[1][2] It is commonly, but not always, associated with the reductions or increases in total daily sunlight hours that occur during the winter or summer.
[6] The validity of SAD was called into question, however, by a 2016 analysis by the Centers for Disease Control in which no links were detected between depression and seasonality or sunlight exposure.
[8] SAD was formally described and named in 1984 by Norman E. Rosenthal and colleagues at the National Institute of Mental Health.
[9][10] SAD was first systematically reported and named in the early 1980s by Norman E. Rosenthal and his colleagues at the National Institute of Mental Health (NIMH).
The initial investigation was motivated by observations of depression occurring during the dark winter months in northern regions of the United States, known as polar night.
Although Rosenthal's ideas were initially greeted with skepticism, SAD has become well recognized, and his 1993 book Winter Blues[11] has become the standard introduction to the subject.
Kern suspected that scarcer natural light in winter was the cause and discussed the idea with NIMH scientists working on bodily rhythms.
[10][13] SAD is a type of major depressive disorder, and those with the condition may exhibit any of the associated symptoms, such as feelings of hopelessness and worthlessness, thoughts of suicide, loss of interest in activities, withdrawal from social interaction, sleep and appetite problems, difficulty with concentrating and making decisions, decreased libido, a lack of energy, or agitation.
[4] Symptoms of winter SAD often include falling asleep earlier or in less than 5 minutes in the evening, oversleeping or difficulty waking up in the morning, nausea, and a tendency to overeat, often with a craving for carbohydrates, which leads to weight gain.
[14] SAD is typically associated with winter depression, but springtime lethargy or other seasonal mood patterns are not uncommon.
[15] Although each individual case is different, in contrast to winter SAD, people who experience spring and summer depression may be more likely to show symptoms such as insomnia, decreased appetite and weight loss, and agitation or anxiety.
[17] A study by the National Institute of Health published findings in 2016 that concluded, "seasonal and circadian rhythm disturbances are significantly associated with ADHD symptoms."
[citation needed] Melatonin secretion is controlled by the endogenous circadian clock, but can also be suppressed by bright light.
Correlations between certain personality traits, higher levels of neuroticism, agreeableness, openness, and an avoidance-oriented coping style, appeared to be common in those with SAD.
A study published in May 2010 suggests that the blue light often used for SAD treatment should perhaps be replaced by green or white illumination.
[39] Most studies have found it effective without use year round, but rather as a seasonal treatment lasting for several weeks, until frequent light exposure is naturally obtained.
[24][45] Both fluoxetine and light therapy are 67% effective in treating SAD, according to direct head-to-head trials conducted during the 2006 Can-SAD study.
[47] In a 2021 updated Cochrane review of second-generation antidepressant medications for the treatment of SAD, a definitive conclusion could not be drawn, due to lack of evidence, and the need for larger randomized controlled trials.
[59] One particular study noted marked effectiveness for treatment of depressive symptoms, when combining regular exercise with bright light therapy.
[60] Patients exposed to exercise which had been added to their treatments in 20 minutes intervals on the aerobic bike during the day, along with the same amount of time underneath the UV light were seen to make a quick recovery.
[63] The study's authors suggested that propensity for SAD may differ due to some genetic factor within the Icelandic population.
[67][dubious – discuss] In the United States, a diagnosis of seasonal affective disorder was first proposed by Norman E. Rosenthal, M.D.