Seasonal and circadian rhythms in suicide in Cagliari, Italy

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. (C) 1999 Elsevier Science B.V. All rights reserved.