Seasonal affective disorder
|Seasonal affective disorder|
|Bright light therapy is a common treatment for seasonal affective disorder and for circadian rhythm sleep disorders.|
|Classification and external resources|
|Patient UK||Seasonal affective disorder|
Seasonal affective disorder (SAD), also called winter depression, winter blues, summer depression, and seasonal depression, is a mood disorder subset in which people who have normal mental health throughout most of the year exhibit depressive symptoms at the same time each year, most commonly in the winter.
In the Diagnostic and Statistical Manual of Mental Disorders DSM-IV and DSM-5, its status was changed. It is no longer classified as a unique mood disorder but is now a specifier, called with seasonal pattern, for recurrent major depressive disorder that occurs at a specific time of the year and fully remits otherwise. Although experts were initially skeptical, this condition is now recognized as a common disorder. SAD's prevalence in the U.S. ranges from 1.4% in Florida to 9.9% in Alaska.
The U.S. National Library of Medicine notes that "some people experience a serious mood change when the seasons change. They may sleep too much, [may] have little energy, and may also feel depressed. Though symptoms can be severe, they usually clear up." The condition in the summer can include heightened anxiety.
There are many treatments for classic (winter-based) seasonal affective disorder.
Signs and symptoms
SAD is a type of major depressive disorder, and sufferers 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 concentration and decisions, decreased sex drive, a lack of energy, or agitation. Symptoms of winter SAD often include oversleeping or difficulty waking up in the morning, nausea, and a tendency to over eat, often with a craving for carbohydrates, which leads to weight gain. SAD is typically associated with winter depression, but springtime lethargy or other seasonal mood patterns are not uncommon. 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.
With seasonal pattern is a specifier for bipolar and related disorders, including bipolar I disorder and bipolar II disorder. Most people with SAD experience major depressive disorder, but as many as 20% may have a bipolar disorder. It is important to discriminate between diagnoses because there are important treatment differences. In these cases, people who have the With seasonal pattern specifier may experience a major depression or bipolar disorder during the winter and remit in the summer. Around 25% of patients with bipolar disorder may present with a depressive seasonal pattern, which is associated with bipolar II disorder, rapid cycling, eating disorders, and more depressive episodes. Gender displays distinct clinical characteristics associated to seasonal pattern: males present with more Bipolar II disorder and a higher number of depressive episodes, and females with rapid cycling and eating disorders.
In many species, activity is diminished during the winter months in response to the reduction in available food, the reduction of sunlight (especially for diurnal animals) and the difficulties of surviving in cold weather. Hibernation is an extreme example, but even species that do not hibernate often exhibit changes in behavior during the winter. Presumably, food was scarce during most of human prehistory, and a tendency toward low mood during the winter months would have been adaptive by reducing the need for calorie intake. The preponderance of women with SAD suggests that the response may also somehow regulate reproduction.
Various proximate causes have been proposed. One possibility is that SAD is related to a lack of serotonin, and serotonin polymorphisms could play a role in SAD, although this has been disputed. Mice incapable of turning serotonin into N-acetylserotonin (by serotonin N-acetyltransferase) appear to express "depression-like" behavior, and antidepressants such as fluoxetine increase the amount of the enzyme serotonin N-acetyltransferase, resulting in an antidepressant-like effect. Another theory is that the cause may be related to melatonin which is produced in dim light and darkness by the pineal gland, since there are direct connections, via the retinohypothalamic tract and the suprachiasmatic nucleus, between the retina and the pineal gland. Melatonin secretion is controlled by the endogenous circadian clock, but can also be suppressed by bright light.
One study looked at whether some people could be predisposed to SAD based on personality traits. 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.
According to the American Psychiatric Association DSM-IV criteria, Seasonal Affective Disorder is not regarded as a separate disorder. It is called a "course specifier" and may be applied as an added description to the pattern of major depressive episodes in patients with major depressive disorder or patients with bipolar disorder.
The "Seasonal Pattern Specifier" must meet four criteria: depressive episodes at a particular time of the year; remissions or mania/hypomania at a characteristic time of year; these patterns must have lasted two years with no nonseasonal major depressive episodes during that same period; and these seasonal depressive episodes outnumber other depressive episodes throughout the patient's lifetime. The Mayo Clinic describes three types of SAD, each with its own set of symptoms.
Seasonal mood variations are believed to be related to light. An argument for this view is the effectiveness of bright-light therapy. SAD is measurably present at latitudes in the Arctic region, such as northern Finland (64°00′N), where the rate of SAD is 9.5%. Cloud cover may contribute to the negative effects of SAD. There is evidence that many patients with SAD have a delay in their circadian rhythm, and that bright light treatment corrects these delays which may be responsible for the improvement in patients.
The symptoms of it mimic those of dysthymia or even major depressive disorder. There is also potential risk of suicide in some patients experiencing SAD. One study reports 6–35% of sufferers required hospitalization during one period of illness. At times, patients may not feel depressed, but rather lack energy to perform everyday activities.
Subsyndromal Seasonal Affective Disorder is a milder form of SAD experienced by an estimated 14.3% (vs. 6.1% SAD) of the U.S. population. The blue feeling experienced by both SAD and SSAD sufferers can usually be dampened or extinguished by exercise and increased outdoor activity, particularly on sunny days, resulting in increased solar exposure. Connections between human mood, as well as energy levels, and the seasons are well documented, even in healthy individuals.
Treatments for classic (winter-based) seasonal affective disorder include light therapy, medication, ionized-air administration, cognitive-behavioral therapy and carefully timed supplementation of the hormone melatonin.
Photoperiod-related alterations of the duration of melatonin secretion may affect the seasonal mood cycles of SAD. This suggests that light therapy may be an effective treatment for SAD. Light therapy uses a lightbox which emits far more lumens than a customary incandescent lamp. Bright white "full spectrum" light at 10,000 lux, blue light at a wavelength of 480 nm at 2,500 lux or green (actually cyan or blue-green) light at a wavelength of 500 nm at 350 lux are used, with the first-mentioned historically preferred.
Bright light therapy is effective with the patient sitting a prescribed distance, commonly 30–60 cm, in front of the box with her/his eyes open but not staring at the light source for 30–60 minutes. 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. Discovering the best schedule is essential. One study has shown that up to 69% of patients find lightbox treatment inconvenient and as many as 19% stop use because of this.
Dawn simulation has also proven to be effective; in some studies, there is an 83% better response when compared to other bright light therapy. When compared in a study to negative air ionization, bright light was shown to be 57% effective vs. dawn simulation 50%. Patients using light therapy can experience improvement during the first week, but increased results are evident when continued throughout several weeks. 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.
Light therapy can also consist of exposure to sunlight, either by spending more time outside or using a computer-controlled heliostat to reflect sunlight into the windows of a home or office. Although light therapy is the leading treatment for seasonal affective disorder, prolonged direct sunlight or artificial lights that don't block the ultraviolet range should be avoided due to the threat of skin cancer.
SSRI (selective serotonin reuptake inhibitor) antidepressants have proven effective in treating SAD. Effective antidepressants are fluoxetine, sertraline, or paroxetine. 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. Subjects using the light therapy protocol showed earlier clinical improvement, generally within one week of beginning the clinical treatment. Bupropion extended-release has been shown to prevent SAD for one in eight people, but has not been compared directly to other preventive options in trials.
Negative air ionization, which involves releasing charged particles into the sleep environment, has been found effective with a 47.9% improvement if the negative ions are in sufficient density (quantity).
Depending upon the patient, one treatment (e.g., lightbox) may be used in conjunction with another (e.g., medication).
Another explanation is that vitamin D levels are too low when people do not get enough Ultraviolet-B on their skin. An alternative to using bright lights is to take vitamin D supplements. However, studies did not show a link between vitamin D levels and depressive symptoms in elderly Chinese nor among elderly British women.
Physical exercise has shown to be an effective form of depression therapy, particularly when in addition to another form of treatment for SAD. One particular study noted marked effectiveness for treatment of depressive symptoms when combining regular exercise with bright light therapy. 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 quick recovery.
Winter depression is a common slump in the mood of some inhabitants of most of the Nordic countries. It was first described by the 6th century Goth scholar Jordanes in his Getica wherein he described the inhabitants of Scandza (Scandinavia). Iceland, however, seems to be an exception. A study of more than 2000 people there found the prevalence of seasonal affective disorder and seasonal changes in anxiety and depression to be unexpectedly low in both sexes. The study's authors suggested that propensity for SAD may differ due to some genetic factor within the Icelandic population. A study of Canadians of wholly Icelandic descent also showed low levels of SAD. It has more recently been suggested that this may be attributed to the large amount of fish traditionally eaten by Icelandic people, in 2007 about 90 kilograms per person per year as opposed to about 24 kg in the US and Canada, rather than to genetic predisposition; a similar anomaly is noted in Japan, where annual fish consumption in recent years averages about 60 kg per capita.
In the United States, a diagnosis of seasonal affective disorder was first proposed by Norman E. Rosenthal, M.D. in 1984. Rosenthal wondered why he became sluggish during the winter after moving from sunny South Africa to (cloudy in winter) New York. He started experimenting increasing exposure to artificial light, and found this made a difference. In Alaska it has been established that there is a SAD rate of 8.9%, and an even greater rate of 24.9% for subsyndromal SAD.
Around 20% of Irish people are affected by SAD, according to a survey conducted in 2007. The survey also shows women are more likely to be affected by SAD than men. An estimated 10% of the population in the Netherlands suffer from SAD.
SAD was first systematically reported and named in the early 1980s by Norman E. Rosenthal, M.D., and his associates at the National Institute of Mental Health (NIMH). Rosenthal was initially motivated by his desire to discover the cause of his own experience of depression during the dark days of the northern US winter. He theorized that the reduction in available natural light during winter was the cause. Rosenthal and his colleagues then documented the phenomenon of SAD in a placebo-controlled study utilizing light therapy. A paper based on this research was published in 1984. Although Rosenthal's ideas were initially greeted with skepticism, SAD has become well recognized, and his 1993 book, Winter Blues has become the standard introduction to the subject.
Research on SAD in the United States began in 1979 when Herb Kern, a research engineer, had also noticed that he felt depressed during the winter months. Kern suspected that scarcer light in winter was the cause and discussed the idea with scientists at the NIMH who were working on bodily rhythms. They were intrigued, and responded by devising a lightbox to treat Kern’s depression. Kern felt much better within a few days of treatments, as did other patients treated in the same way.
It has been also suggested that SAD affects risky behavior, and those affected by SAD are more likely to opt for conservative investments, whether financially or scientifically.
- Oginska, Halszka; Oginska-Bruchal, Katarzyna (2014). "Chronotype And Personality Factors Of Predisposition To Seasonal Affective Disorder". Chronobiology International: The Journal Of Biological & Medical Rhythm Research. 31 (4): 523–531. doi:10.3109/07420528.2013.874355.
- Ivry, Sara (August 13, 2002). Seasonal Depression can Accompany Summer Sun. The New York Times. Retrieved September 6, 2008
- Friedman, Richard A. (December 18, 2007) Brought on by Darkness, Disorder Needs Light. New York Times’’.
- Nolen-Hoeksema, Susan (2014). Abnormal Psychology (6th ed.). New York, New York: McGraw-Hill Education. p. 179. ISBN 978-1-259-06072-4.
- MedlinePlus Overview seasonalaffectivedisorder
- Seasonal affective disorder (SAD): Symptoms. MayoClinic.com (September 22, 2011). Retrieved on March 24, 2013.
- Rosenthal, N. E.; Sack, D. A.; Gillin, J. C.; Lewy, A. J.; Goodwin, F. K.; Davenport, Y.; Mueller, P. S.; Newsome, D. A.; Wehr, T. A. (1984). "Seasonal affective disorder. A description of the syndrome and preliminary findings with light therapy". Archives of General Psychiatry. 41 (1): 72–80. PMID 6581756. doi:10.1001/archpsyc.1984.01790120076010.
- Marshall, Fiona. Cheevers, Peter (2003). "Positive options for Seasonal Affective Disorder", p. 77. Hunter House, Alameda, Calif. ISBN 0-89793-413-X.
- Partonen, Dr. Timo (1998). "Seasonal affective disorder". The Lancet. 352 (9137): 1369–1374. doi:10.1016/s0140-6736(98)01015-0.
- "Depression" (PDF). Mood Disorders Society of Canada. Retrieved August 8, 2009.
- Geoffroy PA; Bellivier F; Scott J; Boudebesse C; Lajnef M; Gard S; Kahn JP; Azorin JM; Henry C; Leboyer M; Etain B. (Aug 2013). "Bipolar Disorder with Seasonal Pattern: Clinical Characteristics and Gender Influences.". Chronobiol Int. 30 (9): 1101–7. PMC . PMID 23931033. doi:10.3109/07420528.2013.800091.
- Nesse, Randolph M; Williams, George C (1996). Why We Get Sick (First ed.). New York: Vintage Books. ISBN 0812922247.
- Kalbitzer, J.; Kalbitzer, U.; Moos Knudsen, G.; Cumming, P.; Heinz, A. (2013). "How the cerebral serotonin homeostasis predicts environmental changes: a model to explain seasonal changes of brain 5-HTT as intermediate phenotype of the 5-HTTLPR". Psychopharmacology (Berlin). 230 (3): 333–343. PMID 24150247. doi:10.1007/s00213-013-3308-1.
- Johansson, C.; Smedh, C.; Partonen, T.; Pekkarinen, P.; Paunio, T.; Ekholm, J.; Peltonen, L.; Lichtermann, D.; Palmgren, J.; Adolfsson, R.; Schalling, M. (2001). "Seasonal Affective Disorder and Serotonin-Related Polymorphisms". Neurobiology of Disease. 8 (2): 351–357. PMID 11300730. doi:10.1006/nbdi.2000.0373.
- Johansson, C.; Willeit, M.; Levitan, R.; Partonen, T.; Smedh, C.; Del Favero, J.; Bel Kacem, S.; Praschak-Rieder, N.; Neumeister, A.; Masellis, M.; Basile, V.; Zill, P.; Bondy, B.; Paunio, T.; Kasper, S.; Van Broeckhoven, C.; Nilsson, L. -G.; Lam, R.; Schalling, M.; Adolfsson, R. (2003). "The serotonin transporter promoter repeat length polymorphism, seasonal affective disorder and seasonality". Psychological Medicine. 33 (5): 785–792. PMID 12877393. doi:10.1017/S0033291703007372.
- Uz, T.; Manev, H. (2001). "Prolonged swim-test immobility of serotonin N-acetyltransferase (AANAT)-mutant mice". Journal of Pineal Research. 30 (3): 166–170. PMID 11316327. doi:10.1034/j.1600-079X.2001.300305.x.
- Lam, R. W.; Levitan, R. D. (2000). "Pathophysiology of seasonal affective disorder: A review". Journal of psychiatry & neuroscience : JPN. 25 (5): 469–480. PMC . PMID 11109298.
- Gabbard, Glen O. Treatment of Psychiatric Disorders. 2 (3rd ed.). Washington, DC: American Psychiatric Publishing. p. 1296.
- Lam, R. W.; Levitt, A. J.; Levitan, R. D.; Enns, M. W.; Morehouse, R.; Michalak, E. E.; Tam, E. M. (2006). "The Can-SAD Study: A Randomized Controlled Trial of the Effectiveness of Light Therapy and Fluoxetine in Patients with Winter Seasonal Affective Disorder". American Journal of Psychiatry. 163 (5): 805–812. PMID 16648320. doi:10.1176/appi.ajp.163.5.805.
- Avery, D. H.; Eder, D. N.; Bolte, M. A.; Hellekson, C. J.; Dunner, D. L.; Vitiello, M. V.; Prinz, P. N. (2001). "Dawn simulation and bright light in the treatment of SAD: A controlled study". Biological Psychiatry. 50 (3): 205–216. PMID 11513820. doi:10.1016/S0006-3223(01)01200-8.
- Modell, J. G.; Rosenthal, N. E.; Harriett, A. E.; Krishen, A.; Asgharian, A.; Foster, V. J.; Metz, A.; Rockett, C. B.; Wightman, D. S. (2005). "Seasonal Affective Disorder and Its Prevention by Anticipatory Treatment with Bupropion XL". Biological Psychiatry. 58 (8): 658–667. PMID 16271314. doi:10.1016/j.biopsych.2005.07.021.
- Avery, D. H.; Kizer, D.; Bolte, M. A.; Hellekson, C. (2001). "Bright light therapy of subsyndromal seasonal affective disorder in the workplace: Morning vs. Afternoon exposure". Acta Psychiatrica Scandinavica. 103 (4): 267–274. PMID 11328240. doi:10.1034/j.1600-0447.2001.00078.x.
- Leppämäki, S.; Haukka, J.; Lönnqvist, J.; Partonen, T. (2004). "Drop-out and mood improvement: A randomised controlled trial with light exposure and physical exercise ISRCTN36478292". BMC Psychiatry. 4: 22. PMC . PMID 15306031. doi:10.1186/1471-244X-4-22.
- Partonen, Timo; Lönnqvist, Jouko (2000). "Bright light improves vitality and alleviates distress in healthy people". Journal of Affective Disorders. 57 (1–3): 55–61. doi:10.1016/S0165-0327(99)00063-4.
- Terman, M.; Terman, J. S. (2006). "Controlled Trial of Naturalistic Dawn Simulation and Negative Air Ionization for Seasonal Affective Disorder". American Journal of Psychiatry. 163 (12): 2126–33. PMID 17151164. doi:10.1176/appi.ajp.163.12.2126.
- Bhattacharjee, Y. (2007). "Is Internal Timing Key to Mental Health?". Science. 317 (5844): 1488–1490. PMID 17872420. doi:10.1126/science.317.5844.1488.
- "Properly Timed Light, Melatonin Lift Winter Depression by Syncing Rhythms". NIMH Science News. The National Institute of Mental Health (NIMH). 1 May 2006. Retrieved 9 December 2014.
- Howland, R. H. (2009). "Somatic therapies for seasonal affective disorder". Journal of psychosocial nursing and mental health services. 47 (1): 17–20. PMID 19227105. doi:10.3928/02793695-20090101-07.
- Zimmerman Jones, Andrew (February 15, 2012). "The Visible Light Spectrum".
- Saeeduddin Ahmed, Neil L Cutter, Alfred J. Lewy, Vance K. Bauer, Robert L Sack and Mary S. Cardoza (1995). "Phase Response Curve of Low-Intensity Green Light in Winter Depressives". Sleep Research. 24: 508. doi:10.1186/1471-244X-5-42.
The magnitude of the phase shifts [using low-level green light therapy] are comparable to those obtained using high-intensity white light in winter-depressives.
- Strong, R. E.; Marchant, B. K.; Reimherr, F. W.; Williams, E.; Soni, P.; Mestas, R. (2009). "Narrow-band blue-light treatment of seasonal affective disorder in adults and the influence of additional nonseasonal symptoms". Depression and Anxiety. 26 (3): 273–278. PMID 19016463. doi:10.1002/da.20538.
- Gooley, J. J.; Rajaratnam, S. M. W.; Brainard, G. C.; Kronauer, R. E.; Czeisler, C. A.; Lockley, S. W. (2010). "Spectral Responses of the Human Circadian System Depend on the Irradiance and Duration of Exposure to Light". Science Translational Medicine. 2 (31): 31ra33. PMC . PMID 20463367. doi:10.1126/scitranslmed.3000741.
- Beck, Melinda. (December 1, 2009) "Bright Ideas for Treating the Winter Blues". (Section title: "Exercise outdoors") The Wall Street Journal.
- "Applications: Health". Practical Solar. Retrieved June 9, 2009.
- "Grab the Sun With Heliostats". New York House. June 1, 2009. Retrieved December 8, 2009.
- Osborn, J.; Raetz, J.; Kost, A. (2014). "Seasonal Affective Disorder, Grief Reaction, and Adjustment Disorder". Medical Clinics of North America. 98 (5): 1065–1077. doi:10.1016/j.mcna.2014.06.006.
- Moscovitch, A.; Blashko, C. A.; Eagles, J. M.; Darcourt, G.; Thompson, C.; Kasper, S.; Lane, R. M.; International Collaborative Group on Sertraline in the Treatment of Outpatients with Seasonal Affective Disorders (2004). "A placebo-controlled study of sertraline in the treatment of outpatients with seasonal affective disorder". Psychopharmacology. 171 (4): 390–397. PMID 14504682. doi:10.1007/s00213-003-1594-8.
- Lam, Raymond W.; Anthony J. Levitt; Robert D. Levitan; et al. (May 2006). "The Can-SAD Study: A Randomized Controlled Trial of the Effectiveness of Light Therapy and Fluoxetine in Patients With Winter Seasonal Affective Disorder" (PDF). Am J Psychiatry. 163 (5): 805–812. PMID 16648320. doi:10.1176/appi.ajp.163.5.805.
- Gartlehner, Gerald; et al. (2015). "Second-generation antidepressants for preventing seasonal affective disorder in adults.". Cochrane Database Syst Rev. 11 (11): CD011268. PMID 26558418. doi:10.1002/14651858.CD011268.pub2. Retrieved 19 November 2015.
- Terman, M.; Terman, J.; Ross, D. (1998). "A Controlled Trial of Timed Bright Light and Negative Air Ionization for Treatment of Winter Depression". Archives of General Psychiatry. 55 (10): 875–82. PMID 9783557. doi:10.1001/archpsyc.55.10.875.
- Terman, M.; Terman, J. S. (1995). "Treatment of seasonal affective disorder with a high-output negative ionizer". Journal of alternative and complementary medicine. 1 (1): 87–92. PMID 9395604. doi:10.1089/acm.1995.1.87.
- Lundt, L. (2004). "Modafinil treatment in patients with seasonal affective disorder/winter depression: An open-label pilot study". Journal of Affective Disorders. 81 (2): 173–178. PMID 15306145. doi:10.1016/S0165-0327(03)00162-9.
- SADness: Seasonal Affective Disorder & Vitamin D. newfoundlandnews.blogspot.com (January 27, 2008)
- Wilkins, C. H.; Sheline, Y. I.; Roe, C. M.; Birge, S. J.; Morris, J. C. (2006). "Vitamin D Deficiency is Associated with Low Mood and Worse Cognitive Performance in Older Adults". American Journal of Geriatric Psychiatry. 14 (12): 1032–1040. PMID 17138809. doi:10.1097/01.JGP.0000240986.74642.7c.
- Lansdowne, A. T.; Provost, S. C. (1998). "Vitamin D3 enhances mood in healthy subjects during winter". Psychopharmacology. 135 (4): 319–323. PMID 9539254. doi:10.1007/s002130050517.
- Gloth Fm, 3.; Alam, W.; Hollis, B. (1999). "Vitamin D vs broad spectrum phototherapy in the treatment of seasonal affective disorder". The journal of nutrition, health & aging. 3 (1): 5–7. PMID 10888476.
- "Vitamin D May Not Be The Answer To Feeling SAD". sciencedaily.com (March 2009)
- Dumville, J. C.; Miles, J. N.; Porthouse, J.; Cockayne, S.; Saxon, L.; King, C. (2006). "Can vitamin D supplementation prevent winter-time blues? A randomised trial among older women". The journal of nutrition, health & aging. 10 (2): 151–153. PMID 16554952.
- Pinchasov, B. B.; Shurgaja, A. M.; Grischin, O. V.; Putilov, A. A. (2000). "Mood and energy regulation in seasonal and non-seasonal depression before and after midday treatment with physical exercise or bright light". Psychiatry Research. 94 (1): 29–42. PMID 10788675. doi:10.1016/S0165-1781(00)00138-4.
- Leppämäki, S.; Partonen, T.; Lönnqvist, J. (2002). "Bright-light exposure combined with physical exercise elevates mood". Journal of Affective Disorders. 72 (2): 139–144. PMID 12200204. doi:10.1016/S0165-0327(01)00417-7.
- Roecklein, K. A.; Rohan, K. J. (2005). "Seasonal affective disorder: An overview and update". Psychiatry (Edgmont (Pa. : Township)). 2 (1): 20–26. PMC . PMID 21179639.
- Jordanes, Getica, ed. Mommsen, Mon. Germanae historica, V, Berlin, 1882.
- Magnusson, A.; Axelsson, J.; Karlsson, M. M.; Oskarsson, H. (2000). "Lack of seasonal mood change in the Icelandic population: Results of a cross-sectional study". The American Journal of Psychiatry. 157 (2): 234–238. PMID 10671392. doi:10.1176/appi.ajp.157.2.234.
- Magnússon, A.; Axelsson, J. (1993). "The prevalence of seasonal affective disorder is low among descendants of Icelandic emigrants in Canada". Archives of General Psychiatry. 50 (12): 947–951. PMID 8250680. doi:10.1001/archpsyc.1993.01820240031004.
- Fishery and Aquaculture Statistics: SECTION 2 – Food balance sheets and fish contribution to protein supply, by country from 1961 to 2007. Rome: Food and Agriculture Organization of the United Nations (2008)
- Cott, J.; Hibbeln, J. R. (2001). "Lack of seasonal mood change in Icelanders". The American Journal of Psychiatry. 158 (2): 328. PMID 11156835. doi:10.1176/appi.ajp.158.2.328.
- SAD Treatment | SAD Lamp | SAD Light | SAD Cure | Seasonal Affected Disorder Britebox Energise Case Study. Britebox.co.uk. Retrieved on March 24, 2013.
- One in five suffers from SAD. BreakingNews.ie (November 10, 2007). Retrieved on March 24, 2013.
- van der Sman (October 28, 2004) Donkere dagen: Winterdepressie verklaard. Elsevier.nl. Retrieved on March 24, 2013.
- Rosenthal, Norman E. (2006). Winter Blues: Everything You Need to Know to Beat Seasonal Affective Disorder (Revised ed.). New York: The Guilford Press. ISBN 978-1593852146.
- More, Lee Kremis (December 26, 1994). "It's Wintertime: When Winter Falls, Many Find Themselves In Need Of Light". Milwaukee Sentinel. Gannett News Service.
- Ban, Thomas A. (2011). Gershon, Samuel, ed. An Oral History of Neuropsychopharmacology, The First Fifty Years, Peer Interviews. 5. American College of Neuropsychopharmacology.
- Lozano, G. A. (2015). "SAD effects on grantsmanship". BioEssays. 37 (1): 10–11. doi:10.1002/bies.201400165.