Research report
Seasonal and circadian rhythms in suicide in Cagliari, Italy

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Abstract

Background. In previous studies of the seasonality of suicide, peaks have often been found in the number of suicides in the spring and early summer in both northern and southern hemispheres. The purpose of the present study was to investigate the distribution of suicide as to month, seasons, day of the week, and time of the day. Method. Data on suicides in Cagliari (Italy) in the period 1990–1994 were analyzed by means of spectral analysis, cosinor and multiple regression analysis. Results. Two seasonal rhythms, i.e. an annual and a semiannual rhythm, accounted for 25% of the variation in the total number of suicides. The peak number of suicides occurred in February with a second less significant peak in June and July. Lows were found in November and December. There were no significant differences in number of suicides in relation to days of the week. Three rhythms, i.e. 24 hours (circadian), 8 hours and 1 hour, explained 63.9% of the variance in the number of suicides by time of the day. Peak numbers in number of suicides were found between 08:31 and 12:30h, while the number of suicides was also significantly higher between 12:31h and 20:30h than between 20.31h and 8.30h. Age and gender did not significantly affect the seasonal and circadian rhythms in suicide. Conclusions. The results show that there is a significantly seasonal variation and a highly significant variation by time of the day in suicide in Cagliari, Italy.

Introduction

Various factors have been identified as being associated with suicide. The majority of people who commit suicide appear to be psychiatrically ill, with depression, alcoholism, and schizophrenia the most common disorders (Barraclough et al., 1974, Rich et al., 1988). Associations have also been found between suicide and other predisposing factors such as physical disorders (Kaplan et al., 1994), negative life events and lack of social support (Kuda, 1988), dysfunctional coping mechanisms (Gutscher, 1988), certain personality traits, i.e., the tendency towards impulsivity and violence (Plutchnik and Van Praag, 1989), borderline and antisocial personality disorders (Runeson and Beskow, 1991), sociodemographic and socioeconomic factors, and a previous history or familial history of suicidal behavior (Barraclough et al., 1974).

Seasonal variation in the occurrence of suicide has been described (Aschoff, 1981). As far as is known, the first comparative study of monthly suicide rates was published by Morselli in 1879 (Morselli, 1881). He noted that the number of suicides per month gradually rose from the beginning of the year to June, when a peak was reached followed by a decrease towards the end of the year. From this finding, Morselli concluded that the incidence of suicide is influenced by meteorological factors; that it was not so much the absolute temperature but the change in temperature in the spring and early summer which influences individuals not yet acclimatized. Durkheim (1951)criticized this assertion in 1897 in his book 'Le Suicide'. Based on the relationship between the monthly incidence of suicide and the duration of daylight, and on the fact that suicide occurs more frequently during the day than during the night, Durkheim presumed that the duration of daylight was a determining factor in the yearly distribution of suicides.

Table 1 gives an overview of studies in Europe, North America and South Africa in which statistical processing of the data showed monthly variations in suicide rates. In the majority of these studies, the maximum number of suicides occurred in Spring and the minimum in Winter.

The first known systematic investigation into the weekly distribution of suicide was published in 1835 by De Guerry (De Guerry, 1835). Using data collected in France, he found that suicide was committed with a relatively greater frequency from Monday to Thursday than during the rest of the week. The greatest number of suicides occurred in the beginning of the working week, the most on Mondays, and the least on Saturdays (Nayha, 1980, Zung and Green, 1974, Rogot et al., 1976, Lester, 1979, Bollen and Philips, 1982, Massing and Angermeyer, 1985). Israel is an exception, with the most on Sundays, and the least on Fridays (Modan et al., 1970). A significant variation by time of the day for suicide (peaks in the morning) and parasuicide (peaks in late afternoon) has been found in some studies (Motohashi, 1990, Maldonado and Kraus, 1991, Caracciolo et al., 1996, Gallerani et al., 1996).

The aims of the present study were: (i) to analyze the monthly variation in the number of suicides and to determine the presence or absence of yearly or yearly-based rhythms; (ii) to analyze the weekly distribution of suicides; and (iii) to determine whether there is a circadian rhythm in the committing of suicide in Cagliari, Italy.

Section snippets

Collection of data

The data on suicides committed between 01/01/1990 and 31/12/1994 in Cagliari, the capital city of the island of Sardinia (Italy) were obtained from the Ministry of Justice in Cagliari. The following information was obtained for each victim: age and gender, date and time of the suicidal act (not of death), and the manner in which suicide was committed. For the manner in which suicide was committed (ICD-9, World Health Organization, 1977), a distinction was made between non-violent means: E950,

General

From 1990 to 1994, 355 suicide victims were registered in Cagliari, of which 21.7% were female and 78.3% were male. This agrees with previous descriptions (Kaplan et al., 1994), which established that men commit suicide more than three times more often than women. It is also of note that there was a yearly increase in the number of suicides from 47 in 1990 to 94 in 1994, which amounts to a doubling in the yearly number of suicides in 5 years. Fig. 1 shows the actual, mean monthly number of

Discussion

The first finding of the present study reflects a definite correlation between the month of the year and the number of suicides in Cagliari, with the highest mean number in February and a second significantly higher value in June and July. The results show that there is a significant seasonal variation with annual and semiannual rhythms, which account for 25% of the variation in number of suicides.

These results partially agree with previously reported studies (see Introduction, Table 1), in

Acknowledgements

The research reported was supported in part by the Clinical Research Center for Mental Health, Antwerp, Belgium; and the IRCCS, Istituto Fatebenefratelli, Brescia; Italy. The secretarial assistance of Mrs. M. Maes and Mrs. C. Robertson is greatly appreciated.

References (61)

  • G.H. Tietjen et al.

    Suicides in California (1968–1977): absence of seasonality in Los Angeles and Sacramento Counties

    Psychiatry Res.

    (1994)
  • Aschoff, J., 1981. Annual rhythms in man. In: Aschoff, J. (Ed.), Handbook of Behavioral Neurobiology, Biological...
  • B.M. Barraclough et al.

    Monthly variation of suicidal, accidental and undeterminated poisoning deaths

    Br. J. Psychiatry

    (1978)
  • B.M. Barraclough et al.

    A hundred cases of suicide: clinical aspects

    Br. J. Psychiatry

    (1974)
  • C. Bingham et al.

    Inferential statistical methods for estimating and comparing cosinor parameters

    Chronobiologia

    (1982)
  • K.A. Bollen et al.

    Imitative suicides: a national study of the effects of television news stories

    Am. Sociol. Rev.

    (1982)
  • A. Carlsson et al.

    Seasonal and circadian monoamine variations in human brains examined post-mortem

    Acta Psychiatr. Scand.

    (1980)
  • S. Caracciolo et al.

    Circadian rhythm of parasuicide in relation to violence of method and concomitant mental disorder

    Acta Psychiatr. Scand.

    (1996)
  • G. Cerbus

    Seasonal variation in some mental health statistics: suicides, homicides, psychiatric admission, and institutional placement of the retarded

    J. Clin. Psychol.

    (1970)
  • R. Danneel

    Der einfluss geophysikalischer faktoren auf die selbstmordhaufigkeit

    Arch. Psychiatr. Nervenkrankh.

    (1974)
  • De Guerry, 1835. Statistique Morale de la France....
  • F. De Meyer et al.

    Spectral resolution of cardiocirculatory variations in men measured by autorhythmometry over 2 years

    Int. J. Biometeorol.

    (1991)
  • P. D'Hondt et al.

    Seasonal variation in paroxetine binding to platelets in normal volunteers: relationships to climatic factors

    Neuropsychopharmacology

    (1996)
  • K.W. Dixon et al.

    A statistical investigation into the relationship between meteorological parameters and suicide

    Int. J. Biometeorol

    (1983)
  • Durkheim, E., 1951. Suicide: a Study in Sociology. Free Press, New...
  • M. Gallerani et al.

    The time for suicide

    Psychol. Med.

    (1996)
  • M. Gostynski et al.

    Meteotrope aktivitat der wetterlage und ihre rolle in der selbstmord-epidemiologie

    Zentbl. Bakt. Parasit. Kde.

    (1975)
  • Gutscher, H., 1988. Beyond the regulation of emotion. In: Moller, H.-J., Schmidtke, A., Welz, R. (Eds.), Current Issues...
  • Haus, E., Touitou, Y., 1992. Principles of clinical chronobiology. In: Touitou, Y., Haus, E. (Eds.), Biologic Rhythms...
  • P.K. Jones et al.

    Lunar association with suicide

    Suicide Life Threat. Behav.

    (1977)
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