Journal ofAffectice Disorders, 25 (1992) 161-166 0 1992 E’ievier Science Publishers B.V. All rights reserved 01650327/92/$05.00

161

JAD 00906

e climatic factors on viole t and non-violent suici

Paul Linkowski a, Fraqoise

Martin a and Viviane De Maertelaer

b

u Department of Psychiatry and ’ Section on Biostatistics (IRIBI-IN), IGpital Erasme, Unioersite’Libre de BruveUes, Brussels, Belgium (Received 6 January 1992) (Revision received 19 March 1992) (Accepted 24 March 1992)

Summary We explored the differential effect of some climatic factors such as temperature, atmospheric pressure, sunlight duration and humidity grade on the temporal distribution of violent and non-violent suicides, accidental and undetermined causes of death as well as homicides in Belgium, between 1969 and 1984. Our study indicates that temperature and sunlight duration are specifically associated with the probability of violent suicide, while deaths due to non-violent causes (such as non-violent suicides) did not show any relationship to climatic factors.

Key words: Suicide; Climate; Belgium -

Introductiotn A relationship between seasons and suicidal behaviour has been the focus of long-term interest in psychiatric research. According to the most extensive studies (Wenz, 1977; Eastwood and Peacocke, 1976; Aschoff, 1981; Myha, 1983; Souetre et al., 19871, the annual rhythm of suicides seems to he correlated (instantaneously or with

Corre.qpondence to: Paul Linkowski, Department of Psychiatry, Hhpital Erasme, Route dc Lennik 808. 1070 Bruxelles. Belgium

some lag) with climatic variables such as daytime or sunlight duration and with ambient temperature (Souetre et al., 1987; Souetre et al., 1990). This author clearly shows that the seasonal distribution of completed suicides in France was highly correlated with ambien> iemperature and sunlight duration. The aim of the present study is to further explore the differential effect of certain climatic factors on death probabilities in Belgium between 1969 and 1984. The deaths studied are those due :o suicides, accidental and undetermined causes (by distinguishing violent from non-violent acts) and to homicides.

162

and Methods

Subjects

The tour climatic factors explored were ambient temperature, atmospheric pressure, sunlight duration as well as humidity grade. Monthly averages of these factors were obtained from the Belgian National institute of Meteorology for a 192 months period ranging from 1969 to 1984. For the same time period, monthly numbers of total male and female deaths in Belgium were provided by the Belgian National Institute of Statistics. Among those, the number of monthly deaths due to the following seven causes was separately recorded, according to the 9th International Classification of Diseases (JCD). 1) Violent suicides (JCD, E 951-959) 2) Non-violent suicides (ICD, E 950) violent causes 3) Deaths from undetermined (ICD, E 981-989) 4) Deaths from undetermined non-violent causes (ICD, E 980) 5) Accidental violent deaths (JCD, E 810-829, 867-869, 880-888, 890-899. 910-929) 6) Accidental non-violent deaths (JCD E 850858, 860-866) 7) Homicides (ICD, E 960-969). The proportions of monthly deaths due to these specific cac:;es were separately calculated in men and women, giving thus 14 time series of 192 data. These proportions were compared between men and women, for each cause, with the use of non-parametric ann-Whitney tests. Stepwise logistic regressions were performed on each of the 14 death probabilities sets of data in order to detect whether they could be influenced by some of the climatic factors under study. TABLE Death

In iogistic regression, the predicted proportion of deaths is assumed to follow the logistic model: exp(u)/(l -I-exp(u)) where 11 is a linear function of the climatic factors. 1 he logistic regressions separately considered the first four and the last four years period (the global set of 192 months could not be analysed at one time, since exceeding the software capacities). In the stepwise method, a factor is considered to have a significant effect when the improvement in the chisquare due to its introduction leads to a P-value lower than 0.05. At the end of the stepwise procedure, the logistic regression model is rejected when the Goodness-of-fit chi-square leads to a lower than 0.05 P-value. I he time dependence of each death probability and each climatic condition was further investigated on the 192 month-period with univariate spectral analyses. Bivariate spectral analyses were then performed in order to detect possible crosscorrelations between each death probability and each climatic condition (computations were performed using the BMDP statistical software). T!re primary objective of spectral analysis is to decompose a time-varying quantity into a sum (or integral) of sine and cosine functions. These functions are the ‘building blocks’ from which we can construct periodic functions. Spectral analysis is thus an analysis in the frequency domain of a given time series. It is the name given to methods of estimating the spectral density function (or ‘spectrum’) of the time series. The spectral density function describes how the variation in a time series may be accounted for by cyclic components at different frequencies. Seasonal variations can be detected since producing peaks at the seasonal frequencies and at integer multiples of it. When

1 proportions

expressed as percentages of all deaths (mean +StiM)

m men and women and P-le\sls

after statistical

comparison Causes of death

Men

Non-violent

0.210)

‘Aolent

Non-violent Violent

suicides

suicides deaths due to undel;r.

deaths due to undetermined

Homicides Non-violent Violent

lined causes causes

accidental deaths

P-value

02x4 * O.OOY

< 0.001

1.I95 f 0,02Y

0.868 * !).016

< O.(lOl

0.029 + 0.002

0.041 + 0.002

< 0.00

0.120 + 0.004

0.078 + 0.003

0); * P < 0.05 * * P < 0.01.

significant: P < 0.001 the goodness cf fit test led to P = 0.826). This was observed in the last four year-period. 2) In men, the death probability due to violent undetermined causes was shown tu illcreaPc with sunlight duration (The improvelllent of x2 due to that climatic variable was statistically highly significant: f = 0.001; the goodness of fit test ied to P = 0.555). This was observed in the first four year-period.

periodicity was hoyever detected when the violent causes were cdnsidered (extent for the violent undetermined causes, in women). The relationship between the death probabilities due to ~Eolent causes and each ciimatic factors were furt r investigated with bivariate spe:*tral ana!ysc:b he statistically significant effects are as follow.>: The death are positive!,. and negati\pc sexes. Cross served with

probabilities due to violent suicides correlated tc the humidity grade y to the sunligh? duration in both correlations of lag 4 are also obt atmospheric pressure in both humidity, ambient temperature and sunlight duration in men only. They are positive with hck-!ity grade and negative otherwise (Table 3;. The temlyoral distribution of violent suicides in me3 and women, in Belgium, between 1969 and 1984, is illustrated in Fig. 1.

After univariate spectral analysis, each climatic factor showed an evident 12 month periodicity and a positive autocorrelation of lag 1. Spectral analyses performed on death probabilities due to the non-violent causes or homicides concluded to the absence of yearly periodic&y Yn both sexes for both fatalities. This is in close agreement with the absence of relationship with the climatic factors, as reported above. A yearly

W!OLENT SUICIDES IN MEN AND WOMEN

3.2

(BELGIUM

1969 -1984)

1

MEN

WOMEN

1

25

Fig. 1. Temporaldistribution

49

I

I

I

73

97

121

I 145

169

TIME (MONTHS) of suicides in Belgium (mean monthly values) In m;n and women, between 1969-1984.

165

The probabilities of violent deaths due to undetermined causes show no instantaneous correlations with the climatic factors. Lagged cross correlatii_ms with the atmospheric pressure are observed in men (negative; lags I and 3) and in women (positive; lag 8) (Table 3). The probabilities of violent deaths due to accidental causes are positively correlated to the ambient temperature in men. A negative cross correlation of lag 3 is observed with humidity (and, as expected, a positive one with sunlight duration) in women (Table 3). Discussion The main finding from this study is that some climatic factors such as humidity grade and sunlight duration specifically affect the probability of violent suicide, while non-violent suicides as well as deaths due to homicides or some other nonviolent causes do not show any relationship to climatic factors in Belgium. In particular, death probabilities due to violent suicide were positively correiated to the humidity grade and negatively to the sunlight duration (based on monthly mean values), in both sexes. We restricted our study to Belgium, a small country where the climatic conditions might be considered as relatively homogenous, and performed the analysis over a long time series period of fifteen years (1969-1984) which increased the power of the analysis. Our study adds to previous observations reported by Souetre and his group (1987, 1990) showing that in France the seasonal distribution of suicides covaried negatively with ambient temperature and sunlight duration. We further report that the effect of both climatic parameters is specifically restricted to violent suicidal behaviour, in contrast to non-violent suicides. Additional analyses from our study tend to demonstrate that other death causes which might be compared to suicides such as undetermined or accidental deaths do not, in general, show any instantaneous correlation with climatic factors, with the exception of violent deaths due to accidental causes which were positively correlated with ambient temperature in man. Interestingly, homicide, another violent cause of death, did not

show any climatic related variation a finding already supported by Cerbus (1970) observations in Ohio (USA). However, in our study, while some of the cfimatic variabies have been shown to be related to violent death probabihtits, they could generaliy not satisfactorily explain them as shown by the logistic regression modei including the four cIimatic factors (with the exception for the probability of violent suicides which was shown to increase with ambient temperature, but on one four year period and in women only). Clearly other psychopathological and/or sociological parameters might also operate, as suggested by Souetre et ai. (1990) who showed that inclusion of some additional parameters such as alcoholism and percentage of the population working might confound the interpretation of the effect of climatic factors. Our study also adds to Souetre et al. (1990), observations pointing out the (previously undescribed) positive correlation between violent suicide and humidity grade and also showing further that climatic factors clearly had no influence on suicides due to non-violent causes. The reIationship between climate and suicides has been investigated by severai authors, but they explored in general short-term daily association between suicide and weather variable (in contrast to a long-term study of the impact of weather on suicide); (see Eastwood and Peter, 1990 and Souetre et al., 1987). In this respect Pokomy et al. (1963) as well as Zung and Green (1974) failed to observe any clear relationship between daily suicides and temperature and/or rainfall measures. As far as tentative biological explanations are concerned, low CSF 5 HIAA has been suggested as an indicator of vulnerability to violent suicidality in depressed patients (Asberg et al., 1986). Seasonal rhythms have been reported for CSF 5 HIAA in normal subjects (Brewerton et al., 1988) as well as in depressed patients (Asberg et al., ‘1980).

Depressed patients have been also shown to present with higher CSF 5 HIAA leve!s during July-August than during September-October (Asberg et al., 1980). However this speculation remains tentative. Our study did not confirm Lester’s (1986) or Souetre et al. (1990) con-

tentions that ambient temperature correlated with completed suicides. We observed ratller, that in men, death probabilities due to violent suicides cross correlated with a negative lag of four months. Thus, delayed, rather than instantaneous climatic modifications might also influence violent suicidal behaviour.

We thank 1. Mazza for secretarial study was supported by a grant A.N.A.H.-Rotary.

help. This from the

eferences Aschoff. J. (1981) Annual rhythms in man. In: J. Aschoff (Ed.), Handbook of Behavioural Neurology Plenum Press New York, pp. 475-487. Asberg, M., Bertilsson, L., Rydin, E., Schalling, D., Thoren, P. and Traskman-Bendz, L. (1980) Monoamine mctabolites in cerebra-spinal fluid in relation to depressive illness, suicidal behavior and personality. In: B. Angrisi, G.D. Burrows, M. Lader, 0. Lingjaerde. G. Sedrale and D. Wheatley. (Eds). Recent advances in neuropharmacology. Pergamon Press. Oxford, pp. 257-267. Asberg, M., Nordstriim, P. and Traskman-Bendz. L. (1986) Biological factors in suicide. In: A. Roy. (Ed.). Suicide. Williams and Wilkins, Baltimore, 47-73.

Brewerton. T., Berettini, W., Nurnberger, J. and Linnoil?., M. (1988) Analysis of seasonal fluctuations of CSF monoamine metabolites and neuropeptides in normal controls findings with 5 HIAA and HVA. Psychiatr. Res. 23, 257-265. Cerbus. G. (1970) Seasonal variation in some mental health statistics suicides, homicides, psychiatric admissions and institutional placement of the retarded. J. Clin. Psycbol. 26, 61-63. Eastwood, M.R. and Peacocke. J. (1976) Seasonal patterns of suicide, depression and electroconvulsion therapy. Br. J. Psychiatr. 129. 472-475. Eastwood, M.R. and Peter. A.M. (1988) Epidemiology and seasonal affective disorder. Psychol. Med. 18. 799-806. Lester, D. (1986) Suicide and homicide rates: their relationship to latitude and longitude and to weather. Suicide Life Threat. Behbviour 16, 356-359. Niiyha, S. (19821 Autumn incidence of suicides re-examined: deta from Finland by sex. age and occupation. Br. J. Psychiatr. 141, 512-517. Pokorny, A.D., Davis. F. and Haberson. W. (1963) Suicides suicide attempts and weather. Am. J. Psychihtr. 120. 377381. Souetre, E., Salvati E., et al. (1987) Seasonality of suicides environmental. sociological acd biological covariations. J. Affect. Disord. 13, 215-225. Souctre, E., Wehr, T.A. et al. (1990) Influence of environmental factors on suicidal behaviour. Psychiatr. Res. 32, 253263. Wenz F.V. (1977) Effects of seasons and sociological variables .m suicidal behaviour. Public Health Rep, 92, 233-239. Zung, W. and Green, R. (1974) SeasonaZ variation of suicide and depression. Arch Gen. Psychiatr. 30, X9-91.

Effect of some climatic factors on violent and non-violent suicides in Belgium.

We explored the differential effect of some climatic factors such as temperature, atmospheric pressure, sunlight duration and humidity grade on the te...
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