Effects of sunshine on suicide rates

doi:10.1016/j.comppsych.2011.06.003

Comprehensive Psychiatry

Volume 53, Issue 5, July 2012, Pages 535-539

https://doi.org/10.1016/j.comppsych.2011.06.003 Get rights and content

Abstract

Objectives

Seasonal spring peaks of suicide are well described in epidemiological studies, but their origin is poorly understood. More recent evidence suggests that this peak may be associated with the increase in the duration of sunshine in spring. We investigated the effect of number of sunshine hours per month on suicide rates in Austria between 1996 and 2006.

Methods

Suicide data, differentiated by month of suicide, sex, and method of suicide (violent vs nonviolent methods), were provided by Statistics Austria. Data on the average number of sunshine hours per month were calculated from 39 representative meteorological stations (provided by the Austrian Central Institute for Meteorology and Geodynamics). For statistical analysis, analysis of variance tests, Kruskal-Wallis tests, and Pearson correlation tests were used.

Results

A total of 16 673 suicides with a median of 126 ± 19.8 suicides per month occurred in the examined period. A clear seasonal pattern was observed, with suicide frequencies being highest between March and May and lowest between November and January (df = 11, F = 5.2, P < .0001) for men (df = 11, F = 4.9, P < .0001) and women (df = 11, F = 2.4, P = .008). The average number of sunshine hours per month was significantly correlated with the number of suicides among both sexes (r = .43, P < .0001), violent methods (r = .48, P < .0001) but not with nonviolent methods (r = .03, P = .707).

Conclusions

This study shows that seasonal changes in sunshine account for variations in the number of suicides and especially violent suicides. We propose that sunshine, via interactions with serotonin neurotransmission, may trigger increased impulsivity and promote suicidal acts. However, because of the hypothesis-generating design of this study, more research is needed to further clarify the role of sunshine in triggering neurobiologic changes, which might contribute to suicidal behavior.

Introduction

During the past decades, the insight in the pathways and effects of sunlight on human behavior has continuously grown. Sunlight induces neurobiologic changes in the mammalian brain, especially via modulation of serotonin neurotransmission [1]. Positron emission tomography studies in healthy humans using highly selective ligands have shown that an index of serotonin transporter (5-hydroxytryptamine transporter [5-HTT]) density varies throughout the year and is highly correlated with sunlight exposure [2], [3]. Similarly, markers of brain serotonin metabolism were shown to be directly related to bright light exposure [4]. There is also extensive evidence that psychiatric problems or disorders that have been associated with serotonin dysfunction, for example, suicidality and depression, are highly sensitive to seasonal changes, predominantly to sunlight. In addition, it has been shown that the 5-HTT is in a hyperfunctional state during depression in seasonal affective disorders and normalizes after light therapy and in natural summer remission [5].

Several postmortem and genetic studies suggest an involvement of serotonin in suicidal behavior, especially in violent suicides [6], [7], [8], [9], [10], and affective disorders are well recognized to increase the risk of suicide by up to 20-fold [11], [12], [13].

On the other hand, data from several different countries have shown that suicides follow a seasonal pattern, with a maximum peak in spring in Northern latitudes, which is shifted by 6 months in the Southern hemisphere (also occurring in spring) [14], [15], [16], [17]. Although suicide has been proposed to be associated with different environmental measures, which underlie seasonal changes, including temperature, air humidity, air pressure, rainfall, and others, the best neurobiologic model explaining suicide incidence is that of sunlight exposure influencing mood disorders via modulation of serotonin transmission [17], [18], [19], [20], [21], [22]. Furthermore, impulsiveness and aggressive behavior are closely related to suicidal behavior and have been shown to be linked to both serotonergic transmission [23] and seasonal changes [24], [25], [26].

We hypothesized that the suicide incidence in Austria is associated with the average duration of sunshine. Given that aggressive behavior is related to serotonin and seasonal changes in environmental light, we further hypothesized that the association of suicide rates and sunshine will be stronger in individuals using aggressive/violent suicide methods compared with individuals using less violent methods.

Section snippets

Methods

Suicide data for the period 1996 to 2006, differentiated by month of suicide, sex, and method of suicide, were provided by Statistics Austria (classified according to the International Statistical Classification of Diseases, Ninth Edition: E950-E959 and International Statistical Classification of Diseases, Tenth Edition: X60-X84). Suicide methods were further classified by the most common method of distinction as violent (hanging, drowning, shooting, and jumping) or nonviolent methods

Results

A total of 16 673 suicides with a median of 126 ± 19.8 suicides per month occurred in the examined period between 1996 and 2006. A clear seasonal pattern was observed, with suicide frequencies being highest between March and May and lowest between November and January (df = 11, F = 5.2, P < .0001) for men (df = 11, F = 4.9, P < .0001) and women (df = 11, F = 2.4, P = .008). The average number of sunshine hours (153 ± 64.6) was highest from March to August (df = 11, F = 48.5, P < .0001) (see

Discussion

Suicide incidence in Austria followed a clear seasonal pattern over the investigated period of 11 years because suicide frequencies peaked in spring for both sexes. In addition, to our knowledge, our study is the first to show an association between sunshine hours per month and number of suicides in Austria. As expected, violent methods, but not nonviolent methods, were correlated with the number of sunshine hours in the suicide month.

The seasonal spring peak of suicides has been previously

Conclusion

This is the first study from Austria showing that seasonal effects account for variations in the number of suicides and especially violent suicides among both sexes. We showed that the seasonality in suicides is correlated with sunshine and have proposed, based on available evidence, that sunshine, via interactions with serotonin neurotransmission, may trigger increased impulsivity and promote suicidal acts. Findings of this study could help in improving therapeutic strategies aimed at

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Citation Excerpt :
Evidence links multiple seasonal environmental factors with suicide. For example, sunlight exposure has been repeatedly associated with greater suicide risk, particularly for acute time periods (i.e., 0–10 days) (Petridou et al., 2002; Vyssoki et al., 2012, 2014; Papadopoulos et al., 2005). Vyssoki et al. (2012) have proposed that the impact of sunlight on serotonin neurotransmission, such as increasing metabolism and transporter density (Praschak-Rieder et al., 2008), may trigger impulsivity and promote suicide-related behavior.
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Effects of sunshine on suicide rates

Abstract

Objectives

Methods

Results

Conclusions

Introduction

Section snippets

Methods

Results

Discussion

Conclusion

Biol Psychiatry

Lancet

Biol Psychiatry

Neuropsychopharmacology

J Psychiatr Res

Compr Psychiatry

Soc Sci Med

Psychiatry Res

J Affect Disord

J Affect Disord

Psychiatry Res

Soc Sci Med

Psychiatry Res

J Affect Disord

J Affect Disord

Neuropsychobiology

Psychiatry Res

Effect of different photoperiod exposure on [3H]imipramine binding and serotonin uptake in the rat brain

J Neurochem

Seasonal variation in human brain serotonin transporter binding

Arch Gen Psychiatry

Enhanced serotonin transporter function during depression in seasonal affective disorder

Neuropsychopharmacology