Research reportSeasonal and circadian rhythms 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.
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