Influence of Method on Seasonal Distribution of Attempted Suicides in Italy

Abstract

To verify if attempted suicides follow different seasonal distributions according to the method chosen, we studied the Italian monthly distribution of admissions for attempted suicide in the period 1984–1995 according to gender and age, distinguishing between non-violent (ICD 950–952) and violent (ICD 953–958) attempted suicides. The effect of temperature was also taken into account. A clear asymmetry in seasonal distribution of events can be observed in the oldest age groups in both genders, with a peak in warmer months. Only male attempted suicides by violent methods show a clear asymmetry in seasonal distribution, with a peak in spring months and a trough in autumn months. Spectral analysis, more accurate in detecting seasonal rhythms than analyses that only compare monthly seasonal means, identifies a circannual rhythm for violent suicides in both genders. The seasonal components of total variance in attempted suicides account for 16.5 and 12.4%, respectively, of violent male and female attempted suicides. Among males, a significant (p < 0.05) 4 cycles/year pattern is seen alongside the more relevant (89.4%, p < 0.01) 1 cycle/year distribution. Among females, aside from the 1 cycle/year distribution (63.3%, p < 0.01) noted, a 6 cycles/year pattern is found to contribute significantly (16.9%, p < 0.05) to the seasonal component of variance. A clear relationship with temperature indicators is noted among males: higher temperatures positively correlate with attempted suicides, whereas cooler temperatures seem to exert a protective action. Female attempts show a less evident correlation with indicators of temperature. Sample composition by age and gender and the lack of distinction between methods of attempted suicide may have obscured the seasonal component of some classes of attempted suicide in previous studies. The circannual rhythm found in this study of violent attempted suicide in relation to climate seasonal change confirms the importance of taking chronobiological variables into account in the evaluation of patients at risk of suicide.

Seasonality and Climatic Associations with Violent and Nonviolent Suicide: A Population-Based Study

“…This finding is consistent with the seasonality of violent suicide attempts in Italy, suggesting a positive relationship between temperatures and violent suicide attempts [28] . Further, no climatic parameter is significant for nonviolent suicide.…”

Effects of temperature variation on suicide in five U.S. counties, 1991–2001

“…does not clear up the confusion about the effects of weather on suicide. There are other studies with no obvious methodological problems that directly contradict each other (Chew and McCleary 1995;Geltzer et al 2000;Lambert et al 2003;Lester 1999;Linkowski et al 1992;Preti and Miotto 2000;Zung et al 1974). Some of these authors identify positive correlations between weather variables and suicides, some identify negative correlations, and some identify no correlations.…”

“…In addition, suicides are quite rare, even among groups of people that are considered to be at a higher risk of committing suicide (Sher 2004). Regardless, many studies have identified significant relationships between suicide and atmospheric variables Lambert et al 2003;Nicholls et al 2006;Partonen et al 2004a;Preti 1997;Preti and Miotto 2000;Salib 1997).…”

“…This could be attributed to the fact that some studies analyze multiple (as many as 46) meteorological variables (Deisenhammer 2003). For instance, some of the numerous studies correlating suicide with temperature claim to find an increase in the number of suicides when temperatures are colder (Linkowski et al 1992;Souêtre et al 1990; Thorson and Kasworm 1984;Tietjen and Kripke 1994) while most find just the opposite (Breuer et al 1986;Deisenhammer et al 2003;Lester 1986;Maes et al 1994;Preti and Miotto 2000;Salib 1997;Salib and Gray 1997;Souêtre et al 1987). Further, most studies show that suicide rates vary according to season with the most common peak occurring in late spring or early summer (Deisenhammer et al 2003;Lambert et al 2003;Parker and Walter 1982;Partonen et al 2004a;Preti 1997;Preti and Miotto 2000).…”

Seasonal variation in blood concentrations of interleukin-6, adrenocorticotrophic hormone, metabolites of catecholamine and cortisol in healthy volunteers

“…Cold weather has been shown to alter blood pressure, sympathetic tone, procoagulatory factors, C-reactive protein (CRP) and mood (Woodhouse et al 1994;Kawahara et al 1989). Several investigators have also reported seasonal variations in the incidence of coronary artery disease (CAD) and seasonal affective disorder (SAD), which peak in winter (Moschos et al 2004;Westrin and Lam 2007), and higher suicide rates in warmer months (Preti and Miotto 2000). There is also a predominance of mood disorders in the summer among the Asian population (Ozaki et al 1995;Han et al 2000) as well as in tropical Australia (Morrissey et al 1996).…”