Exercise can ease depression and improve well being, in some cases as effectively as antidepressant medications.6 One study found that both one hour of aerobic exercise three times per week and the same amount of anaerobic exercise were significantly and equally effective in reducing symptoms of depression.7 In a preliminary study of women with SAD, exercise while exposed to light was more likely to be associated with fewer seasonal depressive symptoms than was exercise performed with little light exposure.8 A controlled study of 120 indoor employees used relaxation training as the placebo in a study of fitness training, light exposure, and winter depressive symptoms. Fitness training was performed two to three times per week while exposed to either bright light (2,500–4,000 lux) or ordinary light (400–600 lux). Compared to relaxation, exercise in bright light improved general mental health, social functioning, depressive symptoms, and vitality, while exercise in ordinary light improved vitality only.

Nutritional supplements that may be helpful for seasonal affective disorder

L-tryptophan is the amino acid used by the body to manufacture serotonin. Several trials, some controlled, have shown that experimentally inducing a tryptophan deficiency in people with SAD who are in remission brings about a relapse of depressive symptoms.9 10 11 12 13 This suggests that supplemental L-tryptophan might be helpful in SAD. In small, preliminary trials, 4 to 6 grams of L-tryptophan given in divided amounts daily was as effective as light therapy14 15 and more effective than placebo.16 L-tryptophan may be of particular use in people with winter depression who do not benefit from light therapy. In a preliminary trial, people with SAD who responded only partially or not at all to bright light therapy were given 1,000 mg of L-tryptophan three times daily in addition to 10,000 lux light therapy for 30 minutes every morning. Sixty-four percent of them had significant improvement in depressive symptoms while receiving both L-tryptophan and bright light therapy.17 L-tryptophan is currently available by prescription only.

5-HTP is a substance related to L-tryptophan that increases serotonin production and has shown antidepressant activity.18 It may also be useful in the treatment of SAD, but there is currently no research testing this possibility.

Vitamin D is well known for its effects on helping to maintain normal calcium levels, but it also exerts influence on the brain, spinal cord, and hormone-producing tissues of the body that may be important in the regulation of mood.19 A double-blind controlled study found that mood improved in healthy people without SAD who received 400 or 800 IU per day of vitamin D for five days in late winter.20 However, no difference in vitamin D levels has been observed between people with seasonal depression and those without,21 22 and the antidepressant activity of light therapy has been shown to be independent of changes in levels of vitamin D.23 A large study of women found that supplementation with 400 IU per day of vitamin D had no impact on the incidence of winter depression.24 Any benefits of vitamin D on SAD remain unproven.

Depression can be one of the first symptoms of vitamin B12 deficiency.25 Vitamin B12, in the form of cyanocobalamin, given orally in the amount of 1,500 mcg three times daily to patients with seasonal depression, showed no superiority over placebo in a double-blind trial.26 Vitamin B12 cannot be recommended for the treatment of SAD.

Melatonin is a hormone produced in the body in response to the rhythms of light and darkness. Changes in melatonin levels are believed to be an important factor in seasonal depression. Supplementation with melatonin, however, has been ineffective when taken at night or in the morning.27 Melatonin may even reverse the benefits of light therapy in people with SAD.28 A small, double-blind study, however, found that 125 mcg of melatonin taken both 8 and 12 hours after awakening was effective for reducing depression’s symptoms.29

Are there any side effects or interactions with seasonal affective disorder?

Refer to the individual supplement for information about any side effects or interactions.

Herbs that may be helpful for seasonal affective disorder

St. John’s wort, an herb well known for its antidepressant activity,30 has been examined for its effectiveness in treating SAD. In a preliminary trial, patients with seasonal depression were given 900 mg per day of St. John’s wort in addition to either bright light (3,000 lux for two hours) or a dim light (300 lux for two hours) placebo.31 Both groups had significant improvement in depressive symptoms, but there was no difference between the groups. The authors concluded that St. John’s wort was beneficial with or without bright light therapy, but a placebo effect from the herb cannot be ruled out in this study. Another preliminary study asked 301 SAD patients to report the changes in their symptoms resulting from the use of St. John’s wort at 300 mg three times daily.32 Significant overall improvement was reported by these patients. Some of the subjects used light therapy in addition to St. John’s wort. They reported more improvement in sleep, but overall improvement was not significantly different from those using St. John’s wort alone. Double-blind research is needed to confirm the usefulness of St. John’s wort for treating SAD.

Are there any side effects or interactions with seasonal affective disorder?

Refer to the individual herb for information about any side effects or interactions.

Holistic approaches that may be helpful for seasonal affective disorder

Diminished sunlight exposure in winter contributes to changes in brain chemistry and plays a role in seasonal mood changes. Artificial lights have been widely used to increase light exposure during winter months. Many studies show the benefit of light therapy in the treatment of SAD.33 34 35 36 In a controlled trial, 96 patients with SAD were treated with light at 6,000 lux for 1.5 hours in either morning or evening, or with a sham negative ion generator, which was used as the placebo. After three weeks of treatment, morning light produced complete or near-complete remission for 61% of patients, while evening light helped 50%, and placebo helped 32%.37 Another study similarly found morning light to have more antidepressant activity than evening light for people with SAD. This study also found that patterns of melatonin production were altered in seasonal depression, and that morning light therapy shifted this pattern toward those of control subjects who did not have seasonal depression.38 Blood flow to certain regions of the brain was measured after light therapy and was increased in seasonal depression patients who benefited from the light therapy. The increase in regional brain blood flow did not occur in those patients who did not respond to the light therapy.39 Light therapy begun prior to the onset of winter depression appears to have a preventive effect in people susceptible to SAD.40

A review of clinical trials of light therapy for SAD concluded that the intensity of the light is related to the effectiveness of the treatmnent.41 A higher response rate was seen in trials where light intensity was greater, compared with trials that used light therapy of lower intensity. Red and potentially harmful ultraviolet wavelengths are not necessary for a response to light therapy.42

A study of the adverse side effects from high-intensity light therapy found them to be common, mild and brief. Among people who underwent brief treatment with 10,000 lux, 45% experienced side effects such as headaches and eye and vision changes. Described as mild and temporary, they did not interfere with treatment.43

Dawn simulation is a form of light therapy involving gradually increasing bedside light in the morning. In a comparison study, dawn simulation using 100–300 lux for 60–90 minutes every morning improved symptoms of SAD similarly to bright light therapy using 1,500–2,500 lux for two hours every morning.44

A negative ionizer is a device that emits negatively charged particles into the air. Negative air ionization may be useful in treating SAD. One double-blind trial compared the benefits of high-density negative ionization, providing 2.7 million ions per cubic centimeter, and low-density negative ionization, providing 10,000 ions per cubic centimeter, for people with SAD. Atypical depressive symptoms improved by 50% or more for 58% of patients receiving the high-density ionization for 30 minutes daily, while only 15% of those receiving low-density ionization had 50% or greater improvement. There were no side effects, and all of the patients who responded to the therapy relapsed when ionization was discontinued.45 In another controlled trial, high-density ionization was found equally as effective as light therapy, and both were significantly more effective than low-density ionization.46