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===Psychology===
===Psychology===
Psychological disorders can be affected by seasonal changes and result in suicide. There is also a “physiological strain that results from the low ambient temperatures”, where suicidal ideations are considered to stem from <ref>[Van de Wolfshaar, K. E.; De Roos, A. M.; Persson, L. (2008). Population feedback after successful invasion leads to ecological suicide in seasonal environments. Ecology, 89, 259-268.]</ref>. A similar psychology-based experiment, directed by Friedrich V. Wenz, measured seasonal effects on suicide rates. He applied further research to the association between seasonal effects and psychopathology. Wenz “investigated the relation of 2 components of loneliness, present and future loneliness, to seasonality of suicide attempts” <ref> [Wenz, F. V. (1977). Seasonal Suicide Attempts and Forms of Loneliness. Psychological Reports, 40, 807-810.]</ref> . Wenz’s empirical literature states that that suicide attempts from feelings of loneliness were highest in spring and summer and lowest in winter <ref> [Wenz, F. V. (1977). Seasonal Suicide Attempts and Forms of Loneliness. Psychological Reports, 40, 807-810.]</ref>. On the other hand, “The mean scale scores for present and future loneliness were greatest for spring and winter, the peak seasons for the timing of suicide attempts…persons may actually postpone acts of attempted suicide in order to participate and become emotionally involved in important annual ceremonies” . <ref> [Wenz, F. V. (1977). Seasonal Suicide Attempts and Forms of Loneliness. Psychological Reports, 40, 807-810.]</ref>
Psychological disorders can be affected by seasonal changes and result in suicide. There is also a “physiological strain that results from the low ambient temperatures”, where suicidal ideations are considered to stem from <ref>[Van de Wolfshaar, K. E.; De Roos, A. M.; Persson, L. (2008). Population feedback after successful invasion leads to ecological suicide in seasonal environments. Ecology, 89, 259-268.]</ref>. A similar psychology-based experiment, directed by Friedrich V. Wenz, measured seasonal effects on suicide rates. He applied further research to the association between seasonal effects and psychopathology. Wenz “investigated the relation of 2 components of loneliness, present and future loneliness, to seasonality of suicide attempts” <ref name=Wenz> [Wenz, F. V. (1977). Seasonal Suicide Attempts and Forms of Loneliness. Psychological Reports, 40, 807-810.]</ref> . Wenz’s empirical literature states that that suicide attempts from feelings of loneliness were highest in spring and summer and lowest in winter <ref name=Wenz/>. On the other hand, “The mean scale scores for present and future loneliness were greatest for spring and winter, the peak seasons for the timing of suicide attempts…persons may actually postpone acts of attempted suicide in order to participate and become emotionally involved in important annual ceremonies” . <ref name=Wenz/>


The [[Diagnostic and Statistical Manual of Mental Disorders]], 4th ed., (DSM-IV) categorizes [[seasonal affective disorder]] as a specifier of major depression.<ref>[American Psychiatric Association. Task Force on DSM-IV. Diagnostic and Statistical Manual of Mental Disorders. 4th ed. Washington, D.C.: American Psychiatric Association, 1994.]</ref> According to [[Webmd]], SAD is certain type of [[depression]] that typically affects individuals on a negative spectrum due to the lack of sunlight. Other factors that give light to this disorder include: impaired sleep-wake schedule, disrupted [[circadian rhythm]]s, and the decrease in a [[neurotransmitter]] called [[serotonin]]. If a parent or related guardian has suffered from [[SAD]], there is not a likelihood of the offspring/blood-related individual to be susceptible as well <ref>[Allen, J. M.; Lam, R. W.; Remick, R. A.; et al. (1993). Depressive Symptoms and Family History in Seasonal and Non-seasonal Mood Disorders. American Journal of Psychiatry, 150, 443-448.]</ref>. Symptoms of SAD include loss in energy, decrease in overall appetite, social withdrawal, and unhappiness/irritability. In severe enough cases, these symptoms have been known to gradually lead to suicidal attempts, ideations, and/or plans when battling with seasonal affective disorder. <ref>[http://depression.about.com/cs/sad/a/sad.htm]</ref> These symptoms can be idealized as warning signs of suicide.
The [[Diagnostic and Statistical Manual of Mental Disorders]], 4th ed., (DSM-IV) categorizes [[seasonal affective disorder]] as a specifier of major depression.<ref>[American Psychiatric Association. Task Force on DSM-IV. Diagnostic and Statistical Manual of Mental Disorders. 4th ed. Washington, D.C.: American Psychiatric Association, 1994.]</ref> According to [[Webmd]], SAD is certain type of [[depression]] that typically affects individuals on a negative spectrum due to the lack of sunlight. Other factors that give light to this disorder include: impaired sleep-wake schedule, disrupted [[circadian rhythm]]s, and the decrease in a [[neurotransmitter]] called [[serotonin]]. If a parent or related guardian has suffered from [[SAD]], there is not a likelihood of the offspring/blood-related individual to be susceptible as well <ref>[Allen, J. M.; Lam, R. W.; Remick, R. A.; et al. (1993). Depressive Symptoms and Family History in Seasonal and Non-seasonal Mood Disorders. American Journal of Psychiatry, 150, 443-448.]</ref>. Symptoms of SAD include loss in energy, decrease in overall appetite, social withdrawal, and unhappiness/irritability. In severe enough cases, these symptoms have been known to gradually lead to suicidal attempts, ideations, and/or plans when battling with seasonal affective disorder. <ref>[http://depression.about.com/cs/sad/a/sad.htm]</ref> These symptoms can be idealized as warning signs of suicide.

Revision as of 00:09, 19 April 2012

Research on seasonal effects on suicide rates suggests that the prevalence of suicide is actually greatest during late spring and early summer months,[1] despite the common belief that suicide rates peak during the cold and dark months of the winter season.[2]

General effects

The Center for Disease Control and Prevention and the National Center for Health Statistics report that suicide rates in the United States are lowest during the winter months and highest in the summer and springtime. F. Stephen Bridges’s article “Seasonal Changes in Suicide in the United States, 1971 to 2000”, asserts that there is "A high incidence in early spring (April and May) and…also a low incidence in winter" of suicides [3]. Bridge's study focused on suicide risk by examining the monthly distribution of suicides from the 1970s, 80s, and 90s, via a "harmonic time series model" [4] with six observable harmonic cycles within the given year. The results show a consistent pattern of suicide risk with most suicides occurring in the spring/summer and the fewest during the winter months. Specifically, Bridge found that in the 1970's "about 47% of the total variances can be explained by the seasonal components" [5] within that given decade (with more suicides in spring/summer). The period from 1980-1990 in the study showed, "The seasonal component of suicide incidence for the time period 1981 through 1990 is clearly significant and records about a 27.7% increase in seasonal contribution by comparison with the previous period". [6] For the 1990-2000 time period, the study reports that "the significant seasonal rhythm were explained in 63% of the total variation." [7].

According to F. Stephen Bridges,[7] recent research from industrialized countries (including Finland, Sweden, Australia and New Zealand, England, and Wales) has provided enough information to show a decrease in seasonal effects on suicide rates over the past few decades. Within the country of Greece, research studies indicate that the seasonal variations of mortality from suicide are “more frequent during the spring and summer months…but no regular annual rhythm”. [8]. The researchers proposed "the seasonal variation of suicide follows more closely the seasonal variation of sunshine rather than the corresponding variation of temperature". [9] Studies of Brazil in the Southern Hemisphere have shown that "the peak number of suicides occurred in spring (November) in men and women of Rio Grande do Sul state and in men of Parana and Santa Catarina states, and in early summer (January) for women of Parana' state." [10] Few scientific assessment studies have focused on seasonal suicide variations within the southern hemisphere.

Eleni Petridou, a professor of Preventive Medicine & Epidemiology and former member in Preventive Medicine F-1000, conducted a collaborative international study related to seasonal effects on suicide rates that involved twenty different countries. The results showed an early summer peak in suicides. She later concludes that “seasonal variation in suicide incidence could be explained by the increase in sunshine in summer months because of a relationship between sunshine, high temperatures and suicide rate.” [11]. Australian researchers, J. Edwards and F. Whitlock, doing similar work, found a “spring peak in the number of suicides committed in Brisbane, Australia, but the results were not statistically significant…and, also, that Dublin reported that the incidence of suicide varied according to seasons in the northern hemisphere.” [12].

Explanations

French sociologist Émile Durkheim found a similar pattern of results. Durkheim reported that most suicides occurred in the spring, but not summer. Durkheim believed that a sociological understanding, rather than the role of nature, was responsible for the high suicide rates he found. Durkheim declared that most suicides took place in the spring because "everything begins to awake; activity is resumed, relations spring up, interchanges increase. In other words, it is the density of human interactions, and not the environment that caused higher incidence of suicide in spring or summer." [13]. Other researchers who have found an association between seasonal effects and suicide rates have also concluded that suicides tend to peak during the spring or summer. [14][11]

Many people believe that suicide rates peak during the winter months. [15] Intuitively, this makes sense not only because seasonal affective disorder, but also because all of the studies on depression examined during the winter months. [16] Harsher weathers increased the prevalence of diseases such as pneumonia hypothermia, which have mainly been from the minimal amount of sunlight in the winter time. [17]. Some also believe that “holiday cheer amplifies loneliness and hopelessness in people who have lost loved ones, or who have high expectations of renewed happiness during the holiday season, only to be disappointed.” [18].

Since the act of suicide is primarily considered as a deliberate conscientious motive, one’s behaviors, ideations, or attempts can be both exogenous (within the boundaries of social and economic elements) and endogenous (demographical, pathological, clinical, seasonal). According to Serbian researcher Časlav Milić, “most studies show that suicide…is in direct connection with seasons. Annual trend shows the peak from March to May (from early to late spring) for violent suicide”. [19]

Gender

The effect of seasonal changes on suicide rates affects both genders on different scales. As noted in the research report of the “Analysis of the Seasonal Pattern in Suicide” by Timo Partonen and colleagues, “There was a seasonal effect on suicide occurrence among the study population [in Finland], and the risk of suicide was highest in May and lowest in February over the study period”…males with an incidence of 42.56 (N=21,622) and females with an incidence of 10.86 (N=5847).[20]. Their findings demonstrate that both male and females suicidal rates tend to be higher during the spring and summer months (combined gender inference of: April ~ 27.24; May ~ 30.04; June ~ 28.86; July ~ 27.83) compared to winter (Nov. ~ 25.77; Dec. ~ 23.17; Jan. ~ 24.07; Feb. ~ 23.16). Similar results were reported in Lester and Franks’ article “Sex differences in the seasonal distribution of suicides”. These researchers focused on the influence of climate and social integration, in regards to suicide rates categorized by gender. Their data suggest that both male and female genders showed a “bimodal distribution of suicides and the sexes, but did not differ significantly from each other (x@=l2.29, d.f.=ll, P>0.30)” [21]. The authors hypothesized that the high summer peaks in suicide deaths exhibit a hope amongst the emotionally discomforted that winter might bring an end to the “social isolation and depression brought about by the cold weather”[22]. In contrast to these findings, some studies indicate that males have only one peak of suicide during the spring and early summer while women show two peaks of suicide throughout the year, which is during the spring and fall: “The seasonal distribution of suicides among the 117 males was similar and showed a significant seasonality: spring and summer peaks (33 and 29%, respectively) and fall–winter lows (18% and 20%, respectively, χ2=7.684, d.f.=3, P=0.053)” [23], [24], [25], [26].

Biology

Biological explanations of seasonal effects on suicide rates tend to focus on seasonal variation in hormone changes and neurotransmitter levels (most notable neurotransmitters include dopamine, norepinephrine, serotonin, and acetylcholine). Chronobiological research conducted by a team clinical scientists in Belgium [27] has revealed that many “biochemical, metabolic and immune functions, which may be related to suicide, suicidal behavior or ideation or major depression, are organized along a multifrequency seasonal time-structure” [28]. Within the same field of research, evidence was found by calculating “serum total cholesterol concentrations to show a clear seasonality with lower levels in midyear than in winter [29], and neuropeptides in normal controls: findings with while lower serum cholesterol levels may be related to a higher occurrence of suicide [30]. These findings clearly state that there is a relationship between summer suicidal rates and biochemical (eg, plasma L-TRP and melatonin levels, [3H]paroxetine binding to blood platelets), metabolic (serum total cho- lesterol, calcium and magnesium concentrations) and immune (number of peripheral blood lymphocytes and serum sIL-2R) variables. [31]

Another study produced by a Belgium team of scientists focused on the association between depression, suicide, and the amount of PUFA (poly-unsaturated fatty acids). Their background knowledge states “depression is accompanied by a depletion of n-3 poly-unsaturated fatty acids (PUFAs)” [32]. Their methodology was taking periodic blood samples—every month throughout one full year—of healthy volunteers successfully allowed them to analyze the “PUFA composition in serum phospholipids and related those data to the annual variation in the mean weekly number of suicides”. This group of researchers used a statistical computing device called ANOVA to document their results. By utilizing the ANOVA table, the researchers found that PUFA acids like arachidonic acid, eicosapentaenoic acid, and docosahexaenoic acid all had significantly lower rates in the winter as opposed to summer months. Consequently, the association between depression, suicide, and PUFA rates is indicative of suicides having biological notion to occur more in the summer than in the winter [33].

Environment

Numerous meteorological variables, such as the amount of sunlight, natural disaster related experiences, and the inability to protect and properly shelter ones home or self, can result in suicidal ideations or attempts. For example, parasuicide, which is the strongest known indicator for a future successful suicide attempt, has been known to have a strong association with weather patterns throughout a given annual season. As noted by Barker et al. in their 1994 article on seasonal and weather factors in parasuicide, “A major finding of this study was…the greatest mean daily number of parasuicide episodes in late spring/early summer and a trough in December/January”.[34] Within their approach, they also exercised a linear model to accurately separate any “seasonal effects and seasonally-related weather effects”. [34] Women and men have yielded different climate factors for both genders. The women’s data concluded that the meteorological factors that accounted for large parasuicidal effects were, in specificity, maximum temperature, rainfall, and cloud cover. On the other hand, rain, cloud cover, poor visibility, and windy days were the important associations found between daily parasuicide frequencies in men. Additionally, “environmental temperature, wind and humidity together affect the rate of body cooling, with hot, humid, still days decreasing evaporative cooling”. [34] These scientific findings state that elevated levels in environmental heat have been known to “produce thermal stress causing physiological, psychological and behavioral change, which may predispose a person to parasuicidal behavior, or precipitate parasuicide in someone already considering it.”[34]

Petridou and colleagues, along with the Organization for Economic Co-operation and Development (OECD), were able to show a “consistency of an early summer excess incidence of suicide around the world, and the further association of suicide with hours of sunshine, strongly suggest that a physical environmental factor plays an important role in the triggering of suicide” across twenty different OECD countries around the world. [11] All but two (Australia and New Zealand) of the countries on their list showed peaks in suicide rates between the months of April and June. Petridou and researchers selectively grouped the countries ‘within-country seasonality’ and found that “of the 20 OECD countries in the study, 18 are in the northern hemisphere and two are in the southern hemisphere (Australia and New Zealand showed peaks in November or December)”. Along with Petridou’s previous literature, she says, “it is possible that the excess suicide risk during the summer months could be associated with behavioral changes of the persons not attributed directly to sunshine…so that suicide risk could be affected by factors associated with more free time rather than more sunshine”. In appeal to Australia’s exclusive seasonal rates of suicide, studies have confirmed the country's suicidal peak in December and January is also from the number of “bright sunlight hours” [35]

Psychology

Psychological disorders can be affected by seasonal changes and result in suicide. There is also a “physiological strain that results from the low ambient temperatures”, where suicidal ideations are considered to stem from [36]. A similar psychology-based experiment, directed by Friedrich V. Wenz, measured seasonal effects on suicide rates. He applied further research to the association between seasonal effects and psychopathology. Wenz “investigated the relation of 2 components of loneliness, present and future loneliness, to seasonality of suicide attempts” [37] . Wenz’s empirical literature states that that suicide attempts from feelings of loneliness were highest in spring and summer and lowest in winter [37]. On the other hand, “The mean scale scores for present and future loneliness were greatest for spring and winter, the peak seasons for the timing of suicide attempts…persons may actually postpone acts of attempted suicide in order to participate and become emotionally involved in important annual ceremonies” . [37]

The Diagnostic and Statistical Manual of Mental Disorders, 4th ed., (DSM-IV) categorizes seasonal affective disorder as a specifier of major depression.[38] According to Webmd, SAD is certain type of depression that typically affects individuals on a negative spectrum due to the lack of sunlight. Other factors that give light to this disorder include: impaired sleep-wake schedule, disrupted circadian rhythms, and the decrease in a neurotransmitter called serotonin. If a parent or related guardian has suffered from SAD, there is not a likelihood of the offspring/blood-related individual to be susceptible as well [39]. Symptoms of SAD include loss in energy, decrease in overall appetite, social withdrawal, and unhappiness/irritability. In severe enough cases, these symptoms have been known to gradually lead to suicidal attempts, ideations, and/or plans when battling with seasonal affective disorder. [40] These symptoms can be idealized as warning signs of suicide.

Pendse, Westrin, and Engstrom’s research study on temperament traits on seasonal affective disorder and suicidal attempters determined that “the suicidal behavior of SAD patients is not a prominent problem, even though SAD patients often present suicidal ideation.” [41] Pendse and colleagues compared a small sample of patients (population sample of eighty-seven) who suffered from seasonal affective disorder and also hospitalized suicide attempters (population sample of sixty-five) who had undergone “non-seasonal major depression” by using the Comprehensive Psychopathological Rating Scale (CPRS). [41]. Results state that the SAD controlled group had a significant probability (p-value of < .05) of scoring higher on non-psychotic tests than the non-SAD suicidal attempters—when both experimental control groups being analyzed for items such as “hostile feelings, indecision (negatively), lassitude, failing memory, increased sleep, muscular tension, loss of sensation or movement, and disrupted thoughts, and the observed items were perplexity, slowness of movement (negatively), and agitation.” [41].

Treatments on light therapy have been proven as effective in suicidal patients suffering from the SAD effect and winter depression. [42]

References

  1. ^ Clauss-Ehlers, Caroline. (2010). Encyclopedia of Cross-Cultural School Psychology, Volume 2, 961
  2. ^ [Press release] Romer, Dan. (2001). Media Continue to Perpetuate Myth of Winter Holiday – Suicide Link. The Annenberg Public Policy Center.
  3. ^ Bridges, F. S.; Yip, P. S. F.; Yang, K. C. T. (2005). Seasonal changes in suicide in the United States, 1971 to 2000. Perceptual and Motor Skills, 100, 920-924.
  4. ^ Bridges, F. S.; Yip, P. S. F.; Yang, K. C. T. (2005). Seasonal changes in suicide in the United States, 1971 to 2000. Perceptual and Motor Skills, 100, 920-924.
  5. ^ Bridges, F. S.; Yip, P. S. F.; Yang, K. C. T. (2005). Seasonal changes in suicide in the United States, 1971 to 2000. Perceptual and Motor Skills, 100, 920-924.
  6. ^ Bridges, F. S.; Yip, P. S. F.; Yang, K. C. T. (2005). Seasonal changes in suicide in the United States, 1971 to 2000. Perceptual and Motor Skills, 100, 920-924.
  7. ^ a b Bridges, F. S.; Yip, P. S. F.; Yang, K. C. T. (2005). Seasonal changes in suicide in the United States, 1971 to 2000. Perceptual and Motor Skills, 100, 920-924.
  8. ^ Bridges, F. S.; Yip, P. S. F.; Yang, K. C. T. (2005). Seasonal changes in suicide in the United States, 1971 to 2000. Perceptual and Motor Skills, 100, 920-924.
  9. ^ Bazas, T.; Jemos, J.; Stefanis, K.; et al. (1979). Incidence and Seasonal-Variation of Suicide Mortality in Greece. Comprehensive Psychiatry, 20, 15-20.
  10. ^ Benedito-Silva, Ana Amelia; Pires, Maria Laura Nogueira; Calil, Helena Maria. (2007). Seasonal variation of suicide in Brazil. Chronobiology International, 24, 727-737.
  11. ^ a b c Petridou E, Papadopoulos FC, Frangakis CE, Skalkidou A, Trichopoulos D. (2002). A role of sunshine in the triggering of suicide. Epidemiology 13, 106–109
  12. ^ Edwards, J.E., Whitlock, F.E. (1968). Suicide and attempted suicide in Brisbane. Med J Psychiatry, 1, 932–938.
  13. ^ [Kposowa, Augustine J., D’Auria, Stephanie. (2010) Association of temporal factors and suicides in the United States, 2000–2004. Social Psychiatry Epidemiology, 45, 433-445.]
  14. ^ [Kalediene R, Starkuviene S, Petrauskiene J. (2006). Seasonal patterns of suicides over the period of socio-economic transition in Lithuania. BMC Pub Health, 6, 40.]
  15. ^ Clauss-Ehlers, Caroline. (2010). Encyclopedia of Cross-Cultural School Psychology, Volume 2, 961
  16. ^ [1]
  17. ^ [Deisenhammer, E. A. (2003). Weather and suicide: the present state of knowledge on the association of meteorological factors with suicidal behaviour. Acta Psychiatrica Scandinavica, 108, 402-409.]
  18. ^ Jacquelyn Rudis, True or False: Depression and Suicide Rates Rise During the Holiday Season, Beth Israel Deaconess Medical Center, accessed April 12, 2012
  19. ^ [Milic, Caslav. (2010). Seasonal variations--risk factor of committing suicide. Medicinski pregled, 63, 531-534.]
  20. ^ [Partonen, T.; Haukka, J.; Nevanlinna, H.; et al. (2004). Analysis of the seasonal pattern in suicide. Journal of Affective Disorders, 81, 133-139.]
  21. ^ [Lester, D., Frank, M. Sex differences in the seasonal distribution of suicides. (1988). The British Journal of Psychiatry. 153, 115-117]
  22. ^ [Lester, D., Frank, M. Sex differences in the seasonal distribution of suicides. (1988). The British Journal of Psychiatry. 153, 115-117]
  23. ^ [Eastwood, M. R.; Peacocke, J. (1976). Seasonal Patterns of Suicide, Depression, and Electroconvulsive-Therapy. British Journal of Psychiatry, 129, 472-475.]
  24. ^ [Meares, R.; Mendelsohn, F. A. O.; Milgromfriedman, J. (1981). A Sex Difference in the Seasonal Variation of Suicide Rate – A Single Cycle For Men, 2 Cycles for Women. British Journal of Psychiatry, 138, 321-325.]
  25. ^ [Micciolo, R.; Williams, P.; Zimmermanntansella, C.; et al. (1991). Geographical and Urban Rural Variation in the Seasonality of Suicide – Some Further Evidence. Journal of Affective Disorders, 21, 39-43.]
  26. ^ [Rihmer, Z.; Rutz, W.; Pihlgren, H.; et al. (1998). Decreasing tendency of seasonality in suicide may indicate lowering rate of depressive suicides in the population. Psychiatry Research, 81, 233-240.]
  27. ^ [Maes, M.; Scharpe, S.; Dhondt, P.; et al. (1996). Biochemical, metabolic and immune correlates of seasonal variation in violent suicide: A chronoepidemiologic study. European Psychiatry, 11, 21-33.]
  28. ^ [Touitou Y, Haul E. Biologic rhythms from biblical to modem times: a preface. (1992). Biologic Rhythms in Clinical and Laboratory Medicine. 1-6.]
  29. ^ [Gordon DJ, Trost DC, Hyde J, Whalley F, Jacobs DR. (1981). Seasonal cholesterol cycles: the lipids research clinic coronary primary prevention trial placebo group. Circulation, 76, 1224-31]
  30. ^ [Muldoon MF. Manuck SB, Mathews KM. (1990). Lowering cholesterol concentrations and mortality: a quantitative review of primary prevention trials. British Medical Journal, 301, 309-14]
  31. ^ [Maes, M.; Scharpe, S.; Dhondt, P.; et al. (1996). Biochemical, metabolic and immune correlates of seasonal variation in violent suicide: A chronoepidemiologic study. European Psychiatry, 11, 21-33.]
  32. ^ [De Vriese, S. R.; Christophe, A. B.; Maes, M. In humans, the seasonal variation in poly-unsaturated fatty acids is related to the seasonal variation in violent suicide and serotonergic markers of violent suicide. (2004). Prostaglandins Leukotrienes and Essential Fatty Acids, 71, 13-18.]
  33. ^ [De Vriese, S. R.; Christophe, A. B.; Maes, M. In humans, the seasonal variation in poly-unsaturated fatty acids is related to the seasonal variation in violent suicide and serotonergic markers of violent suicide. (2004). Prostaglandins Leukotrienes and Essential Fatty Acids, 71, 13-18.]
  34. ^ a b c d Barker, A.; Hawton, K.; Fagg, J.; Jennison, C. (1994). Seasonal and Weather Factors in Parasuicide. British Journal of Psychiatry, 165, 375-380.
  35. ^ Lambert, G.; Reid, C.; Kaye, D.; et al. (2003). Increased suicide rate in the middle-aged and its association with hours of sunlight. American Journal of Psychiatry, 160, 793-795.
  36. ^ [Van de Wolfshaar, K. E.; De Roos, A. M.; Persson, L. (2008). Population feedback after successful invasion leads to ecological suicide in seasonal environments. Ecology, 89, 259-268.]
  37. ^ a b c [Wenz, F. V. (1977). Seasonal Suicide Attempts and Forms of Loneliness. Psychological Reports, 40, 807-810.]
  38. ^ [American Psychiatric Association. Task Force on DSM-IV. Diagnostic and Statistical Manual of Mental Disorders. 4th ed. Washington, D.C.: American Psychiatric Association, 1994.]
  39. ^ [Allen, J. M.; Lam, R. W.; Remick, R. A.; et al. (1993). Depressive Symptoms and Family History in Seasonal and Non-seasonal Mood Disorders. American Journal of Psychiatry, 150, 443-448.]
  40. ^ [2]
  41. ^ a b c [Pendse, B.; Westrin, A.; Engstrom, G. (1999). Temperament traits in seasonal affective disorder, suicide attempters with non-seasonal major depression and healthy controls. Journal of Affective Disorders Volume, 54, 55-65.]
  42. ^ [Lam, RW (Lam, RW); Tam, EM (Tam, EM); Shiah, IS (Shiah, IS); Yatham, LN (Yatham, LN); Zis, AP (Zis, AP). (2000). Effects of light therapy on suicidal ideation in patients with winter depression. Journal of Clinical Psychiatry, 61, 30-32.]
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