#
2002 Martin Dunitz Ltd
International Journal of Psychiatry in Clinical Practice 2002 Volume 6 Pages 39 ± 44
39
Month of birth and suicide: An exploratory study EMAD SALIB Honorary Senior Lecturer, Liverpool University; Consultant Psychiatrist, Hollins Park Hospital, Warrington
OBJECTIVE :
To explore the association between suicide and month of
birth. Data were extracted from records of the Public Health Department in North Cheshire between 1989 and 2000. `Suicide’ refers to all deceased who were the subjects of coroner’s inquests resulting in a verdict of suicide or an open verdict. The month of birth of all who died of natural causes and were reported during a 2-year period was obtained from the Public Health Department in North Cheshire for comparison. METHOD :
There were 502 incidents of suicide in North Cheshire during the 12-year period. Significant differences were found between suicides and deaths due to natural causes, with an increase of incidents of suicide in those born in the month of May (w2 23, d.f.11, P50.01). The distribution of suicide by hanging appeared to be significantly higher in those born in September and July and lowest in those born in November compared with what would expected by chance (w2 28, d.f.11, P50.005). Those who died by violent means were more likely to have been born in the summer. The difference between the observed and expected numbers of suicides by methods other than hanging failed to reach statistical significance. RESULTS :
The results, though inconclusive, are interesting, particularly in view of recent reports that persons born during the winter ± spring months had significantly lower values of 5-HIAA, and also reports of low CSF levels of 5-HIAA in persons with violent suicidal behaviour such as hanging, stabbing, firearms, or jumping from heights and impulsivity. A biological explanation of suicidal behaviour could have implications for our understanding of the psychopathol ogy of suicide and eventually offer new strategies for treatment and prevention. The conflicting reports from different countries within the northern hemisphere indicate the need for future studies with adequate design and acceptabl e statistical power. (Int J Psych Clin Pract 2002; 6: 39 ± 44) CONCLUSION :
Correspondence Address Emad Salib, MB, MSc, MRCPI, FRCPsych, Hollins Park Hospital, Warrington WA2 8WA Tel: 01925 664123 Fax: 01925 664145
Received 3 May 2001; revised 4 June 2001; accepted 11 June 2001
Keywords month of birth hanging season of birth
INTRODUCTION
T
he season of birth has been reported to influenc e human physiologic al development al processe s such as birthweight and age at menarche.1 Some studies have also shown that month of birth may be a predisposin g factor for several diseases, raising the possibilit y that very early environment al influences are involved . A seasonal
suicide violent suicide
pattern of birth has been suggested for glaucoma,2 allergy, 3 asthma4 and acute leukaemia in infancy.5 An effect of birth date has also been reported in achievements in sport, universit y recruitment and scientific innovation, suggesting that particular birth months may confer advantages.6 Seasonalit y of birth has been shown to vary significantl y with social class particularl y in upper class births.7
40
E Salib
The season of birth for sufferers from several psychiatri c disorders has been investigate d repeatedly, but hypotheses and suggested mechanisms have proved inconclusi ve. The findings of 81 of these studies, reviewed by Castrogiovann i and colleagues , confirmed that more patients with schizophrenia are born in December and January.8 Findings for affective disorders are not clear, but alcohol dependence, autism and dyslexia appear to be reported more frequently in those born during spring and summer months. Very few studies have investigated a possible link between month of birth and suicide rates. Ellswort h reported that the distribution of birth month of those who committed suicide was different from that for those who did not.9 Pokorny found an over-represe ntation of suicide cases born in the month of July.1 0 Studies by Sanborn & Sanborn1 1 and Lester 1 2 did not confirm such an association. Kettl and colleagues reported small variations in the season of birth for suicides among Alaska natives, with summer births showing more suicides.1 3 Chotai and colleague s examined a register of all those who had committed suicide in the county of VaÈsterbotten in northern Sweden from 1952 to 1993 and found that those born during February to April were significantl y more likely than those born in other months to have used hanging rather than poisoning or carbon monoxide as a method of suicide. The reverse was said to be true for those born during October to January.1 4 This present study examines the association between suicide and month of birth over a 12-year period in North Cheshire, in an attempt to replicate the results of Chotai et al, 1 4 and also compares the month-of-birt h distributio n of suicides with that of death due to `natural causes’.
METHOD Data were extracted from the records of deaths of the Public Health Department in North Cheshire between January 1989 and April 2000. North Cheshire has a population of 350,000, with an average suicide rate of 11 per 100,000. `Suicide’ refers to all deceased who were the subjects of coroner’s inquests resulting in a verdict of suicide or an open verdict. The month of birth of all who died of natural causes reported during 1993 and 1994 was obtained from the Public Health Department in North Cheshire. It was not possible to match the cases by obtaining equal mean age and variance of the two groups by gender because of the relatively younger age of those who committed suicide. Goodness of fit w2 , with the P-value, was used to test whether the observed distribution for suicides differed significantl y from the expected distribution (the `expected distribution’ in this study refers to the distributio n of deaths due to natural causes). The percentages in the results section refer to the month-of-birt h proportion of deaths due to suicide as a whole and due to specific methods of suicide.
Two-by-two tables were also used to compare violent and non-violent suicide for the four quarters FebruaryApril, May-July, August-October and November-January. Goodness of fit w2 was computed by SPSS PC (Version 5). The proportions were compared by using Statcalc and Epicalc functions of Epi info statistical package (Version 5).
RESULTS There were 502 incidents of suicide in North Cheshire during the 12-year period. The main methods of suicide in the sample were: overdose 194 (39%), hanging 136 (27%), drowning 35 (7%); car exhaust 59 (12%); shooting 10 (2%); immolation 4 (1%); wounding 13 (2.5%); asphyxia 14 (3%); jumping from a height 17 (4%); electrocution 5 (1%); and hit by a train 15 (3%). The month of birth and cause of death of persons who died from natural causes (6951) over a 2-year period (1993 and 1994) were obtained from death tapes in the North Cheshire Public Health Department for comparison. Monthly frequencie s and proportions of all cases of suicide (502) and deaths due to natural causes (6951) were used. There was no association between month of birth and month of death, whether due to suicide or natural causes (k P40.05), with 7.5% of deaths coinciding with month of birth. Twenty-five percent of deaths due to suicide occurred within one month before or after the month of birth, compared to 23% in those who died naturally (P40.05). Table 1 shows the distribution of all deaths by month of birth. Goodness of fit w2 was used to detect the significan t variations within the 12 months, comparing the actual and the expected number of cases for each month of birth with chance occurrence under the null hypothesis. Significant difference s were found in the suicide data: there was an increase of incidents of suicide in those born in the month of May (w2 23, d.f. 11, P50.01), but this was only significan t in male victims (w2 22, d.f. 11, P50.05). The distributio n of the 502 cases according to the month of birth was then compared with the expected number of cases, i.e. the distribution of the deaths due to natural causes, according to the month of birth (Figure 1). The observed distributio n of suicides according to month of birth proved to be significant ly differen t from the expected distribution of natural deaths in North Cheshire (w2 25.4, d.f. 11, P50.01). Figure 2 shows the distribution of suicide by hanging, according to month of birth; it appears to be significantl y higher for those born in September and July and lowest for those born in November, as compared to what would be expected by chance (w2 28, d.f. 11, P50.005). To ensure that significant deviations in certain months were not due to the effect of chance, the distribution of the season of birth was examined for the four quarters of the year (Figure 3). The high occurrence of hanging, together
Birth month and suicide
41
Table 1 Proportion of deaths due to natural causes and suicide in North Cheshire by month of birth Month of birth Jun Jul
Cause of death, %
Jan
Feb
Mar
Apr
May
Natural causes w2 =18, d.f. 11, P=0.08
8.5
8
9.3
8.6
8.4
8.4
Suicide 9.2 w2 =23, d.f. 11, P50.01 Overdose 13.4 w2 =16, d.f. 11, P=0.1 Hanging 5.9 w2 =28, d.f. 11, P50.005 Drowning 11.4 w2 =6, d.f. 11, P=0.8 Car exhaust 5.1 w2 =17, d.f. 11, P=0.1 Other methods 6.4 w2 =12, d.f. 11, P=0.4
8
6.4
9.6
12.2
9.3
7.7
8.2
5.1
9.6
5.7
7
Month of birth in England & Wales 1988±1998 Mean in thousands 53.4 Monthly, % 8.4
Aug
Sep
Oct
Nov
Dec
8.3
9
7.8
8.2
7.5
8.1
6.6
9.4
7.6
10.6
8
6
6.8
12.9
8.2
6.2
6.7
7.7
6.2
5.2
8.2
8.8
8.1
7.4
12.5
10.3
16.2
10.3
1.5
4.4
10.1
8.6
5.7
8.6
5.7
8.6
5.7
14.3
8.6 3.4
11.9
3.4
3.4
11.9
18.6
1.7
8.5
6.8
10.2
10.2
7.7
2.6
9
14.1
5.1
12.8
5.1
11.5
7.7
9
9
48.8 7.7
53.6 8.4
52.4 8.2
53.0 8
53.1 8.3
56.4 8.9
54.4 8.6
55.3 8.7
53.6 8.4
50.1 7.9
51.6 8.1
with low reports of overdosing , for those born during August to October, and fewer incidents of hanging for those born during November to January, are striking. The difference between the numbers of observed and expected suicides using methods other than hanging failed to reach statistical significanc e. Table 2 examines the proportion of months of birth of men and women in respect of the two main categories of suicide referred to as: (a) non-violent death, including self poisoning by solid or liquid (E950), gas in domestic use (E951) and other gases and vapours (E952); and (b) predominant ly violent death, which included all methods other than self-poisoni ng (E953 ± hanging, strangulatio n and suffocation ; E954 ± drowning; E955 ± firearms and explosives ; E956 ± cutting or piercing instruments; E957 ± jumping from a high place; E958 ± other methods). A higher frequency of non-violent suicide was observed in men born in January and in women born in May. Those who died by violent means were more likely to have been born in the summer, in all cases. Figures 4 and 5 show the distribution of month of birth in violent and non-violent suicide compared to the expected distribution (deaths due to natural causes). To find out whether the month-of-birt h distribution of violent or non-violent death deviates significantl y from that of death due to natural causes, w2 analysis of the 2612 table of non-violent vs natural causes was carried out. For nonviolent methods, there was no significant differenc e (w2 17, d.f. 11, P40.05). However, when violent suicides and deaths due to natural causes were compared, the result was highly significan t (w2 27.7, d.f. 11, P50.01). Table 1 would
Percent 14 12 10 8 6 4 2 0
JAN FEB MAR APR MAY JUN
JUL AUG SEP OCT NOV DEC
Suicide Natural causes
Figure 1 Distribution of death due to natural causes and suicide, by month of birth, in North Cheshire, 1989-2000
suggest that this differenc e might be mainly due to cases of suicide by hanging.
DISCUSSION METHODOLOGICAL LIMITATIONS The main limitations of this study are: (1) the small sample size and limited duration of data collection is likely to
42
E Salib
reduce its statistical power; (2) the suicide data collected came from only one geographica l area, which may not be representativ e of the UK population or of other countries in the northern hemisphere ; (3) there was no information regarding country of birth or any pre-natal, natal or postnatal complications that might have confounded the findings; (4) matching of suicide cases and death due to natural causes in respect of equal mean age by gender was not possible because of the relatively young age of those who committed suicide compared to those who died naturally.
INTERPRETATION OF THE FINDINGS Several studies have found low CSF and urinary levels of the monoamine metabolites 5-hydroxyin doleacetic acid (5HIAA), homovanilli c acid (HVA) and methohydrox y
Percent 20
phenylgylco l (MHPG) in persons suffering from suicidal behaviour, impulsivit y and depression .1 5,1 6 Low CSF levels of 5-HIAA have been found in persons showing violent suicidal behaviour such as hanging, stabbing, firearms or jumping from heights and impulsivity ,1 6,1 7 and in patients who are at increased risk of future suicide or suicide attempt.1 8 Low CSF levels of 5-HIAA have also been found in depressed patients with high lethality or well-planne d suicide attempts, as compared to other persons making suicide attempts.1 7 Chotai and Asberg reported some significan t season-of-bi rth variations in 5-HIAA and HVA levels in the CSF for a sample of drug-free Swedish patients adjusted for sex, age, height and diagnostic category.1 9 Persons born during the months February to April had significant ly lower values of 5-HIAA. The values of HVA, as well as the ratio of HVA/5-HIAA and HVA/MHPG, were significantl y higher for those born during the winter months (October to January) . Moreover, season of birth has also been found to be associated with certain aspects of suicidal behaviour. One of the objectives of the study was to see if it could replicat e the results of Chotai et al,1 4 which showed that
15 40 10
Percent
30 20
5 10 0
JAN
FEB MAR APR MAY JUN
JUL AUG SEP OCT NOV DEC
Suicide by hanging Natural causes
Figure 2 Distribution of suicide by hanging and death due to natural causes, by month of birth, in North Cheshire, 1989-2000
Table 2 Month of birth and nature of suicide by gender in North Cheshire 1989±2000
0 Feb–Apr
May–Jul 1: natural causes; 3: hanging;
Nov– Jan
2: suicide; 4: overdose.
Figure 3 Season of birth and number of suicides in North Cheshire, 1989-200 0
Non-violent suicides Male Female % (n) % (n) January February March April May June July August September October November December
Aug– Oct
15.8 (23) 8.9 (13) 8.2 (12) 6.8 (10) 11.6 (17) 8.9 (13) 5.5 (8) 7.5 (11) 7.5 (11) 6.8 (10) 4.1 (6) 8.2 (12)
6.3 (3) 10.4 (5) 6.3 (3) 12.5 (6) 16.7 (8) 6.3 (3) 8.3 (4) 4.2 (2) 8.3 (4) 4.2 (2) 8.3 (4) 8.3 (4)
All violent suicides Male Female % (n) % (n) 13.6 (17) 12.8 (16) 9.4 (11) 20.9 (26) 23.7 (30) 11.8 (14) 22.3 (27) 16.5 (20) 26.2 (32) 21.0 (26) 12.3 (16) 9.4 (12)
9.6 (3) 17.3 (6) 23.3 (6) 17.3 (6) 19.4 (6) 7.7 (3) 22.4 (8) 16.8 (5) 25.3 (6) 9.1 (2) 10.3 (4) 21.3 (6)
Birth month and suicide
14
Percent
14
Percent
12
12
10
10
8
8
6
6
4
4
2 0
2 0
43
Natural causes Non Violent suicide JAN FEB MAR APR MAY JUN
JUL AUG SEP OCT NOV DEC
Natural causes Violent suicide
JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC
8.5 8.3 9.3 8.6 8.4 8.4 8.3 9 7.8 8.2 7.5 8.1 13.4 9.3 7.7 8.2 12.9 8.2 6.2 6.7 7.7 6.2 5.2 8.2
Figure 5 Distribution of deaths due to non-violent suicide and to natural causes, by month of birth, in North Cheshire, 1989-2000
Figure 4 Distribution of deaths due to violent suicide and to natural causes, by month of birth, in North Cheshire, 1989-2000
among those who had committed suicide, those born during October to January had, compared to other suicides, significantl y more often employed an overdose rather than hanging as the suicide method. By examining Table 1 for the 502 suicides, we see that in all 194 used an overdose and 136 hanging. Of the 194 overdose cases, 64 were born during October to January; of the 136 hanging cases, 30 were born during October to January. Chi-squar e analysis with a 262 table, with birth season (Oct-Jan, Feb-Sept) vs method (overdose, hanging) , gives w2 4.16 (d.f. 1) with continuity correction (P50.05). So the present study does replicate this result. However, Chotai et al found that among those who had committed suicide, persons born during February to April had significantl y more often employed hanging rather than overdose than did those born in May to January. Similar analysis of 49 overdose cases born during February to April, and 32 hanging cases born during February to April, yielded a chi-squar e value of 0.1 (1 d.f.), which is not significant . So the present study cannot replicate this result. The Swedish findings of season-of-bi rth variations in the serotonin metabolite 5-hydroindo leacetic acid (5HIAA) may be applicable to suicide incidents, mostly of non-violent deaths, in North Cheshire involving those born in winter months. However, in this sample, the incidence of suicides as a whole, regardles s of the method used, appeared to be significantl y higher in those born in May. Violent methods of suicide, particularl y hanging, more frequently go with summer birth dates, quite the reverse of the Swedish results. Perhaps the only conclusion that can be drawn from studies such as this is that seasonalit y of birth in those who commit suicide may reflect the timing of some subtle abnormalities in an early neural migration or differentiatio n process, which might underlie a person’s constitutiona l
vulnerabilit y. A biological basis for suicidal behaviour is possible , as factors that could influenc e brain growth a few months after gestation could affect sensorimotor , cognitive, affective and behavioura l development . This suggestion gives some hope that development al approaches might prove important for understandin g of the psychopathol ogy of depression and suicidal behaviour, and offer new strategies for treatment and prevention.
KEY POINTS . Significant difference s were found among suicides, compared to deaths due to natural causes, with more suicides in those born in May. The distribution of suicide by hanging appeared to be significantl y higher in those born in September and July and lowest in those born in November. . Recent reports suggest that persons born during the winter and spring have significantl y lower values of 5-HIAA, and that low levels of 5-HIAA have been found in persons showing violent suicidal behaviour. . Small sample size and the undetermined study power may limit the inferentia l value of the study. . If suicidal tendencies are affected by biology, there is hope that developmenta l approaches might prove important. . The conflicting findings from different countries in the northern hemisphere indicate the need for future studies.
44
E Salib
Attempts to search for environment al and climatic links with suicide are likely to raise more questions than answers, but seem to follow a consistent pattern, pointing to the constitutional make-up of an individual . The conflicting findings between studies from different countries from the northern hemisphere seem to indicate the need for future multinationa l studies with adequate design, sample size and acceptable statistical power.
ACKNOWLEDGEMENTS The author is grateful to Tracy Flute, Jake Abbas and North Cheshire Health for their help in data collection. My thanks also to Miss Bernie Hayes, Chief Librarian at Hollins Park and Mrs Janet Davies from Pfizer for their support and Miss Katie Spencer for help in data entry and preparation of the manuscript.
REFERENCES 1. Richter J (1990) Does the month of birth affect human biological development processes? Arztl Jugendkd 81: 55 ± 58. 2. Weale R (1993) Is the season of birth a risk factor in glaucoma? Br J Ophthalmol 77: 214 ± 217. 3. Troise C, Voltolini S, Delbono G (1989) Allergy to Parietaria pollen and month of birth. Allergol Immunopathol 17: 201 ± 204. 4. Aberg N (1989) Birth season variation in asthma and allergic rhinitis. Clin Exp Allergy 19: 643 ± 648. 5. Meltzer AA, Spitz MR, Johnson CC, Culbert SJ (1989) Seasonof-birth and acute leukaemia of infancy. Chronobiol Int 6: 285 ± 289. 6. Bell JF, Massey A (1994) The significance of birth dates. Nature 382: 666. 7. James WH (1971) Social class and season of birth. J Biosoc Sci 3: 309 ± 320. 8. Castrogiovanni P, Iapichino S, Pacchierotti C, Pieraccini F (1998) Season of birth in psychiatry: A review. Neuropsychobiology 37: 175 ± 181. 9. Ellsworth H (1938) Season of birth: Its relation to human abilities. New York: Wiley. 10. Pokorny AD (1960) Characteristics of 44 patients who subsequently committed suicide. Arch Gen Psychiatry 3: 314 ± 323. 11. Sanborn DE, Sanborn CJ (1974) Suicide and months of birth. Psychol Rep 34: 950.
12. Lester D (1987) Month of birth of suicides, homicides and natural deaths. Psychol Rep 60: 1310. 13. Kettl PA, Collins T, Sredy M, Bixler EO (1997) Seasonal differences in suicide in birth rate in Alaska natives compared to other populations. Am Indian Alsk Native Mental Health Res 8: 1 ± 10. 14. Chotai J, Salander R, Jacobsson L (1999) Season of birth associated with age and method of suicide. Arch Suicide Res 5: 245 ± 254. 15. Lester D (1995) The concentration of neurotransmitter metabolites in the cerebrospinal fluid of suicidal individuals: A meta-analysis. Pharmacopsychiatry 28: 45 ± 50. 16. Asberg M (1997) Neurotransmitters and suicidal behaviour. The evidence from cerebrospinal fluid studies. Ann NY Acad Sci 836: 158 ± 181. 17. Mann JJ, Malone KM (1997) Cerebrospinal fluid amines and higher-lethality suicide attempts in depressed in-patients. Biol Psychiatry 41: 162 ± 171. 18. Nordstorm P, Samuelsson M, Asberg M et al (1994) CSF 5HIAA predicts suicide risk after attempted suicide. Suicide Life Threat Behav 24: 1 ± 9. 19. Chotai J, Asberg M (1999) Variations in CSF monoamine metabolites according to the season of birth. Neuropsychobiol 249: 57 ± 62.
2002 Martin Dunitz Ltd
International Journal of Psychiatry in Clinical Practice 2002 Volume 6 Pages 39 ± 44
39
Month of birth and suicide: An exploratory study EMAD SALIB Honorary Senior Lecturer, Liverpool University; Consultant Psychiatrist, Hollins Park Hospital, Warrington
OBJECTIVE :
To explore the association between suicide and month of
birth. Data were extracted from records of the Public Health Department in North Cheshire between 1989 and 2000. `Suicide’ refers to all deceased who were the subjects of coroner’s inquests resulting in a verdict of suicide or an open verdict. The month of birth of all who died of natural causes and were reported during a 2-year period was obtained from the Public Health Department in North Cheshire for comparison. METHOD :
There were 502 incidents of suicide in North Cheshire during the 12-year period. Significant differences were found between suicides and deaths due to natural causes, with an increase of incidents of suicide in those born in the month of May (w2 23, d.f.11, P50.01). The distribution of suicide by hanging appeared to be significantly higher in those born in September and July and lowest in those born in November compared with what would expected by chance (w2 28, d.f.11, P50.005). Those who died by violent means were more likely to have been born in the summer. The difference between the observed and expected numbers of suicides by methods other than hanging failed to reach statistical significance. RESULTS :
The results, though inconclusive, are interesting, particularly in view of recent reports that persons born during the winter ± spring months had significantly lower values of 5-HIAA, and also reports of low CSF levels of 5-HIAA in persons with violent suicidal behaviour such as hanging, stabbing, firearms, or jumping from heights and impulsivity. A biological explanation of suicidal behaviour could have implications for our understanding of the psychopathol ogy of suicide and eventually offer new strategies for treatment and prevention. The conflicting reports from different countries within the northern hemisphere indicate the need for future studies with adequate design and acceptabl e statistical power. (Int J Psych Clin Pract 2002; 6: 39 ± 44) CONCLUSION :
Correspondence Address Emad Salib, MB, MSc, MRCPI, FRCPsych, Hollins Park Hospital, Warrington WA2 8WA Tel: 01925 664123 Fax: 01925 664145
Received 3 May 2001; revised 4 June 2001; accepted 11 June 2001
Keywords month of birth hanging season of birth
INTRODUCTION
T
he season of birth has been reported to influenc e human physiologic al development al processe s such as birthweight and age at menarche.1 Some studies have also shown that month of birth may be a predisposin g factor for several diseases, raising the possibilit y that very early environment al influences are involved . A seasonal
suicide violent suicide
pattern of birth has been suggested for glaucoma,2 allergy, 3 asthma4 and acute leukaemia in infancy.5 An effect of birth date has also been reported in achievements in sport, universit y recruitment and scientific innovation, suggesting that particular birth months may confer advantages.6 Seasonalit y of birth has been shown to vary significantl y with social class particularl y in upper class births.7
40
E Salib
The season of birth for sufferers from several psychiatri c disorders has been investigate d repeatedly, but hypotheses and suggested mechanisms have proved inconclusi ve. The findings of 81 of these studies, reviewed by Castrogiovann i and colleagues , confirmed that more patients with schizophrenia are born in December and January.8 Findings for affective disorders are not clear, but alcohol dependence, autism and dyslexia appear to be reported more frequently in those born during spring and summer months. Very few studies have investigated a possible link between month of birth and suicide rates. Ellswort h reported that the distribution of birth month of those who committed suicide was different from that for those who did not.9 Pokorny found an over-represe ntation of suicide cases born in the month of July.1 0 Studies by Sanborn & Sanborn1 1 and Lester 1 2 did not confirm such an association. Kettl and colleagues reported small variations in the season of birth for suicides among Alaska natives, with summer births showing more suicides.1 3 Chotai and colleague s examined a register of all those who had committed suicide in the county of VaÈsterbotten in northern Sweden from 1952 to 1993 and found that those born during February to April were significantl y more likely than those born in other months to have used hanging rather than poisoning or carbon monoxide as a method of suicide. The reverse was said to be true for those born during October to January.1 4 This present study examines the association between suicide and month of birth over a 12-year period in North Cheshire, in an attempt to replicate the results of Chotai et al, 1 4 and also compares the month-of-birt h distributio n of suicides with that of death due to `natural causes’.
METHOD Data were extracted from the records of deaths of the Public Health Department in North Cheshire between January 1989 and April 2000. North Cheshire has a population of 350,000, with an average suicide rate of 11 per 100,000. `Suicide’ refers to all deceased who were the subjects of coroner’s inquests resulting in a verdict of suicide or an open verdict. The month of birth of all who died of natural causes reported during 1993 and 1994 was obtained from the Public Health Department in North Cheshire. It was not possible to match the cases by obtaining equal mean age and variance of the two groups by gender because of the relatively younger age of those who committed suicide. Goodness of fit w2 , with the P-value, was used to test whether the observed distribution for suicides differed significantl y from the expected distribution (the `expected distribution’ in this study refers to the distributio n of deaths due to natural causes). The percentages in the results section refer to the month-of-birt h proportion of deaths due to suicide as a whole and due to specific methods of suicide.
Two-by-two tables were also used to compare violent and non-violent suicide for the four quarters FebruaryApril, May-July, August-October and November-January. Goodness of fit w2 was computed by SPSS PC (Version 5). The proportions were compared by using Statcalc and Epicalc functions of Epi info statistical package (Version 5).
RESULTS There were 502 incidents of suicide in North Cheshire during the 12-year period. The main methods of suicide in the sample were: overdose 194 (39%), hanging 136 (27%), drowning 35 (7%); car exhaust 59 (12%); shooting 10 (2%); immolation 4 (1%); wounding 13 (2.5%); asphyxia 14 (3%); jumping from a height 17 (4%); electrocution 5 (1%); and hit by a train 15 (3%). The month of birth and cause of death of persons who died from natural causes (6951) over a 2-year period (1993 and 1994) were obtained from death tapes in the North Cheshire Public Health Department for comparison. Monthly frequencie s and proportions of all cases of suicide (502) and deaths due to natural causes (6951) were used. There was no association between month of birth and month of death, whether due to suicide or natural causes (k P40.05), with 7.5% of deaths coinciding with month of birth. Twenty-five percent of deaths due to suicide occurred within one month before or after the month of birth, compared to 23% in those who died naturally (P40.05). Table 1 shows the distribution of all deaths by month of birth. Goodness of fit w2 was used to detect the significan t variations within the 12 months, comparing the actual and the expected number of cases for each month of birth with chance occurrence under the null hypothesis. Significant difference s were found in the suicide data: there was an increase of incidents of suicide in those born in the month of May (w2 23, d.f. 11, P50.01), but this was only significan t in male victims (w2 22, d.f. 11, P50.05). The distributio n of the 502 cases according to the month of birth was then compared with the expected number of cases, i.e. the distribution of the deaths due to natural causes, according to the month of birth (Figure 1). The observed distributio n of suicides according to month of birth proved to be significant ly differen t from the expected distribution of natural deaths in North Cheshire (w2 25.4, d.f. 11, P50.01). Figure 2 shows the distribution of suicide by hanging, according to month of birth; it appears to be significantl y higher for those born in September and July and lowest for those born in November, as compared to what would be expected by chance (w2 28, d.f. 11, P50.005). To ensure that significant deviations in certain months were not due to the effect of chance, the distribution of the season of birth was examined for the four quarters of the year (Figure 3). The high occurrence of hanging, together
Birth month and suicide
41
Table 1 Proportion of deaths due to natural causes and suicide in North Cheshire by month of birth Month of birth Jun Jul
Cause of death, %
Jan
Feb
Mar
Apr
May
Natural causes w2 =18, d.f. 11, P=0.08
8.5
8
9.3
8.6
8.4
8.4
Suicide 9.2 w2 =23, d.f. 11, P50.01 Overdose 13.4 w2 =16, d.f. 11, P=0.1 Hanging 5.9 w2 =28, d.f. 11, P50.005 Drowning 11.4 w2 =6, d.f. 11, P=0.8 Car exhaust 5.1 w2 =17, d.f. 11, P=0.1 Other methods 6.4 w2 =12, d.f. 11, P=0.4
8
6.4
9.6
12.2
9.3
7.7
8.2
5.1
9.6
5.7
7
Month of birth in England & Wales 1988±1998 Mean in thousands 53.4 Monthly, % 8.4
Aug
Sep
Oct
Nov
Dec
8.3
9
7.8
8.2
7.5
8.1
6.6
9.4
7.6
10.6
8
6
6.8
12.9
8.2
6.2
6.7
7.7
6.2
5.2
8.2
8.8
8.1
7.4
12.5
10.3
16.2
10.3
1.5
4.4
10.1
8.6
5.7
8.6
5.7
8.6
5.7
14.3
8.6 3.4
11.9
3.4
3.4
11.9
18.6
1.7
8.5
6.8
10.2
10.2
7.7
2.6
9
14.1
5.1
12.8
5.1
11.5
7.7
9
9
48.8 7.7
53.6 8.4
52.4 8.2
53.0 8
53.1 8.3
56.4 8.9
54.4 8.6
55.3 8.7
53.6 8.4
50.1 7.9
51.6 8.1
with low reports of overdosing , for those born during August to October, and fewer incidents of hanging for those born during November to January, are striking. The difference between the numbers of observed and expected suicides using methods other than hanging failed to reach statistical significanc e. Table 2 examines the proportion of months of birth of men and women in respect of the two main categories of suicide referred to as: (a) non-violent death, including self poisoning by solid or liquid (E950), gas in domestic use (E951) and other gases and vapours (E952); and (b) predominant ly violent death, which included all methods other than self-poisoni ng (E953 ± hanging, strangulatio n and suffocation ; E954 ± drowning; E955 ± firearms and explosives ; E956 ± cutting or piercing instruments; E957 ± jumping from a high place; E958 ± other methods). A higher frequency of non-violent suicide was observed in men born in January and in women born in May. Those who died by violent means were more likely to have been born in the summer, in all cases. Figures 4 and 5 show the distribution of month of birth in violent and non-violent suicide compared to the expected distribution (deaths due to natural causes). To find out whether the month-of-birt h distribution of violent or non-violent death deviates significantl y from that of death due to natural causes, w2 analysis of the 2612 table of non-violent vs natural causes was carried out. For nonviolent methods, there was no significant differenc e (w2 17, d.f. 11, P40.05). However, when violent suicides and deaths due to natural causes were compared, the result was highly significan t (w2 27.7, d.f. 11, P50.01). Table 1 would
Percent 14 12 10 8 6 4 2 0
JAN FEB MAR APR MAY JUN
JUL AUG SEP OCT NOV DEC
Suicide Natural causes
Figure 1 Distribution of death due to natural causes and suicide, by month of birth, in North Cheshire, 1989-2000
suggest that this differenc e might be mainly due to cases of suicide by hanging.
DISCUSSION METHODOLOGICAL LIMITATIONS The main limitations of this study are: (1) the small sample size and limited duration of data collection is likely to
42
E Salib
reduce its statistical power; (2) the suicide data collected came from only one geographica l area, which may not be representativ e of the UK population or of other countries in the northern hemisphere ; (3) there was no information regarding country of birth or any pre-natal, natal or postnatal complications that might have confounded the findings; (4) matching of suicide cases and death due to natural causes in respect of equal mean age by gender was not possible because of the relatively young age of those who committed suicide compared to those who died naturally.
INTERPRETATION OF THE FINDINGS Several studies have found low CSF and urinary levels of the monoamine metabolites 5-hydroxyin doleacetic acid (5HIAA), homovanilli c acid (HVA) and methohydrox y
Percent 20
phenylgylco l (MHPG) in persons suffering from suicidal behaviour, impulsivit y and depression .1 5,1 6 Low CSF levels of 5-HIAA have been found in persons showing violent suicidal behaviour such as hanging, stabbing, firearms or jumping from heights and impulsivity ,1 6,1 7 and in patients who are at increased risk of future suicide or suicide attempt.1 8 Low CSF levels of 5-HIAA have also been found in depressed patients with high lethality or well-planne d suicide attempts, as compared to other persons making suicide attempts.1 7 Chotai and Asberg reported some significan t season-of-bi rth variations in 5-HIAA and HVA levels in the CSF for a sample of drug-free Swedish patients adjusted for sex, age, height and diagnostic category.1 9 Persons born during the months February to April had significant ly lower values of 5-HIAA. The values of HVA, as well as the ratio of HVA/5-HIAA and HVA/MHPG, were significantl y higher for those born during the winter months (October to January) . Moreover, season of birth has also been found to be associated with certain aspects of suicidal behaviour. One of the objectives of the study was to see if it could replicat e the results of Chotai et al,1 4 which showed that
15 40 10
Percent
30 20
5 10 0
JAN
FEB MAR APR MAY JUN
JUL AUG SEP OCT NOV DEC
Suicide by hanging Natural causes
Figure 2 Distribution of suicide by hanging and death due to natural causes, by month of birth, in North Cheshire, 1989-2000
Table 2 Month of birth and nature of suicide by gender in North Cheshire 1989±2000
0 Feb–Apr
May–Jul 1: natural causes; 3: hanging;
Nov– Jan
2: suicide; 4: overdose.
Figure 3 Season of birth and number of suicides in North Cheshire, 1989-200 0
Non-violent suicides Male Female % (n) % (n) January February March April May June July August September October November December
Aug– Oct
15.8 (23) 8.9 (13) 8.2 (12) 6.8 (10) 11.6 (17) 8.9 (13) 5.5 (8) 7.5 (11) 7.5 (11) 6.8 (10) 4.1 (6) 8.2 (12)
6.3 (3) 10.4 (5) 6.3 (3) 12.5 (6) 16.7 (8) 6.3 (3) 8.3 (4) 4.2 (2) 8.3 (4) 4.2 (2) 8.3 (4) 8.3 (4)
All violent suicides Male Female % (n) % (n) 13.6 (17) 12.8 (16) 9.4 (11) 20.9 (26) 23.7 (30) 11.8 (14) 22.3 (27) 16.5 (20) 26.2 (32) 21.0 (26) 12.3 (16) 9.4 (12)
9.6 (3) 17.3 (6) 23.3 (6) 17.3 (6) 19.4 (6) 7.7 (3) 22.4 (8) 16.8 (5) 25.3 (6) 9.1 (2) 10.3 (4) 21.3 (6)
Birth month and suicide
14
Percent
14
Percent
12
12
10
10
8
8
6
6
4
4
2 0
2 0
43
Natural causes Non Violent suicide JAN FEB MAR APR MAY JUN
JUL AUG SEP OCT NOV DEC
Natural causes Violent suicide
JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC
8.5 8.3 9.3 8.6 8.4 8.4 8.3 9 7.8 8.2 7.5 8.1 13.4 9.3 7.7 8.2 12.9 8.2 6.2 6.7 7.7 6.2 5.2 8.2
Figure 5 Distribution of deaths due to non-violent suicide and to natural causes, by month of birth, in North Cheshire, 1989-2000
Figure 4 Distribution of deaths due to violent suicide and to natural causes, by month of birth, in North Cheshire, 1989-2000
among those who had committed suicide, those born during October to January had, compared to other suicides, significantl y more often employed an overdose rather than hanging as the suicide method. By examining Table 1 for the 502 suicides, we see that in all 194 used an overdose and 136 hanging. Of the 194 overdose cases, 64 were born during October to January; of the 136 hanging cases, 30 were born during October to January. Chi-squar e analysis with a 262 table, with birth season (Oct-Jan, Feb-Sept) vs method (overdose, hanging) , gives w2 4.16 (d.f. 1) with continuity correction (P50.05). So the present study does replicate this result. However, Chotai et al found that among those who had committed suicide, persons born during February to April had significantl y more often employed hanging rather than overdose than did those born in May to January. Similar analysis of 49 overdose cases born during February to April, and 32 hanging cases born during February to April, yielded a chi-squar e value of 0.1 (1 d.f.), which is not significant . So the present study cannot replicate this result. The Swedish findings of season-of-bi rth variations in the serotonin metabolite 5-hydroindo leacetic acid (5HIAA) may be applicable to suicide incidents, mostly of non-violent deaths, in North Cheshire involving those born in winter months. However, in this sample, the incidence of suicides as a whole, regardles s of the method used, appeared to be significantl y higher in those born in May. Violent methods of suicide, particularl y hanging, more frequently go with summer birth dates, quite the reverse of the Swedish results. Perhaps the only conclusion that can be drawn from studies such as this is that seasonalit y of birth in those who commit suicide may reflect the timing of some subtle abnormalities in an early neural migration or differentiatio n process, which might underlie a person’s constitutiona l
vulnerabilit y. A biological basis for suicidal behaviour is possible , as factors that could influenc e brain growth a few months after gestation could affect sensorimotor , cognitive, affective and behavioura l development . This suggestion gives some hope that development al approaches might prove important for understandin g of the psychopathol ogy of depression and suicidal behaviour, and offer new strategies for treatment and prevention.
KEY POINTS . Significant difference s were found among suicides, compared to deaths due to natural causes, with more suicides in those born in May. The distribution of suicide by hanging appeared to be significantl y higher in those born in September and July and lowest in those born in November. . Recent reports suggest that persons born during the winter and spring have significantl y lower values of 5-HIAA, and that low levels of 5-HIAA have been found in persons showing violent suicidal behaviour. . Small sample size and the undetermined study power may limit the inferentia l value of the study. . If suicidal tendencies are affected by biology, there is hope that developmenta l approaches might prove important. . The conflicting findings from different countries in the northern hemisphere indicate the need for future studies.
44
E Salib
Attempts to search for environment al and climatic links with suicide are likely to raise more questions than answers, but seem to follow a consistent pattern, pointing to the constitutional make-up of an individual . The conflicting findings between studies from different countries from the northern hemisphere seem to indicate the need for future multinationa l studies with adequate design, sample size and acceptable statistical power.
ACKNOWLEDGEMENTS The author is grateful to Tracy Flute, Jake Abbas and North Cheshire Health for their help in data collection. My thanks also to Miss Bernie Hayes, Chief Librarian at Hollins Park and Mrs Janet Davies from Pfizer for their support and Miss Katie Spencer for help in data entry and preparation of the manuscript.
REFERENCES 1. Richter J (1990) Does the month of birth affect human biological development processes? Arztl Jugendkd 81: 55 ± 58. 2. Weale R (1993) Is the season of birth a risk factor in glaucoma? Br J Ophthalmol 77: 214 ± 217. 3. Troise C, Voltolini S, Delbono G (1989) Allergy to Parietaria pollen and month of birth. Allergol Immunopathol 17: 201 ± 204. 4. Aberg N (1989) Birth season variation in asthma and allergic rhinitis. Clin Exp Allergy 19: 643 ± 648. 5. Meltzer AA, Spitz MR, Johnson CC, Culbert SJ (1989) Seasonof-birth and acute leukaemia of infancy. Chronobiol Int 6: 285 ± 289. 6. Bell JF, Massey A (1994) The significance of birth dates. Nature 382: 666. 7. James WH (1971) Social class and season of birth. J Biosoc Sci 3: 309 ± 320. 8. Castrogiovanni P, Iapichino S, Pacchierotti C, Pieraccini F (1998) Season of birth in psychiatry: A review. Neuropsychobiology 37: 175 ± 181. 9. Ellsworth H (1938) Season of birth: Its relation to human abilities. New York: Wiley. 10. Pokorny AD (1960) Characteristics of 44 patients who subsequently committed suicide. Arch Gen Psychiatry 3: 314 ± 323. 11. Sanborn DE, Sanborn CJ (1974) Suicide and months of birth. Psychol Rep 34: 950.
12. Lester D (1987) Month of birth of suicides, homicides and natural deaths. Psychol Rep 60: 1310. 13. Kettl PA, Collins T, Sredy M, Bixler EO (1997) Seasonal differences in suicide in birth rate in Alaska natives compared to other populations. Am Indian Alsk Native Mental Health Res 8: 1 ± 10. 14. Chotai J, Salander R, Jacobsson L (1999) Season of birth associated with age and method of suicide. Arch Suicide Res 5: 245 ± 254. 15. Lester D (1995) The concentration of neurotransmitter metabolites in the cerebrospinal fluid of suicidal individuals: A meta-analysis. Pharmacopsychiatry 28: 45 ± 50. 16. Asberg M (1997) Neurotransmitters and suicidal behaviour. The evidence from cerebrospinal fluid studies. Ann NY Acad Sci 836: 158 ± 181. 17. Mann JJ, Malone KM (1997) Cerebrospinal fluid amines and higher-lethality suicide attempts in depressed in-patients. Biol Psychiatry 41: 162 ± 171. 18. Nordstorm P, Samuelsson M, Asberg M et al (1994) CSF 5HIAA predicts suicide risk after attempted suicide. Suicide Life Threat Behav 24: 1 ± 9. 19. Chotai J, Asberg M (1999) Variations in CSF monoamine metabolites according to the season of birth. Neuropsychobiol 249: 57 ± 62.
