Research reportCyclic time patterns of death from suicide in northern Finland
Introduction
Suicides are not evenly distributed over particular periods of time, since social or psychological factors have immediate or delayed effect on the individual’s decision to commit suicide (Mann, 1998). Most studies have found that suicide rates tend to peak during spring and summer Yip et al., 1998, Altamura et al., 1999. Moreover, it appears that climate and weather conditions can somewhat influence the occurrence of death from suicide, possibly by interacting with social factors Preti, 1997, Salib and Gray, 1997, Preti and Miotto, 1998.
Physical time-givers, as well as social and endogenous ones, can modify complex behaviours. Seasonal transition may contribute to the pathogenesis of the suicide process due to the substantial changes in day length and temperature that occur in spring and autumn. The asynchrony between changes in temperature and light–dark cycles challenges the stability of endogenous clocks (Czeisler et al., 1999). It may acutely result in disordered periods of activity (Taillard et al., 2001), or disorganised behaviour, possibly leading to suicide in adverse circumstances.
Since geophysical factors may markedly influence daily behaviour patterns, it is important in terms of prevention to study whether they can also affect the occurrence of death from suicide. We therefore set out to study the time series of death from suicide in the population of a far northern region where there is extensive variation in levels of ambient temperature and daylight over the year. We hypothesised that increasing light exposure on still cold days during spring in specific may drive the individual into a later activity phase and the failure to adjust to time-giving signals from the natural habitat during this period of seasonal mismatch may lead to death from suicide more frequently than by chance alone.
Section snippets
Methods
The study material consisted of all suicides (n=1658) committed from 1 April 1987 to 31 December 1999 in the province of Oulu, which is located 64–66°N in northern Finland, a northern European country with approximately 5 million inhabitants. Date, sex and age were recorded for each case. Population data on the number of inhabitants, sex ratio and age groups in the province during the study period were derived from statistical yearbooks published by Statistics Finland (1988–2000).
Cause of death
Results
Of the 1413 male and 313 female suicides there were complete data available for analysis on 1658 (96%) subjects (Table 1). Male sex (χ2=735.3, df=1, P<0.0000001) and two older age groups (30–60, plus over 60 years, χ2=344.7, df=2, P<0.0000001) were associated with the risk of suicide. Our analyses showed that marked changes in the number of suicides occurred during the study period (χ2=28.0, df=12, P=0.01). The risk of suicide decreased significantly over the three consecutive years from 1994
Discussion
Our main finding was that contrary to recently published findings Yip et al., 2000, Parker et al., 2001 there was a significant seasonal variation in death from suicide. The highest incidence was observed at the turn of summer to autumn, and a second peak occurred during spring. Our findings also suggest that despite a marked difference in time patterns for suicide between men and women in the long term, there is none in the seasonal variation.
The seasonal effect was modest though, as compared
Conclusion
Marked changes in the number of deaths from suicide were observed during the study period. There was a substantial seasonal variation in suicide occurrence among the study population. Compared to sex and age, however, the seasonal effect on the risk of suicide remained modest. Periods of seasonal mismatch, local weather conditions, and geomagnetic storms had no effect on the risk.
Acknowledgments
We thank Heikki Nevanlinna, PhD, from the Finnish Meteorological Institute, for help with the interpretation of geomagnetic data, and Markus Henriksson, MD, from the National Public Health Institute, for intellectual support.
References (38)
- et al.
Seasonal and circadian rhythms in suicide in Cagliari, Italy
J. Affect. Disord.
(1999) - et al.
Lunar rhythms of the meal and alcohol intake of humans
Physiol. Behav.
(1995) - et al.
How a circadian clock adapts to seasonal decreases in temperature and day length
Neuron
(1999) - et al.
Psychiatric illness and risk factors for suicide in Denmark
Lancet
(2000) The influence of seasonal change on suicidal behaviour in Italy
J. Affect. Disord.
(1997)- et al.
Seasonality in suicides: the influence of suicide method, gender and age on suicide distribution in Italy
Psychiatry Res.
(1998) - et al.
Decreasing tendency of seasonality in suicide may indicate lowering rate of depressive suicides in the population
Psychiatry Res.
(1998) - et al.
A re-examination of seasonal variation in suicides in Australia and New Zealand
J. Affect. Disord.
(1998) - et al.
The genetic background of individual variations of circadian-rhythm periods in healthy human adults
Am. J. Hum. Genet.
(1993) - et al.
Accuracy of circadian entrainment under fluctuating light conditions: contributions of phase and period responses
J. Biol. Rhythms
(1999)
Locally-weighted regression: an approach to regression analysis by local fitting
J. Am. Stat. Assoc.
STL: a seasonal-trend decomposition procedure based in loess
J. Official Statistics
Stability, precision, and near-24-h period of the human circadian pacemaker
Science
Seasonal patterns of suicide, depression and electroconvulsive therapy
Br. J. Psychiatry
Suicides and the lunar cycle
Psychol. Rep.
Suicide as an outcome for mental disorders: a meta-analysis
Br. J. Psychiatry
Mental disorders and comorbidity in suicide
Am. J. Psychiatry
Light-induced suppression of endogenous circadian amplitude in humans
Nature
Seasonality comparison among groups using incidence data
Biometrics
Cited by (56)
Evaluation of the Suicide Attempt Surveillance System in Santiago de Cali, Colombia, 2016–2019
2023, Revista Colombiana de PsiquiatriaTemporal distribution of suicide mortality: A systematic review
2018, Journal of Affective DisordersThe association between space weather conditions and emergency hospital admissions for myocardial infarction during different stages of solar activity
2016, Journal of Atmospheric and Solar-Terrestrial PhysicsBirthdays are associated with an increased risk of suicide in Japan: Evidence from 27,007 deaths in Tokyo in 2001-2010
2016, Journal of Affective DisordersSeasonality of suicide behavior in Northwest Alaska: 1990–2009
2016, Public HealthThe effect of solar-geomagnetic activity during hospital admission on coronary events within 1 year in patients with acute coronary syndromes
2013, Advances in Space ResearchCitation Excerpt :The increased MI morbidity 2–3 days before CIR-derived GS also conforms to the results of Dimitrova et al. (2009). One of the mechanisms of the influence of geomagnetic activity on human health may be Schumann resonance (Cherry 2002; Partonen et al. 2004) and ULF pulsations Pc1–Pc5 (Kleimenova et al., 2007; Zenchenko et al., 2010). Schumann resonances (SR) are resonant electromagnetic waves in the cavity between the Earth and the ionosphere with a fundamental frequency about 8 Hz.