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Suicide Seasonality: Theoretical and Clinical Implications
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Neuroscience.
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Background: Although suicide seasonality has been well-documented, surprisingly little is known about its underlying mechanisms.

Methods: In this thesis, data from three Swedish registers (Cause of Death Register, National Patient Register, Prescribed Drugs Register) and data from the Swedish Meteorological and Hydrological Institute were used.

In Study I, the amplitude of suicide seasonality was estimated in completed suicides in 1992-2003 in individuals with different antidepressant medications or without antidepressants.

In Study II, monthly suicide and sunshine data from 1992-2003 were used to examine the association between suicide and sunshine in groups with and without antidepressants.

In Study III, the relationship between season of initiation of antidepressant treatment and the risk of suicidal behavior was explored in patients with a new treatment episode with antidepressant medication.

In Study IV, the complex association between sunshine, temperature and suicidal behavior was investigated in patients with a new treatment episode with an antidepressant in two exposure windows (1-4 and 5-8 weeks) before the event.

Findings: Study I: Higher suicide seasonality was found in individuals treated with selective serotonin reuptake inhibitors (SSRIs) compared with those given a different antidepressant treatment or those without any antidepressant treatment.

Study II: In individuals treated with SSRIs, there was a positive association between sunshine and suicide, with the association stronger in men treated with SSRIs compared with men treated with other antidepressants. An effect modification by age was observed.

Study III: The elderly (65+) had a higher risk of suicide when initiating antidepressant treatment in summer and a higher risk of suicide attempt when starting antidepressant therapy in spring and summer. Younger patients (0-24) demonstrated a higher risk of suicide attempt when treatment was initiated in autumn.

Study IV: In the elderly (65+), a harmful association was observed between the risk of suicide attempt and the average daily temperature during the four weeks before the suicide attempt, as well as with average daily sunshine during both exposure windows (1-4 and 5-8 weeks) before the suicide attempt.

Significance: Our results provide epidemiological support for the role of the serotonergic system in seasonality of suicide in which both medication and climate may be involved.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2017. , p. 74
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Medicine, ISSN 1651-6206 ; 1383
Keywords [en]
suicide, season, antidepressants, sunshine, temperature
National Category
Neurosciences
Research subject
Psychiatry
Identifiers
URN: urn:nbn:se:uu:diva-330907ISBN: 978-91-513-0108-2 (print)OAI: oai:DiVA.org:uu-330907DiVA, id: diva2:1149335
Public defence
2017-12-07, Gunnesalen, Ing 10, Akademiska sjukhuset, Uppsala, 13:00 (Swedish)
Opponent
Supervisors
Available from: 2017-11-16 Created: 2017-10-15 Last updated: 2018-03-07
List of papers
1. Suicide seasonality and antidepressants: a register-based study in Sweden
Open this publication in new window or tab >>Suicide seasonality and antidepressants: a register-based study in Sweden
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2013 (English)In: Acta Psychiatrica Scandinavica, ISSN 0001-690X, E-ISSN 1600-0447, Vol. 127, no 2, p. 117-125Article in journal (Refereed) Published
Abstract [en]

Objective

Seasonality of completed suicides with a peak in spring and early summer is a well-documented finding. The circannual serotonergic functioning is hypothesized to be central in this phenomenon. Antidepressant medications exert their pharmacological action mainly by regulating serotonin. Our aim is to study the amplitude of the seasonal effect among suicide victims positive for different classes of antidepressants or without any antidepressants at the time of death.

Method

By using Swedish Registers, 12 448 suicides with forensic data for antidepressive medication and information on in-patient-treated mental disorder were identified during 1992-2003. Seasonality was estimated with a Poisson regression variant of the circular normal distribution of completed suicides.

Results

Higher suicide seasonality was found for individuals treated with selective serotonin reuptake inhibitor (SSRIs) compared to those with other antidepressant treatment or without any antidepressant treatment. The finding is more evident for men and violent suicide methods and those without history of in-patient treatment.

Conclusion

Our results provide preliminary support for the serotonergic hypothesis of suicide seasonality and raise the question of a possible accentuation of the natural suicide seasonality in patients treated with SSRIs, a hypothesis that warrants further investigation.

National Category
Psychiatry
Identifiers
urn:nbn:se:uu:diva-189178 (URN)10.1111/j.1600-0447.2012.01891.x (DOI)000313492300004 ()22676408 (PubMedID)
Available from: 2012-12-25 Created: 2012-12-25 Last updated: 2017-12-06Bibliographically approved
2. Serotonergic medication enhances the association between suicide and sunshine
Open this publication in new window or tab >>Serotonergic medication enhances the association between suicide and sunshine
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2016 (English)In: Journal of Affective Disorders, ISSN 0165-0327, E-ISSN 1573-2517, Vol. 189, p. 276-281Article in journal (Refereed) Published
Abstract [en]

Background: An association between suicide and sunshine has been reported. The effect of sunshine on hormones and neurotransmitters such as serotonin has been hypothesized to exert a possible triggering effect on susceptible individuals. The aim of this study is to examine if there is an association between sunshine and suicide, adjusting for season, and if such an association differs between individuals on different antidepressants. Methods: By using Swedish Registers and the Swedish Meteorological and Hydrological Institute we obtained information, including forensic data on antidepressive medication for 12,448 suicides and data on monthly sunshine duration. The association between monthly suicide and sunshine hours was examined with Poisson regression analyses while stratifying for sex and age and controlling for time trend and season. These analyses were repeated in different groups of antidepressant treatment. Results: We found a significantly increased suicide risk with increasing sunshine in both men and women. This finding disappeared when we adjusted for season. Among both men and women treated with selective serotonin reuptake inhibitors (SSRIs) there was a positive association between sunshine and suicide even after adjustment for season and time trend for suicide. Pair comparisons showed that the sunshine-suicide association was stronger among men treated with SSRIs compared to other antidepressant medications or no medication at all. Limitations: Other meteorological factors were not controlled (i.e. temperature) for in the analyses. Conclusions: There is an enhanced association between sunshine and suicide among those with SSRI medication, even after adjusting for season. This may have interesting theoretical and clinical implications.

Keywords
Seasonality, Suicide, Serotonin
National Category
Psychiatry
Identifiers
urn:nbn:se:uu:diva-269956 (URN)10.1016/j.jad.2015.09.056 (DOI)000364170200041 ()26454332 (PubMedID)
Available from: 2015-12-19 Created: 2015-12-19 Last updated: 2017-12-01Bibliographically approved
3. Season of treatment initiation with antidepressants and suicidal behavior: A population-based cohort study in Sweden
Open this publication in new window or tab >>Season of treatment initiation with antidepressants and suicidal behavior: A population-based cohort study in Sweden
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2017 (English)In: Journal of Affective Disorders, ISSN 0165-0327, E-ISSN 1573-2517, Vol. 215, p. 245-255Article in journal (Refereed) Published
Abstract [en]

Background: Decreased binding capacity of SERT in the prefrontal cortex has been observed in both suicide victims and suicide attempters. Moreover, some studies have shown that SERT has a seasonal variation with lower binding capacity in the spring and summer, which coincides with a seasonal peak of suicides. Our aim was to explore whether the season of treatment initiation with antidepressants is associated with suicide or suicide attempt and compare it with the underlying suicide seasonality in the general population.

Methods: Using Swedish registers, patients who initiated treatment with an antidepressant were followed up to three months for suicidal behavior. Cox regression analyses were used.Results were compared with the underlying seasonal pattern by calculating standardized mortality ratios (SMRs) for suicides and standardized incidence ratios (SIRs) for suicide attempts.

Results: Patients aged years had higher risk for suicide when initiating antidepressant treatment in the summer, and also a higher risk for suicide attempt when initiating treatment in the spring and summer. Young patients (0-24 years) presented a higher risk for suicide attempt when initiating treatment in the autumn. Patients with previous suicide attempt had a seasonal pattern, with a higher risk to carry out a suicide attempt in the summer and autumn. Results from the SMR and SIR calculations numerically support these findings.

Limitations: We used information of filling an antidepressant prescription as a proxy of actual antidepressant treatment. Patients with combination, augmentation therapy or those switching antidepressant during followup were excluded. Thus, our results refer to less complicated psychopathology.

Conclusions: Our results indicate an interaction between biological and health care-related factors for the observed seasonal pattern of suicidal behavior in the elderly, whereas psychological and societal factors may be more important for the seasonality observed in the younger patients.

Place, publisher, year, edition, pages
ELSEVIER SCIENCE BV, 2017
National Category
Psychiatry
Identifiers
urn:nbn:se:uu:diva-326206 (URN)10.1016/j.jad.2017.03.028 (DOI)000401213300034 ()28343052 (PubMedID)
Funder
Swedish Society of Medicine, SLS-175701
Available from: 2017-08-07 Created: 2017-08-07 Last updated: 2017-10-15Bibliographically approved
4. Sunshine, temperature and suicidal behavior in patients treated with antidepressants: an explorative nested case control study.
Open this publication in new window or tab >>Sunshine, temperature and suicidal behavior in patients treated with antidepressants: an explorative nested case control study.
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Background

The association of suicide and suicide attempts with climatic factors has been investigated in the past with contradicting results.

Objective

Our aim in this article is to explore if different exposure windows for sunshine or temperature are associated with increased suicidal behavior, measured by suicide and attempted suicide, among people starting an antidepressant treatment.

Methods

By using Swedish registers and daily data about temperature and sunshine duration, we explored the association of sunshine and temperature and suicidal behavior in two exposure windows in patients treated with antidepressants between July 2007 and December 2011. From a source population of 784 792 patients, 307 completed and 1674 attempted suicides were included as cases in the conditional logistic regression analyses, while controlling for potential confounders, including season, as well as temperature and hours of sunshine when these variables were not the main exposure variable. Ten controls were matched to each case using risk-set sampling. In stratified case control analyses by season, age, and sex were conducted using regression models with interaction terms.

Results

There was no overall association between temperature or sunshine with suicidal behavior. However, in stratified analyses, a statistically significant effect modification between age and average daily temperature/sunshine during the last four weeks was discovered for the outcome of suicide attempt (p=0.001 and 0.017 respectively). Amongst older patients (65+) an increase of one hour in the average daily sunshine during the last four weeks was associated with an 8% increase in the rate of suicide attempt. In the same age group, an increase of one degree Celsius in the average daily temperature during the weeks 1-4 was associated with a 3% increase in the rate of suicide attempt.

Conclusions

Despite the absence of an overall association between sunshine and temperature and suicidal behavior, our results point to a possible effect modification by age, with higher risk of suicide attempts found only in the older age groups.

Keywords
suicide, season, sunshine, temperature, antidepressants
National Category
Natural Sciences
Research subject
Psychiatry
Identifiers
urn:nbn:se:uu:diva-330905 (URN)
Available from: 2017-10-15 Created: 2017-10-15 Last updated: 2017-10-15

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