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Seasonal Affective Disorder

Seasonal affective disorder (SAD) is a subset of mood disorders in which individuals with typically normal mental health experience depressive symptoms at the same time each year. This condition is often associated with the changes in daily sunlight hours during summer or winter. Common symptoms include oversleeping, low energy, and overeating, with heightened anxiety in some cases during summer.

Bright light therapy is a common treatment for seasonal affective disorder and for circadian rhythm sleep disorders.
Bright light therapy is a common treatment for seasonal affective disorder and for circadian rhythm sleep disorders.


SAD was first systematically reported in the early 1980s by Norman E. Rosenthal and his colleagues at the National Institute of Mental Health (NIMH). Rosenthal hypothesised that the reduction in natural light during winter was the cause of his own winter depression. His placebo-controlled study using light therapy documented the phenomenon, leading to the publication of a paper in 1984. Despite initial scepticism, SAD became well-recognised, with Rosenthal's book, Winter Blues, serving as a standard introduction.

Herb Kern, a research engineer, also noticed his depression during winter and collaborated with NIMH scientists, leading to the development of a lightbox treatment. Kern and other patients experienced significant improvements with this therapy.

Signs and Symptoms

SAD is a type of major depressive disorder, with symptoms such as feelings of hopelessness, worthlessness, thoughts of suicide, loss of interest in activities, social withdrawal, sleep and appetite problems, difficulty concentrating, decreased libido, lack of energy, and agitation. Winter SAD often includes oversleeping, difficulty waking up, nausea, and overeating, leading to weight gain. Conversely, summer SAD may involve insomnia, decreased appetite, weight loss, and increased anxiety.

Bipolar Disorder

With seasonal pattern is a specifier for bipolar and related disorders, where individuals may experience depressive episodes during winter and remission in summer. About 20% of people with SAD have a bipolar disorder. Differences in biological sex present distinct characteristics: males often have more Bipolar II disorder and depressive episodes, while females may exhibit rapid cycling and eating disorders.


SAD may be related to evolutionary adaptations, with activity diminishing during winter due to reduced food, sunlight, and harsh weather conditions. The prevalence of SAD in women suggests a link to reproductive regulation. Possible causes include a lack of serotonin or melatonin, with research indicating that light therapy can correct circadian rhythm delays. Certain personality traits, such as higher levels of neuroticism, agreeableness, and openness, along with an avoidance-oriented coping style, may predispose individuals to SAD.


Light is believed to play a very important role in seasonal mood variations, supported by the effectiveness of bright-light therapy. SAD is prevalent at higher latitudes, with a 9.5% rate in northern Finland. Cloud cover may exacerbate symptoms. Patients often exhibit circadian rhythm delays, which light therapy can correct, improving their condition.


The American Psychiatric Association's DSM-IV does not regard SAD as a separate disorder, but as a course specifier for major depressive and bipolar disorders. The "Seasonal Pattern Specifier" requires depressive episodes at a specific time of year, remission or mania/hypomania at a characteristic time, a two-year pattern without nonseasonal depressive episodes, and more seasonal than nonseasonal depressive episodes throughout the patient's life.


Treatment for winter SAD includes light therapy, medication, ionised-air administration, cognitive-behavioural therapy, and melatonin supplementation.

Light Therapy

Photoperiod-related alterations in melatonin secretion suggest light therapy's effectiveness. It involves using a lightbox emitting bright white, blue, or green light at prescribed distances and durations. Dawn simulation is also effective, with 83% better response rates compared to other bright light therapies. Patients may experience improvement in one week, with continued benefits over several weeks. Sunlight exposure or heliostats can also help, but prolonged UV exposure should be avoided due to skin cancer risks.


SSRIs like fluoxetine, sertraline, and paroxetine are effective for treating SAD, with fluoxetine and light therapy showing 67% effectiveness. Bupropion extended-release can prevent SAD in some individuals. Modafinil may also be effective. Vitamin D supplementation, 5-HTP, and physical exercise are other potential treatments.

Other Treatments

Negative air ionisation, physical exercise, and cognitive-behavioural therapy (CBT) have shown effectiveness in treating SAD. Combining treatments, such as light therapy with exercise, can enhance recovery.


Nordic Countries

Winter depression is common in Nordic countries, but Iceland has a low prevalence, possibly due to genetic factors or high fish consumption, which provides vitamin D and DHA.

Other Countries

In the United States, SAD was first proposed by Norman E. Rosenthal in 1984. Alaska has an 8.9% SAD rate, with 24.9% for subsyndromal SAD. In Ireland, 20% of people are affected, with women more likely to experience SAD. In the Netherlands, 3% of people experience winter SAD.

Self-assessment MCQs (single best answer)

Who first systematically reported Seasonal Affective Disorder (SAD) in the early 1980s?

Which therapy is commonly used to treat Seasonal Affective Disorder?

Which of the following symptoms is more commonly associated with winter SAD than summer SAD?

What percentage of people with Seasonal Affective Disorder (SAD) have a bipolar disorder?

Which personality trait is NOT mentioned as a predisposing factor for SAD?

In which country is the prevalence of SAD particularly high, with a 9.5% rate reported?

Which of the following is NOT a common treatment for winter SAD?

What is the specifier used in the DSM-IV for SAD within the context of major depressive and bipolar disorders?

What dietary factor is suggested to contribute to the low prevalence of SAD in Iceland?

Which medication is mentioned as effective in preventing SAD in some individuals?


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