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Why Does Increased Sun Exposure Seem to Increase Rates of Suicide?

Samantha Webb

October 5, 2009



Extensive research by epidemiology and psychiatry professionals has indicated a direct relationship between sun exposure and suicide.  The in-depth research on this relationship has revealed that suicide risk peaks in the late spring and troughs in late autumn (Lambert et al. 2003, Preti, 1997).  Researchers have performed studies in countries around the world including Brazil and Italy that have verified this seasonal suicide risk and no doubt can remain of the validity of this relationship.  Evidence explored in an article discussing the seasonality in suicides presents data clearly stating that only violent suicides differ by seasons.  According to this article, non-violent suicides do not follow seasonal trends (Preti and Miotto, 1998).



Although these studies have confirmed that the relationship between suicide and sun exposure exists, the cause has yet to be determined.  Researchers have considered a number of plausible reasons for the correlation between suicide rates and sunlight exposure.  The simplest of these hypotheses suggests that sunlight acts as an antidepressant and is often used in treatment therapies for depression.  Therefore, when a patient has suffered from low sunlight exposure for a long period of time, the reintroduction of sunlight into their lives induces motivation.  Sunlight’s ability to improve a person’s mood occurs after this motivation.  Since the motivation transpires before the mood elevation, the sunlight would actually induce a short-term increased suicide risk (Papadopoulos et al., 2005).   

Another hypothesis suggested by researchers revolves around the circadian rhythms that take place during sleep.  Researchers suggest that abnormal circadian rhythms commonly found in depressed individuals may occur because of a lack of synchronization between environmental cues and internal clocks.  Environmental cues such as daylight and temperature help to set our “internal clocks” or circadian rhythms.  These environmental cues fluctuate throughout the year.  Daylight hours wax and wane the farther away from the Equator while temperatures change according to the season.  As these environmental factors vary throughout the year, the circadian rhythms can become abnormal which, in turn, can decrease the amount of sleep, increase depressive symptoms and heighten the risk of suicide (Souetre et al, 1987)

The final hypothesis suggested by researchers involves sunshine-dependent hormones such as melatonin, cortisol, serotonin, and L-tryptophan (Petridou et al., 2002).  According to this hypothesis, during months of few hours of daylight, these hormones would be suppressed.  As soon as hours of daylight hours increase, hormone levels would suddenly rise and the drastic change in mood would induce a risk of suicide.  Although melatonin is linked to mood stabilization, this hypothesis has yet to be proved.



The research done on sunlight-related suicide focused solely on proving the correlation between increased sunlight and the rise of suicides.  Research on melatonin has suggested that increased intake during times of extended sun exposure might reduce mood abnormalities.  Since sunlight naturally debilitates melatonin’s ability to decrease mood abnormalities, increased intake may be effective.  However, until further research discovers the biological effect of the sunlight on a person’s mental health, no treatment can be advised.  Based on the current findings, heightened suicide prevention measures should be in place during the late spring and early summer months for those patients whose depression or other mental health conditions is affected greatly by sun exposure. 


The Researchers:

Those interested in the relationship between sun exposure and suicide risk have been professionals involved in psychiatry and epidemiology.  Since suicide often results from severe depression and depression often occurs due to a lack of sunlight, psychiatrists would naturally try to find the link between sun exposure and suicide risk in order to understand and treat their patients more effectively.  Similarly, epidemiologists try to identify the causes of diseases and the cause of suicide is often complex.  If epidemiologists identify the various risks of suicide, they can understand the cause in a more accurate manner. 


The Research:

My research extended to scholarly journals.  The articles were written by psychiatric, epidemiological, and psychological professionals.  I chose to research scholarly journals because the articles have been reviewed no unproven claims have been made.  Although all of my sources provided useful information, four particular studies proved immeasurably valuable.  To begin my research, I searched sun exposure and suicide and then used abstracts from PubMed to guide me to relevant articles.  From these abstracts, I found the full articles on GoogleScholar or through the Vanderbilt Library article and e-journal locator. 


Past Experiments:

Although numerous experiments have reported a peak in suicide during the late spring and early summer months, the link between seasons and suicide has yet to be discovered.  Research and personal accounts have suggested that moods tend to deteriorate as the number of daily hours of sunlight decreases.  Therefore, one would expect rates of suicide to peak during the late fall, early winter months.  “A Role of Sunshine in the Trigger of Suicide” seeks to evaluate this counter-intuitive relationship.  The researchers of this study first calculated the total hours of sunlight per month from twenty countries.  The researchers then utilized a procedure to estimate the peak suicide months and the relative risk of committing suicide for each month.  Of the twenty countries studied during this experiment, eighteen were in the Northern Hemisphere and two were in the Southern Hemisphere.  However, all countries, regardless of Hemisphere, experienced a seasonality of suicide rates.   In particular, the peaks of suicide for every country occurred during the late spring, early summer months of the year.  A positive correlation occurred between the number of daylight hours and the suicide risk.  A rise in suicide during summer months could have been attributed to behavioural differences, such as more free time.  However, the researchers eliminated the summer months to measure the seasonality of the remaining nine months and still found a seasonal change.  Therefore, behavioural differences can be eliminated from the argument.  Although the researchers could never determine the direct cause of sunlight-related suicide, suggestions of the effects of melatonin and the lag time between exposure and outcome were explained briefly. The study even went so far as to suggest that increased intake of melatonin during seasons of frequent sun exposure might be able to regulate moods more effectively (Petridou et al, 2002)

“The Seasonality of Suicide in Sweden” studied the relationship between the seasonality tendencies of suicide and the psychiatric morbidity of those who commit suicide.  The method of study used data from suicide victims in Sweden between 1992 and 2003.  This data contained psychiatric information about the victims up to five years before their suicide.  Researchers defined seasonality suicide as the relative risk of suicide during the peak months of suicides compared to the risk of suicide during the lowest months of suicides.  The same experiment found that both male and female suicide rose during late spring and early summer.  These suicides were particularly pronounced in victims with a psychiatric disease compared to those without psychiatric history.  However, results varied when comparing mental health disorders resulting in suicide for men and women.  Male suicides were often preceded by a history of depression whereas female suicides were accompanied by past neurotic, stress-related, or somatoform disorders (Reutfors et al., 2009). 

Many researchers have studied the effects of sun exposure and the seasonality of suicides in the Northern Hemisphere.  Although not as many studies have occurred in the Southern Hemisphere, similar findings have been discovered.  The peak months of suicide in both hemispheres occur during months with more hours of sunlight per day.  This observation has led researchers to wonder whether the increase in suicide is related to sunshine-dependent hormones such as melatonin.  Researchers decided to study the role of these hormones in the triggering of suicide by hypothesizing that, if these hormones were, in fact, the trigger, then greater variation in suicides would occur  the farther away from the Equator.  “Sunshine and suicide at the tropic of Capricorn, Sao Paulo, Brazil, 1996-2004” studies the seasonal variation of suicides at Sao Paulo, Brazil.  Researchers gathered information regarding suicides, solar irradiance, and temperature during eight years.  In order to obtain this data, two meteorological stations in the north and south areas of the city picked up information daily to be compared to suicide rates. Seasonal suicide rates did not change drastically throughout the seasons.  In conclusion, suicide rates seem to be affected only in regions with more dramatic changes in daylight hours.  The association between sunlight and suicide becomes weaker the closer the region is to the Equator.  Although severely depressed men have experienced melantonin abnormalities, other studies reveal that the relationship between melatonin, depression, and seasons has not been clearly defined enough to consider it the link between sun exposure and suicide (Nejar, Bensenor, and Lutofo 2004).

A study in Australia sought to determine an association between environmental factors and the rate of suicides.  “Increased Suicide Rate in the Middle-Aged and Its Association with Hours of Sunlight” studied the frequency of suicide and the meteorological effects occurring during suicides between 1990 and 1999 in Victoria, Australia.  Data on suicide included age and gender gathered from the Victoria State Coroner’s Office and the Victorian Institute of Forensic Medicine.  Meteorological data determined by the Australian Commonwealth Bureau of Meteorology included information regarding temperature, hours of sunlight, rainfall, and atmospheric pressure.  The results of this study confirmed that suicide rates rose in the late spring, early summer and troughed in the late autumn and early winter.  While violent suicide followed these trends, non-violent suicides did not.  The results clearly show that daylight hours affect the rate of suicide and, while it may be easy to turn to environmental factors, social factors must also be considered. 

The relationship between sunlight exposure and suicide is one that should be researched continually until a clear cause emerges.  Unfortunately, although researchers are aware of the relationship, no proven treatment can be prescribed until the cause is determined.  Until that time, awareness of the problem will have to be sufficient and general suicide watch methods for those prone to suicide can be put into place during the peak months. 








Lambert, G. et al. (2003).  Increased Suicide Rate in the Middle-Aged and Its Association with Hours of Sunlight.  American Journal of Psychiatry, (160), 793-795.


Nejar, K.A., Bensenor, I.M., Lutofo, P.A. (2007).  Sunshine and suicide at the tropic of Capricorn, Sao Paulo, Brazil, 1996-2004.  Rev Saude Publica, 41(6), 1062-4.


Papadopoulos, F.C. et al. (2005). Exploring Lag and Duration Effect of Sunshine in Triggering Suicide.  Journal of Affective Disorders, 88(3), 287-297.


Petridou, E. et al.(2002).  A role of sunshine in the triggering of suicide.  Epidemiology, 13(1), 106-9.


Preti, A. (1997).  The influence of seasonal change on suicidal behaviour in Italy.  Journal of Affective Disorders, 44(2-3), 123-30.


Preti, A. and Miotto, P. (1998).  Seasonality in suicides: the influence of suicide method, gender and age on suicide distribution.  Psychiatry Research, 81(2), 219-231.


Reutfors, J. et al. (2009).  Seasonality of suicide in Sweden: Relationship with psychiatric disorder.  Journal of Affective Disorders.


Souetre, E. et al. (1987).  Seasonality of suicides: environmental, sociological and biological covariations.  Journal of Affective Disorders, 13(3), 215-25.


NOTE:  the image used in this document was taken from Microsoft Office Clip Art.




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